(Note: After reading this post, check out A Theory of Laughter—Follow-Up for some additional ideas and elaborations.)

1. tl;dr

There should be parallel explanations for laughter at two levels.

  • At the brain level, there should be some mechanism / algorithm that produces laughter, and it should fit the data of when people laugh in practice.
  • At the evolution level, there should be some explanation for why this mechanism exists in the first place. Why was it adaptive in our ancestors? And where did it come from—are there homologues in other animals?

I’ll summarize my proposals for both of these, in the opposite order:

1.1 First half of the tl;dr: Laughter in terms of evolution

I endorse the popular theory that laughter is an indicator of “play”, homologous to the play-related vocalizations and body language in other animals (e.g. the dog’s “play bow”).

  • The evolutionary purpose of play is “practice for future dangerous situations”. For example, a wolf pup that engages in play-fighting and play-chasing would presumably be more skilled in its future real-life fights and chases.
  • The evolutionary purpose of innate communicative play signals, like laughter in humans and play-bows in dogs, is to reduce the probability of accidental escalation from practice to serious. For example, if a play-fight between two wolf-pups escalates into a real fight between the pups, that’s dangerous for both pups. If the pups are emitting and responding to communicative play signals, then that kind of escalation is much less likely to happen. It’s kinda the same idea as “safewords” in fight-related sports (among other places).

1.2 Second half of the tl;dr: Laughter in terms of brain algorithms

My (oversimplified) pseudocode brain “business logic” for laughter is something like:


  • (A) IF my hypothalamus & brainstem are getting some evidence that I’m in danger
    • (the “evidence” here would presumably be some of the same signals that, by themselves, would tend to cause physiological arousal / increase my heart rate / activate my sympathetic nervous system)
  • (B) AND my hypothalamus & brainstem are simultaneously getting stronger evidence that I’m safe
    • (the “evidence” here would presumably be some of the same signals that, by themselves, would tend to activate my parasympathetic nervous system)
  • (C) AND my hypothalamus & brainstem have evidence that I’m in a social situation
  • (D) THEN I will emit innate play signals (e.g. laughter in humans), and also I will feel more energetic (on the margin), and more safe, less worried, etc.

Indeed, I expect that there is some genetically-specified neuron group in the hypothalamus or brainstem (or more generally, what I call the Steering Subsystem), and that when future scientists look at its various connections and their functional properties, it will be straightforwardly obvious that this neuron group and its connections are implementing the pseudocode above.

(Side note: These scientists will also find that this neuron group has various other inputs that make laughing more or less likely on the margin—inputs related to mood etc.—which I omitted from the box for simplicity.)

Note that nothing in this box is particularly tied to humans. If we’re talking about 50kHz rat laughter instead of human laughter, I wouldn’t change a single word in the box above. However, later in the post, I will talk about human laughter in particular, including humor, and I’ll argue that this pseudocode box is a plausible match to the circumstances in which people laugh.

Also, the path by which I initially came to guess this pseudocode box (namely, introspection) was independent of how I came to believe the evolutionary story (namely, I read it in a book and it seemed obviously right). But I claim that the two stories match up beautifully—that the pseudocode box above is the natural, straightforward way to implement the “spec” associated with the evolution story, given background constraints about how I think brain algorithms work in general (see Section 3.3.2 below). That reassures me that I’m on the right track.

OK, that was the tl;dr. The rest of the article will elaborate on that picture, why I currently believe it, and broader implications.

1.3 Table of contents with section summaries

  • Section 2 will explain the evolution story in more detail.
  • Section 3 will explain the brain algorithms story in more detail—in particular, what exactly do I mean by that pseudocode above? And then I’ll go through three main reasons that I think it's right: (1) the pseudocode matches the evolutionary “spec”; (2) the pseudocode is highly plausible on the neuroscience side; and (3) the pseudocode seems to match the situations in which humans laugh (and in which animals emit analogous play-signals).
  • Section 4 elaborates on the latter by fleshing out how to reconcile the pseudocode with everyday experience, in three domains:
    • Section 4.1 asks: How does this pseudocode shed light on laughter in physical play—tickling, chasing, peek-a-boo, water balloon fights, etc.? For example, why can’t you tickle yourself?
    • Section 4.2 asks: How does this pseudocode shed light on conversational laughter? For example, how is it that laughter can communicate so many different things in different contexts (e.g. friendliness versus aggression, or sincerity versus insincerity)?
    • Section 4.3 asks: How does this pseudocode shed light on humor and jokes?
  • Section 5 asks: How exactly is this pseudocode implemented in the brain? I hypothesize that there are innate connections between neuron groups in the hypothalamus and/or brainstem that directly correspond to the pseudocode above. Alas, I cannot tell you exactly which neuron group it is—I think it’s a neuron group that nobody has studied yet. But I think I know what we should be looking for and where, and I think that a neuroscience lab could figure this out in the near future using standard experimental methods.
  • Section 6 is the conclusion, in which I will discuss how this post relates to my job as an Artificial General Intelligence safety / alignment researcher.

2. The evolutionary story

2.1 What is play, and why do animals have an innate play drive?

central example of play in my mind is two young animals play-fighting or play-chasing each other.

Why are the young animals doing this? There seems to be an obvious primary explanation:

In other words, play is practice for dealing with future dangerous situations.

And what is the evolutionary advantage of having an innate play drive? My answer is: Obviously, squirrel pups do not have the foresight and knowledge to deduce from first principles that it’s a good idea to spend some of one’s free time practicing for future dangerous situations. So instead, play is an innate drive.

In other words: Evolutionarily, play is a means to an end, but from the squirrel’s within-lifetime perspective, play is its own reward—it’s just intrinsically enjoyable.

2.2 What is an innate communicative play signal, and why do animals have them?

Play signals are any vocalizations or body language that happen primarily or exclusively when the animal is playing.

One example is the “play bow” in dogs (which often comes with a high-pitched “play bark”):

Examples of the dog “play bow”

Another is rat laughter, a 50 kHz (ultrasonic) chirp emitted by rats under various circumstances including play-fighting among young rat pups. Jaak Panksepp and his then-student Jeffrey Burgdorf first hypothesized that these chirps are the rat version of laughter in the late 1990s; see for example this 2000 paper by them, which involved manually tickling rats.

(I know what you’re thinking—but don’t worry! Today’s scientists no longer have to suffer the indignity of tickling rats by hand. Instead they can use an “automated protocol for tickling in which … rats are forced to move and interact with a constantly rotating rod”.)

There has been a good deal of follow-up work investigating rat-laughter, some of which I will be referencing below.

So anyway, other animals have play signals. Why should humans be different? And more specifically, our chimp cousins emit laughter-like panting sounds, and “laugh most when tickled, during rough-and-tumble play, and during chasing games (the chimp being chased laughs most)” (that quote and much more in chapter 5 of Provine’s book).

(See: YouTube of a young chimp getting tickled.)

So we arrive at the theory that laughter is a play-signal for humans, homologous to the play signals in other animals. I think this theory goes back to at least Darwin; SEP mentions Max Eastman in 1936. For my part, I originally heard this theory from a chapter in the book Elephant In The Brain by Kevin Simler and Robin Hanson. (I found that book chapter very enlightening, although I don’t agree with everything they said.[1])

Why do animals have innate communicative play signals? Imagine two young squirrels play-fighting. This is a mutually-beneficial activity, for reasons mentioned above. However, it is also possible for two young squirrels to actually fight, an activity which is very dangerous for both of the squirrels, and sometimes also for kin bystanders.

And now we see the problem: there is an obvious resemblance between play-fighting and actual-fighting—such that a play-fight could accidentally escalate to an actual fight. Therefore, each squirrel benefits from communicating to the other that it is play-fighting.

Thus, we expect animals to have evolved innate mechanisms to emit play signals, along with corresponding innate mechanisms to notice those signals and react to them.[2]

3. The brain story

3.1 The pseudocode

I’ll re-copy the box at the top for easy reference—I think it’s something like this:


  • (A) IF my hypothalamus & brainstem are getting some evidence that I’m in danger
    • (the “evidence” here would presumably be some of the same signals that, by themselves, would tend to cause physiological arousal / increase my heart rate / activate my sympathetic nervous system)
  • (B) AND my hypothalamus & brainstem are simultaneously getting stronger evidence that I’m safe
    • (the “evidence” here would presumably be some of the same signals that, by themselves, would tend to activate my parasympathetic nervous system)
  • (C) AND my hypothalamus & brainstem have evidence that I’m in a social situation
  • (D) THEN I will emit innate play signals (e.g. laughter in humans), and also I will feel more energetic (on the margin), and more safe, less worried, etc.

There are presumably various other things that modulate this circuit (a.k.a. shift the thresholds)—person-to-person variation, and variation with age (and certainly with species), and dependence on other innate signals (e.g. angry people tend to laugh less). But I think the box above is the main story.

3.2 What exactly do I mean by “evidence that I’m in danger” etc.? How are these things operationalized?

To be clear, I am not talking about consciously believing that I’m in danger, or safe, etc. For example, my fight-or-flight reaction can easily activate even when I consciously believe I have nothing to worry about, like during a scary movie.

Instead I am talking about innate signals in the hypothalamus and/or brainstem—what I call the “Steering Subsystem”. These signals (I claim) have particular innate “meanings” / algorithmic purposes with legible relation to ecological / homeostatic requirements. For example, see my discussion here of a particular group of neurons in the hypothalamus that is activated by a physiological need for food, and causes various downstream effects (like energy conservation and hunger sensations) that are appropriate to that state. These kinds of innate signals can exist even if we have no conscious (interoceptive) access to them, and no common English-language concept that perfectly aligns with them. (See my recent post on where I disagree with Lisa Feldman Barrett.)

Anyway, I suggested in the box above that “danger” might be operationalized via some of the same innate signals that activate the sympathetic nervous system (directly or indirectly), and “safe” might be operationalized via some of the same innate signals that activate the parasympathetic nervous system (directly or indirectly). Which signals exactly? I don’t know.

What about ingredient (C), the “social” innate signals? I’m not sure about that either. But there do seem to be innate signals in the hypothalamus and brainstem that are intended (by evolution) to correlate with being in a social situation. One obvious way for evolution to calculate such signals is via heuristics calculated in brainstem sensory processing systems. For example, a recent preprint I like—Liu et al. (2023)—identified two groups of cells in the hypothalamus (medial preoptic nucleus). The activity of one group correlated with being socially isolated, and the activity of the other group correlated with the end of that isolation. Interestingly, they found that, as far as these two cell groups were concerned, “social” was being operationalized via touch sensations—not sound, not pheromones, it had to be touch. (The mice were blind so they’re not sure about vision.) But that finding of the centrality of touch does not generalize to other social instincts. For example, another rodent social instinct is mating, and here, the innate circuits are triggered at least in part by pheromones. Anyway, in sum, I don’t know exactly how “social” is calculated for the purpose of Ingredient (C) of laughter in rodents, let alone in humans, but such a calculation is definitely a thing that the brain can do.

3.3 Three reasons I like this proposal

3.3.1 This pseudocode matches the evolutionary “spec” of Section 2

I think the correspondence here is strong and straightforward, and I see this as key evidence that I’m on the right track. Going through the items above:

  • (A)—some evidence that I’m in danger. If I’m in a situation that is triggering some fight-or-flight bodily reactions—regardless of the exact reason—then I’m almost definitely in a situation that resembles dangerous situations that I might get into in the future. And therefore, being in this situation almost definitely constitutes good “practice”.
  • (B)—stronger evidence that I’m safe. Without this ingredient, it’s not “practice”—it’s the real thing! I should be getting out of the situation, not rushing into it! I should find it aversive, not fun.
  • (C)—evidence that I’m in a social situation. Without this ingredient, it still qualifies as “practice”, and thus it is still evolutionarily adaptive to stay in this situation, and therefore our evolutionary expectation should be that a situation would be “fun” even without ingredient (C). But without ingredient (C), I don’t expect to laugh, evolutionarily speaking. There is no point in emitting a communicative signal, if there is no one around to hear it.

I put in ingredient (C) based on various studies (in both humans and rats) that much more laughter occurs when conspecifics are around. For example, Provine found that laughter was 30× less frequent when people were alone.[3] (I think watching TV by oneself is an intermediate case—the TV presumably tricks our brains into thinking we’re in a social situation, at least to some extent.)

So for example, my theory would be: If I go on a roller coaster with friends, we may well be laughing together during the scary parts; whereas if I go for a ride on an otherwise-empty roller coaster, with nobody in eyeshot or earshot, then I’m much less likely to laugh out loud, but I’ll still probably find it fun. Likewise, if I’m alone, I might want to read a humorous book, even if doing so will probably not make me laugh out loud.

3.3.2 This kind of pseudocode is highly plausible on the neuroscience side

Unfortunately, despite some effort, I cannot tell you the exact neurons that implement the pseudocode in the box above. See Section 5 below for more details.

However, the pseudocode above is fully compatible with everything I think I know about the brain. And that counts as strong evidence for me, because "the things I think I know about the brain" are highly constraining! (For some of those constraints, see my post “‘Learning from Scratch’ in the Brain”. And see my post on social instincts for an example of how those constraints rule out lots of possibilities in practice.)

In particular, I know that the right kind of signals are in fact present in the hypothalamus & brainstem (see Section 3.2 above), and I know that the genome is easily capable of building a little cluster of neurons in (probably) the hypothalamus that perform the requisite logical operations. I have seen lots of little clusters of neurons in the hypothalamus doing broadly this kind of genetically-specified business logic.

3.3.3 This pseudocode seems to fit the data of when humans laugh (and when animals emit analogous play-signals)

As far as I can tell, the pseudocode is compatible with all our experience of laughter in humans and corresponding play-signals in other animals, including all three of the categories elaborated in Section 4 below—physical play in Section 4.1, non-“humor” conversational laughing in Section 4.2, and humor in Section 4.3.

You can read Section 4 to better understand where I’m coming from. But then you should take a long hard look at the pseudocode box in Section 3.1 above, and then scroll down to the comments section, and complain about some situation where the predictions of that pseudocode box are wrong!

…And then I’ll respond with things like:

  • “OK sure, but that’s because the pseudocode box of Section 3.1 is oversimplified, like I left out how the laughter-reaction is suppressed by other innate signals correlated with anger and mating and some other things like that.”
  • “OK sure, but I was using words like ‘safe’ and ‘dangerous’ when obviously those are just the closest English-language words I can think of, not perfect descriptions, and they come apart from the actual innate signals in various ways, which by the way I cannot specify in detail”.

…And then you will roll your eyes at me and accuse me of special pleading and unfalsifiability.

Totally fair!

But I still currently think I’m getting much more out of this pseudocode box than I’m putting in—and that’s even without knowing exactly where the corresponding neurons are and what they’re connected to.

(But please do leave those kinds of skeptical comments! They will be very appreciated!)

4. Relating the pseudocode to everyday experience

There isn’t a sharp line between them, but I’ll separately discuss three categories: laughter in physical play, laughter in non-“humor” conversation, and humor. In that order:

4.1 Laughter in physical play (e.g. tickling, chasing, peek-a-boo, etc.)

(This is the most straightforward case, and also the case where humans are most similar to other animals.)

Examples of kids laughing during physical play—getting tossed in the air (left) or sprayed with a water gun (right). Image sources: 1,2

4.1.1 What are the sources of “Ingredient (A)” (i.e., evidence of danger / cause for physiological arousal) in physical-play laughter?

In physical-play laughter, I think there are many possible sources of Ingredient (A), and they’re mostly pretty obvious. In particular, we (like almost all animals) have a diverse suite of innate defensive reactions, including in our case:

All of these innate reactions trigger not only certain muscle behaviors, but also physiological arousal—hence Ingredient (A).

And all of these are situations where you’ll see little kids laughing uproariously during physical play.

4.1.2 More discussion of tickling in particular

It strikes me as extremely obvious that tickling is part of play-fighting. For example, the most ticklish parts of your body seem to coincide with the parts that are most vulnerable to serious injury, like the front of the neck.[4] So the evolutionary story behind tickling is straightforward. What about the brain-level story?

I claim that the pseudocode of Section 3.1 above is perfectly adequate to explain everything about tickling at the brain-level. To flesh that out, here are some additional details and discussion:

The source of Ingredient (A) in tickling is basically the normal startle and orienting responses to unexpected sensory inputs, as mentioned above. But, for obvious evolutionary reasons, those innate reactions are presumably especially strong for touch sensations on vulnerable parts of your body. Think of the circumstances when those reactions would naturally trigger—maybe there’s a scorpion crawling on your neck, or maybe your enemy has successfully gotten his hands around your neck during a fight, etc.

You can’t tickle yourself for the same reason that you do not routinely have an involuntary startle reaction from the sound of your own voice when you start talking, and the same reason that you do not routinely have an involuntary orienting reaction when you wave your own hand in front of your own eyes. (Unless of course you have schizophrenia—see here—or if you are an infant surprising yourself by making a funny noise for the first time, etc.)

The source of Ingredient (B) in tickling is the knowledge that you’re safe among trusted friends. If you’re getting “tickled” in a situation where you’re genuinely terrified for your own safety, my impression is that you’re going to be screaming rather than laughing.

Related to this, even if someone enjoys getting tickled in general, they will still try to push your hand away from the most ticklish areas. The evolution-level reason for this behavior is obvious: that’s part of how play-fighting works. It would hardly be good defense practice otherwise! But what about the brain-level reason? I propose that when their sensitive areas are successfully getting tickled, Ingredient (A) gets so strong that it cuts off Ingredient (B), tipping the experience from fun into aversion.

4.2 Laughter in non-“humor” conversation

4.2.1 Background: Most conversational laughter is not “humor”

Even if we ignore physical play, the connection between “humor”[5] and laughter is less tight than you might think. In Provine’s book he talks about his “ecological” studies of modern USA people hanging out in public, and says “only about 10%-20% of [comments immediately preceding somebody laughing] were estimated by my assistants to be even remotely humorous”. Then follows a helpful table of typical laugh-eliciting comments, including such zingers as “I’ll see you guys later!” and “Can I join you?”

Pay close attention next time you’re in (or overhearing) a normal face-to-face group conversation, and you’ll probably notice something similar.

Other cultures seem to be similar to the USA in that respect—for example this article talks about hunter-gatherers laughing in response to gentle teasing and such—not “why did the chicken cross the road”.

4.2.2 What are the sources of “Ingredient (A)” (i.e., evidence of danger / cause for physiological arousal) in conversational laughter?

Section 4.1.1 listed a bunch of obvious ways that arousal gets invoked in physical play, like if you think you’re alone but someone suddenly jumps out at you from hiding while screaming at you. But what about conversation—can mere words invoke physiological arousal too? Yes, obviously! Wandering into a stressful conversation topic can get your heart rate up just as surely as can wandering into a swarm of angry bees.

To be more specific, it seems to me that there are a great many natural sources of Ingredient (A) in conversations, including:

  • Confusion
  • Embarrassment / guilt / shame (possibly vicarious)
  • Disgust (possibly vicarious)
  • Surprise (possibly vicarious)
  • Threats (both bodily threats and status threats) (possibly vicarious)
  • Taboo-breaking

These are not mutually-exclusive, and there are others too.

4.2.3 Laughter communicates a pretty universal message about my transient “internal” state, but then the listener has to infer why I feel that way, and the latter inference is complicated, contextual, and widely-varying.

Remember from Section 2 above, I’m claiming that “avoiding accidental escalation during practice for future dangerous situations” is the evolutionary explanation of why the brain mechanism for laughter is there in the first place. But given the existence of that brain mechanism, it will be active in lots of situations, many of which may have nothing to do with “avoiding accidental escalation during practice for future dangerous situations”. (See “Adaptation-executors, not Fitness-maximizers”.) And I think this is much more true in humans than in other species, who seem to mostly just laugh during play-fighting, play-chasing, etc.

In all situations, I think the universally-shared “meaning” of laughter is related to certain signals in the head of whoever is laughing, as specified by the pseudocode of Section 3.1. But then the listener needs to infer from context why those signals are in the laugher’s head. And here things get very complicated and contingent. Some examples:

  • Scenario 1: You are walking by me in middle school, when I just dropped my contact lens. I say “please help me” with a desperate tone, and you laugh as you say “sorry, I don’t help losers”.
  • How I might take that: I know that you feel safe (ingredient (B)), and I might guess that it’s because I’m in your outgroup and that you regard my suffering as no threat to your own well-being. I also know that you feel a bit of ingredient (A), and maybe I’ll guess that you feel like it’s cringe that I even dared ask you for help in the first place. In short, your laughter communicated to me that you feel unsympathetic and superior.
  • Scenario 2: You are my spouse. I say “Man, my company is really dysfunctional”, while slightly laughing, and in response you laugh as you say “yeah”.
  • How I might take that: Well, for my part, I was laughing mainly because I felt kinda annoyed about the dysfunction (Ingredient (A)), but also not overly worried for my own sake (Ingredient (B)). Then when you laugh in your response, I might infer that you are invested in my well-being, and empathetically mirroring my feelings on both counts. In short, your laughter communicated to me that you feel empathy and camaraderie.

I could go on. I think that, in different contexts, laughter can signal friendship, or animosity, or superiority, or inferiority, or sincerity, or insincerity, etc. etc. There is no simple theory, because we can feel a certain way for many unrelated reasons. 

4.2.4 …And given that laughter is able to communicate stuff, people skillfully wield laughter as part of their communicative toolkit

In the previous section I was implicitly treating laughter as an incidental side-effect of the emotions that someone feels in the course of a conversation. But once humans have learned (consciously or unconsciously) that laughter communicates things, they will start wielding laughter to skillfully advance their communicative intentions. For example, in Scenario 2 just above, maybe you laughed in part because you wanted to communicate empathy and camaraderie.

This doesn’t have to be a conscious explicit decision or desire, and in fact it probably usually isn’t. It’s probably more often an unconscious habit—in lots of previous conversations, you’ve laughed or not-laughed in a certain way in a certain context, and it led to good results, so you unconsciously learned to repeat that behavior next time you’re in a similar situation.

While purposeful control of laughter is not directly part of the “business logic” I wrote down in Section 3.1, we obviously can in fact voluntarily laugh. Mechanistically, I think it typically (though not always[6]) happens indirectly—if we want to laugh, we steer ourselves into a transient emotional state that has Ingredients (A-C), and if we want to not laugh, we steer ourselves into a transient emotional state that doesn’t have all three ingredients. How do we do that? Well, we have some control over our transient emotional state because we can attend to some aspects of our situation rather than others, choose which frames / analogies to mentally invoke, etc.

4.3 Humor

As mentioned in 4.2.1 above, humor does not necessarily cause people to laugh, and most laughter occurs in the absence of humor.

That said, humor can obviously lead to laughter, so I ought to briefly say something about how. I don’t have a grand theory of humor, nor do I think there is one, beyond what I’ve already said in this post. I’ll just mention a few considerations that I find helpful to keep in mind when thinking about humor and jokes.

4.3.1 What are the sources of “Ingredient (A)” (i.e., evidence of danger / cause for physiological arousal) in humor?

I think the list is pretty similar to Section 4.2.2 above for conversational laughter above. I won’t re-copy it—you can scroll up. Again, that list is not exhaustive, nor mutually exclusive.

4.3.2 There’s an inverted-U dynamic for “Ingredient (A)”

According to the pseudocode box above, if there is too little of Ingredient (A), there’s no laughter (e.g. a boring conversation), and if there’s too much (A), then there’s also no laughter, because it undermines Ingredient (B) (e.g. it might just feel stressful, painful, scary, confusing, etc.) Somewhere in between is optimal for laughter.

So I think we wind up with inverted-U dynamics like this:

My theory predicts an inverted-U dependence between Ingredient (A) (in the pseudocode box above) versus laughing—more (A) leads to more laughing, until it’s so much that it cuts off Ingredient (B) and tips to aversion. (See prior discussion of lots of proposed inverted-U’s in humor in Martin & Ford 2018.)

(I was implicitly talking about this same inverted-U in Section 4.1.2 above, when discussing why someone might enjoy getting tickled a little bit, but find direct tickling of their most ticklish spots to be too much, and thus aggressively push the tickler away.)

4.3.3 The (somewhat arbitrary and drifting) cultural expectations / tropes / rituals surrounding “humor” can be a key component of the explanation of why something is funny.

In particular, if a listener has a general cultural expectation that “humor” should involve X (e.g. a punchline), then a joke-teller can either:

  • Increase the amount of Ingredient (B) by conspicuously including X (e.g. an obvious punchline), OR
  • Increase the amount of Ingredient (A) by conspicuously excluding X (e.g. punchline-free absurdist anti-humor)

Either of these can be helpful for the joke, depending on how much (A) and (B) are present from other sources.

And if the latter (exclusion of X) happens a lot, then we collectively stop expecting X in the first place, causing gradual (anti-inductive[7]) drifts in what people find funny, or schisms between humor-subcultures.

4.3.4 I’m not generally impressed by “theories of humor” beyond their overlap with the discussion above.

For example, the Psychology of Humor textbook (Martin & Ford 2018) describes three “classic theories of humor” which I will comment on in turn:

  • “Relief theory” seems to capture the kernel-of-truth that many instances of humor follow the following time-course: first, we have a bunch of Ingredient (A), and second, something changes and introduces a heap of Ingredient (B) (while the (A) has not yet fully faded from our brainstems). Those two steps can be described as “tension” and “relief of tension” respectively.
  • “Superiority theory” seems to capture the kernel-of-truth that, in many instances of humor, Ingredient (A) is vicarious—from imagining someone in danger or duress—while Ingredient (B) comes from my comfort in the knowledge that I, the listener, am not that person, and am superior to that person, and have therefore nothing to fear for myself.
  • “Incongruity theory” strikes me as a mishmosh of different things. For example, Ingredient (A) can be based on the feeling of confusion, and (B) by its resolution. Or Ingredients (A) and (B) can come from different (incongruous) ways to view the same situation, one of which is normal / safe and the other embarrassing / dangerous / etc. In still other cases, I wonder whether we’re all just following a cultural telling-a-joke script, and as a listener, Ingredient (A) is my concern that I don’t “get the joke” and will be embarrassed to admit it, and Ingredient (B) is my relief when I do.[8] It can also be several of these things simultaneously, and more.

After that, the textbook moves on to discuss three “contemporary theories of humor” (“reversal theory”, “comprehension-elaboration theory”, and “benign violation theory”). My comments on those would largely overlap with the above bullet points, so I’ll just move on.

5. More detailed discussion of the neuroscience

5.1 Overview

The kind of “business logic” pseudocode of Section 3.1 is to be found, I claim, in what I call the “Steering Subsystem” (hypothalamus and brainstem—see definition and discussion here). My guess is more specifically as follows:

Speculative diagram of some of the key hypothalamus & brainstem (“Steering Subsystem”) pathways involved in laughter. This diagram is mostly based on an old review of squirrel monkey data (Jürgens 1998), combined with my general preconceptions about how these things ought to work (e.g. see Fig. 9 of Swanson 2000), plus Gloveli et al. (2023) which recently nailed down the “motor pattern initiator(s)” box in the upper-left. See text for more details and caveats.

5.2 Where exactly in the brain is the “laugh behavior controller” (top box in that diagram) where I can read out the alleged pseudocode of Section 3.1?

Sadly, I have failed to deduce from existing literature where in (probably) the hypothalamus we would find the core “business logic” pseudocode of Section 3.1. (It could also be split among a couple places.)

Focusing on rats (although I expect the answer to be similar in humans), one candidate mentioned in the literature is the so-called “parvafox nucleus” of the lateral hypothalamus. Check out Alvarez-Bolado & Celio (2016) for an argument along those lines. As far as I can tell, the strongest evidence in favor of this hypothesis is that bilateral destruction of the parvafox nucleus dramatically (factor of >10) reduces rodent laughter, according to Roccaro-Waldmeyer et al. (2016). Relatedly, there is some evidence (including from laughter-inducing “gelastic seizures”) that “stimulations of [the] tuberal portion [of the lateral hypothalamus] provoke bursts of laughter” (Alvarez-Bolado & Celio (2016)), and that’s in the general vicinity of parvafox.

However, I think the current balance of evidence is that parvafox is not the controller for laughter, but rather is related to defense behavior—based on both direct stimulation of those cells (e.g. Cola et al. (2023)), and looking at where in the brain they project to (e.g. Celio et al. (2013)Bilella et al. (2016)). We still need to explain the Roccaro-Waldmeyer results from the previous paragraph, but there are a couple possibilities for that, including (1) that parvafox is essential for “Ingredient (A)” of the pseudocode of Section 3.1 (and thus upstream of laughter), or (2) that parvafox is physically proximate to the “real” laugh behavior controller and that Roccaro-Waldmeyer destroyed the latter accidentally in their experiments. (Lesion experiments are notorious for “collateral damage” of nearby neurons and fibers, if I understand correctly, but be warned that I’m not an expert.)

Well, if it’s not parvafox, then what is it?

I don’t know. If someone wanted to make progress on this question experimentally—to actually find that pseudocode implemented via innate brain signaling pathways—I think an obvious immediate next step would be a retrograde neural tracing experiment starting from the (lateral) part of periaqueductal gray (PAG) associated with laughter (as pinpointed in the very recent article Gloveli et al. (2023)), followed by further characterization of whatever upstream neuron-groups show up. Maybe such data already exists, and I missed it. (Parvafox does not seem to project to the correct part of PAG to match up with the Gloveli et al. neurons, as far as I can tell, although I’m not super-confident.)

Areas that I see as especially suspicious include:

  1. neurons nearby but not part of the parvafox nucleus, in the tuberal region of lateral hypothalamus (for reasons stated above);
  2. neurons somewhere in or around the medial preoptic area of the hypothalamus—for which stimulation can cause rat laughter (Wintick & Brudzynski (2001)), and which is known to be the home of the main behavior controllers for at least two other positive social behaviors that I know of, namely the behavior studied by Liu et al. (2023) mentioned above, plus aspects of mating as discussed in Bayless et al. (2023);
  3. more generally, the rest of the hypothalamus too.

5.3 What about the “Learning Subsystem” (cortex, striatum, amygdala, hippocampus, etc.)?

As I described here, I claim that the brain should be divided into two subsystems, the “Learning Subsystem” which runs randomly-initialized learning algorithms, and the “Steering Subsystem” which runs “business logic”. Above I was only talking about the “Steering Subsystem”; but in fact laughter also interacts with the “Learning Subsystem”—i.e., the cortex, striatum, amygdala, hippocampus, thalamus, cerebellum, etc.

I claim that  the laughter-triggering signals coming from the Learning Subsystem are in the following two categories:

  • (A) Outputs trained by reinforcement learning to maximize some signal from the Steering Subsystem (hypothalamus & brainstem) that acts as a “reward”, or
  • (B) “Short-term predictors” of some signal from the Steering Subsystem.

For example:

  • An example of (A) would be voluntary / learned control of laughter (Section 4.2.4).
  • An example of (B) would be a “self-fulfilling prophecy”, where you laugh because you’re in a situation that pattern-matches to other situations that have caused you to laugh in the past.

I think there are probably other examples too, but that’s outside the scope of this post.

Direct evidence that the cortex is not necessary for play is provided by “decorticate” rats (= rats whose cortex has been surgically removed), whose play is “much the same [as] controls” (Whishaw 1990Panksepp et al. 1994). I can’t immediately find direct measurements of the presence of the normal 50kHz “laughing” vocalizations in decorticate rats while they play, but if their play is similar in other respects, I would certainly guess that they are also vocalizing in a roughly normal way.

6. Conclusion

I remain adamant that the hypothalamus and brainstem are full of hundreds-to-low-thousands of specific neuron groups with specific connections that are all written directly into the genome, and which correspond to “business logic” that makes evolutionary sense—things like “if you’re malnourished, reduce your sex drive”. I think that understanding this tangle of “business logic” is annoying but possible, and that doing so seems possibly helpful for Artificial General Intelligence (AGI) safety and alignment, for reasons spelled out here.

I consider laughter an “easy” example of such business logic, as compared to something like the human innate status drive (assuming that there is a human innate status drive, which I currently believe but am not 100% sure). I think the human innate status drive would need substantially more convoluted pseudocode than the box in Section 3.1, and I don’t even have a plausible guess right now for how it works in detail. (See here for vague thoughts.) So maybe this post on laughter is a warm-up. In particular, I don’t think this post is directly important for AGI safety—if we iron out the details of the pseudocode of Section 3.1, and put it into the source code of future AGIs, and then we find that those AGIs are laughing in a vaguely-psychopathic-human-like way while they mercilessly murder me and my family and every other human … then that doesn’t really make me feel much better!

Still, even if understanding laughter is just a “warm-up” for more safety- and alignment-relevant things like compassion and friendship, I am still very interested in getting this right! I spent much longer on this blog post than usual (admittedly a low bar), including trying to be reasonably comprehensive in reading relevant sources, etc., and I am very eager for feedback. 

(Thanks Seth Herd, Linda Linsefors, Justis Mills, and Miguel De Guzman for critical comments on drafts.)

  1. ^

    Since the works of Robin Hanson are popular on this forum, I will say a bit more about where I differ from Elephant In The Brain. My biggest complaint is the part where they say:

    As we mentioned earlier, people are profoundly ignorant about laughter’s meaning and purpose (at least in our default state, before learning the science). But where does this ignorance come from? Why does introspection fail us so spectacularly here?

    It’s not simply because laughter is involuntary, outside our conscious control. Flinching, for example, is also involuntary, and yet we understand perfectly well why we do it: to protect ourselves from getting hit. Thus our ignorance about laughter needs further explanation.

    I disagree that it “needs further explanation”. I think we start out ignorant of literally everything, until we learn it / figure it out. And I think that figuring out the evolutionary purpose of laughter is just inherently much harder than figuring out the evolutionary purpose of flinching. It’s less obvious / salient, for various reasons that I claim are pretty obvious if you think about it. I don’t think there’s any more to it than that.

    I also don’t think there can be more to it than that. To explain what I mean by that, imagine if I said: “Here’s the source code for training an image-classifier ConvNet from random initialization using uncontrolled external training data. Can you please edit this source code so that the trained model winds up confused about the shape of Toyota Camry tires specifically?” The answer is: “Nope. Sorry. There is no possible edit I can make to this PyTorch source code such that that will happen.” By the same token, even if, as that book argues, there is a strong evolutionary pressure to make humans specifically confused about the evolutionary purpose of laughter, I don’t think there is any possible genetic change that would make that happen. Related discussion here.

  2. ^

    Whenever there’s a claim about communicative signals, one can ask a follow-up question of whether these signals are game-theoretically stable against “lies”. Like, what if Squirrel A laugh-squeaks to signal play, then Squirrel B lets down its guard, then Squirrel A attacks for real? If this happened a lot, wouldn’t squirrels eventually evolve to ignore play signals? And if that happened, then wouldn’t squirrels further evolve to stop emitting play signals in the first place? Good question! It’s worth thinking about those kinds of things. But I do think a good answer exists, even if I don’t know it in full detail. I think there are various ways that signals can be hard or costly to fake. And I also think that animals treat a play-signal by itself as insufficient reason to let down one’s guard, which reduces the benefit of lying. Animals are reacting to other cues too, like whether there is an existing trusting relationship. For example, if I’m a prisoner, and the cruel guard is pointing at me and laughing, that sure wouldn’t make me feel more relaxed.

  3. ^

    I think Provine’s claim that there’s 30× more laughter in social situations is less clear-cut than it sounds. In fact, it’s hard to do an apples-to-apples comparison of laughter in social versus nonsocial situations, because (1) social situations are drawn from a different distribution from nonsocial situations in many respects, (2) the presence of other people can change Ingredients (A) and (B) too, and (3) social situations can also affect laughter via voluntary control (Section 4.2.4). I still think (C) is probably a real ingredient in the algorithm, because Provine’s factor of 30 is so extreme that it seems difficult to fully explain by any of those indirect mechanisms.

  4. ^

     I’m extremely far from an expert on what parts of the body are vulnerable in combat today, let alone 100,000 years ago (How often were people punching each other, versus slashing with sharp rocks, versus getting bitten by wolves or spiders? What were the lived consequences of different types of injuries? Beats me!). But I still think this claim is probably true. For example, this article claims that ticklish areas correlate with areas protected by involuntary defensive reflexes.

  5. ^

    I am defining the word “humor” narrowly—something like “humor = the kind of stuff you find in the ‘humor’ section of a bookstore”, e.g. recognizable jokes and so on. On this definition, if someone walks up to my lunch table and says “can I join you?” and then laughs a bit, that’s conversational laughter but not “humor”. I believe Provine takes this definitional approach.

    Alternatively, one could define the word “humor” very broadly, as something like “humor = whatever makes someone spontaneously laugh”. On this definition, it’s perfectly possible that someone walking up to my lunch table and saying “can I join you?” is an instance of “humor”, when taken with its full context. I believe Hurley et al. take this definitional approach.

    Anyway, this is just semantics. “Humor” is just a word, and within limits, we can define it however we want. I find the narrow definition to be helpful for the purposes of this post, so that’s how I’m using it.

  6. ^

    Transient manipulation of our own emotional state is not the only method of learned / deliberate manipulation of laughter. Alternatively, you can laugh by pure voluntary motor control—just move your larynx, lungs, etc. and make laugh sounds, the same way you might voluntarily move your arm. I think such laughter can come across as fake sometimes (like maybe it can sound slightly different, and the eyes don’t squint in quite the same way, see Duchenne smile)—although people still do it plenty.

    Incidentally, I think the “summoning transient emotions” method of laughing and the “pure voluntary motor control” method of laughing in this footnote are probably two opposite ends of a spectrum, as opposed to a crisp binary.

  7. ^

    If you haven’t heard the term “anti-inductive”: "Inductive" reasoning is where you assume that if you’ve seen something a bunch of times in the past, then it’s likely to happen again in the future. “Anti-inductive” reasoning is the opposite—the more past evidence you have for something, the more likely it is to be false next time.

    As the old joke goes: “I recommend anti-inductive reasoning to anyone. After all, using anti-inductive reasoning has been a catastrophically bad idea every time I’ve tried it in the past. So it’s definitely a good idea going forward.”

    Here’s an example. If you’re up against a master at rocks-paper-scissors, you might want to use anti-inductive reasoning about the future: The more evidence you have for a pattern in your opponent’s behavior, the likelier it is that your opponent wants you to notice that pattern, and therefore the more you should expect that pattern to reverse on the next throw. (But this is happening at every level of abstraction simultaneously—which is kinda weird to think about.)

  8. ^

    I suspect that kids will laugh a comparable amount in practice when solving a riddle / brainteaser posed by a friend as when “getting” a pun told by the same friend, other things equal. Other things are not always equal though; puns often get an extra emotional “kick” from some other source, like from being sexual, or from the friend’s mood, or just from the very fact that it’s a pun, both because there’s a cultural trope that making puns is a shameful activity, and because puns are “supposed” to be funny and the expectation of laughter can be a self-fulfilling prophecy, see Section 5.3 below.

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13 comments, sorted by Click to highlight new comments since: Today at 10:31 AM

I think I'm much more of an incongruity theorist than this (though haven't read the literature). More specifically: Humor generally involves playing around with frames / scripts, often crashing different frames together in interesting ways. Laughter involves distancing yourself from a frame you're engaging with, so that you're kinda acting with that frame but not fully immersed in it.

This fits the playfighting evolutionary context, which is engaging largely within the "fight" frame while keeping some detachment from it.

There is also a thing about social syncing on a shared frame, when the frame isn't the obvious default (we both understand that this is not a real fight, just a play fight, hahaha). Which seems related to how "getting the joke" is such a central aspect of humor. And to how humor is involved in social bonding.

My experience of coming up with in-context jokes matches this theory much more than your theory. It generally starts by noticing some alternative interpretation or frame on something that just happened (e.g. something that someone said), then gets refined into a specific thing to say by some combination of trying to find the most interesting interplay / biggest tension between the two frames, and trying to best bring in the new frame, and fitting it all to the people around me and what they'll understand & like. I'm not trying to track the amount of danger or the amount of safety. (Though maybe sometimes I'm tracking something like the level of physiological arousal - at some point you swapped that in for "danger" and it does resonate more.)

For a concrete example to talk about, I looked through recent SMBC comics and picked out the one I found funniest - this one. It is a good example of crashing two frames together, the Disneyfied frame on wild animals interacting with humans and a more realistic one, brought together by a picture that can be seen from either viewpoint. The phrase "tickborne diseases" really makes the realistic frame pop. Though there's also definitely some danger vs safety stuff happening here, so it's not a counterexample to your theory.

This other recent SMBC is also funny to me, and also has the playing around with frames thing without any obvious danger. So maybe is a counterexample? Though not sure if trying to find counterexamples is an important exercise; your theory seems more like it's incomplete than like it's totally wrong.

Trying my own hand at theorizing about this danger/arousal/whatever thing... Seems like there's something about the content (at least one of the frames) being important to the person. So danger, sex, taboo things. Pulling on some sort of relevance / importance / salience system in the brain.


This other recent SMBC is also funny to me, and also has the playing around with frames thing without any obvious danger. So maybe is a counterexample? Though not sure if trying to find counterexamples is an important exercise; your theory seems more like it's incomplete than like it's totally wrong.

I’m asking myself: Where's the physiological arousal (increased heart rate etc.) in the SMBC you linked? My tentative answers are: Maybe a bit of surprise, but also I think there's some interpersonal tension from the fact that the people on the right are belittling the people on the left, including vicarious embarrassment when we imagine that the people on the left have revealed themselves (well, ourselves) to be morons, plus a side-dish of invoking sex and violence. I think if we removed all those things, there would be no humor left.

Like, suppose I say to you: “Once upon a time, Goldilocks was wandering through the woods, and came upon a little house. Oh by the way, it's gonna take me about 4 minutes to tell you this story.” I just changed frames—from the fictional within-story frame, up a level to the nonfiction real-world frame in which we’re sitting here and I'm telling you a story. But that transition wasn’t funny at all, right?

Or here's another example of playing with frames where there's no physiological arousal and hence no laughter: “You know that bag of candy in your hands? It's rectangular.” I invoked a different frame than what you were previously thinking about, but there's no Ingredient (A), and hence no laughter.

Humor generally involves playing around with frames / scripts, often crashing different frames together in interesting ways.

Hmm, here’s an idea. Maybe the very same thought can’t trigger both Ingredient (A) and Ingredient (B), because there’s mutual inhibition or something. So that suggests that we can only get laughter in two ways:

  • Ingredient (A) doesn’t come from “a thought” at all, but rather straight from the brainstem, e.g. getting tickled.
  • We think two consecutive thoughts, of which one creates Ingredient (A), and the other creates Ingredient (B), and maybe we flip back and forth between those two thoughts a few times within a second or two, such that both ingredients wind up present in the hypothalamus / brainstem simultaneously. And thus we get laughter.

Then the second bullet point would suggest that it’s difficult or impossible to get humor or conversational laughter except by situations that can be viewed / analogized / framed in at least two different ways.

Do I believe that previous sentence? Hmm, I dunno.

  • I think I’m fully on-board with “that’s one way to invoke laughter”,
  • I’m uncertain about the much stronger statement “that’s pretty much the only way to invoke conversational laughter”,
  • I’m definitely against the even stronger statement “switching back and forth between two different frames is not only necessary but also sufficient for laughter”.

(I definitely don’t think it’s sufficient—the other condition would be that one of the frames creates Ingredient (A) and the other creates Ingredient (B), cf. those non-funny examples above.)

I need to ponder it more. But that was a very fruitful comment, thank you :)

Actively searching for counterexamples to the post's danger+safety theory... What about when people who are in love with each other get giggly around each other? (As an example of laughter, not humor.) I mean the sickly-sweet they're-in-their-own-world-together kind of giggling, not the nervous unsure-of-oneself laughter. Doesn't seem like there's danger.

Similarly, people laughing more when they're on drugs such as weed. (Though that seems more open to alternative physiological explanations.)

Do the stoners and giggly lovers fit the sketch of a theory that I'm maybe building towards? There is playing around with frames in both of them, I think. People on drugs see things fresh, or from a different perspective from usual; lovers-in-their-own-world have stepped out of the default social framework for interacting with the social world into their own little world. There is definitely syncing on frames with the lovers, though often not with the people on drugs. And there's an importance thing going on in the relationship, and a perception-of-importance thing with drug use. So mostly fits, except with an exception on the syncing bit.

Giggly lovers is a good example of why I maybe should have just used the term “physiological arousal” throughout, instead of the word “danger”. I think it's just generally exciting / stimulating / etc. to be newly in love! There's a lot of Ingredient (A) floating around, even if there isn't really any “danger” in the normal sense of that word. (It’s high-stakes in regards to one’s reproductive prospects, I guess.)

Not sure about marijuana. Maybe I’d guess that the chemical somehow sets Ingredients (B) + (C) anomalously high, so that almost any physiological arousal triggers laughter, even things that would normally just be scary or exciting. Like laughing through an entire episode of Oz (true story, if I recall correctly from a very long time ago).

This is much closer to my model of humor as well. I think most humor can be categorized as novel patterns of ideas at a certain level of abstraction, that the brain is not used to processing.When the brain gets used to the pattern, the joke and similar jokes are no longer funny.  

I find it unlikely that sexual selection hasn't played a major role in the development of humor given that people report it as highly attractive. If humor is mostly novel patterns, then pattern recognition is a skill required to be good at it. Being funny could therefore be a proxy for intelligence. This seems to be he case if you look at the IQ scores of comedians. 

Displaying honest signs of intelligence seems adaptive in general in a social primate for various obvious reasons. Combining novel frames might also allow you to convey a concept in a way that is challenging a taboo without risking to actually make statements that are taboo. A useful tool in ancestral politics. 

The playfighting theory does a very good job of explaining why tickling and scaring people make people laugh on the other hand. My guess is that humor and laughter started out with the evolutionary purpose described by the theory, before being adapted for other purposes like sexual selection and tribal politics.   

What about puns? It seems like at least some humor is about generic "surprise" rather than danger, even social danger. Another example is absurdist humor.

Would this theory pin this too on the danger-finding circuits -- perhaps in the evolutionary environment, surprise was in fact correlated with danger?

It does seem like some types of surprise have the potential to be funny and others don't -- I don't often laugh while looking through lists of random numbers.

I think the A/B theory would say that lists of random numbers don't have enough "evidence that I'm safe" (perhaps here, evidence that there is deeper structure like the structure in puns) and thus fall off the other side of the inverted U. But it would be interesting to see more about how these very abstract equivalents of "safe"/"danger" are built up. Without that it feels more tempting to say that funniness is fundamentally about surprise, perhaps as a reward for exploring things on the boundary of understanding, and that the social stuff was later built up on top of that.

I did put surprise on my list in Section 4.2.2, as one of the common sources of physiological arousal. So I don’t think we’re disagreeing on the narrow point that surprise can contribute to laughter.

Yeah, the correlation of surprise with danger (at least in the ancestral environment, although I think also today) is presumably why surprise tends to temporarily increase your heart rate. (I.e., surprising situations might call for immediate fight-or-flight type behaviors.)

I think my theory (surprise --> physiological arousal --> laughter) is a better fit than the direct “surprise --> laughter” alternative theory that you’re proposing (if I understand you). Two examples where I think my theory works and yours doesn’t are: Lists of random numbers, like you said (surprise is present [arguably, depending on your definition of “surprise”], physiological arousal is not, laughter is not), and kids chasing each other (no surprise, yes physiological arousal, often laughter).

There’s another kind of humor: a story or riddle that shows how superficially plausible reasoning leads to an unfortunate conclusion.  The old joke that you reference in footnote 7 is a perfect example of this. I think you might want to add this to your ingredient (A).  You also might want to explain why jokes stop being funny when you’ve heard them before.  This is pretty salient feature of humor which is not shared by e.g. tickling.

I got my theory of humor from Minsky (1980) “Jokes and the logic of the cognitive unconscious”, which I thought was very enlightening when I read it, many years ago. The abstract:

Freud’s theory of jokes explains how they overcome the mental “censors” that make it hard for us to think “forbidden” thoughts. But his theory did not work so well for humorous nonsense as for other comical subjects. In this essay I argue that the different forms of humor can be seen as much more similar, once we recognize the importance of knowledge about knowledge and, particularly, aspects of thinking concerned with recognizing and suppressing bugs — ineffective or destructive thought processes. When seen in this light, much humor that at first seems pointless, or mysterious, becomes more understandable.

Thanks! And thanks for the reference; I hadn’t seen that.

On my models, I can’t add what you said (“superficially plausible reasoning lead[ing] to an unfortunate conclusion”) to Ingredient (A), because that seems much more complicated than the types of innate signals that I think are in the hypothalamus and brainstem. The thing you said seems more like an abstraction, represented by latent variables in a world-model learned within one’s lifetime (see here, here).

But I can try to reconcile what you said with my existing Ingredient (A). So I’m looking through the list in  Section 4.2.2 of common conversational situations that can cause physiological arousal, and in the case of the anti-inductive reasoning joke, I would flag “surprise”, and maybe a little bit of “vicarious embarrassment” (because the speaker is revealing himself to be a moron), and also it’s not on the list but maybe a bit of pride / excitement upon getting the joke. 

why jokes stop being funny when you’ve heard them before

I’m figuring it’s the same reason that horror movies get less and less scary the more times you’ve seen them, and the same reason that the bunnies near my house have stopped hiding from my leashed pet dog.

Physiological arousal is metabolically expensive. So our brains have a system where, if we experience arousal in Situation X, and it eventually becomes apparent in hindsight that this arousal was never necessary for our safety, then a learning algorithm updates some brain connections such that, if we encounter a situation similar to Situation X in the future, it will be less likely to trigger arousal. (Cf. “extinction” in psych jargon.) So Ingredient (A) tends to go away upon repetition—the joke loses its “edge”. (There are exceptions; like maybe the very fact that the joke has been told so many times can become a new source of Ingredient (A). Then the joke can get funny again.)

Minsky, in his paper, posits that there is a system of censors in the brain, to prevent incorrect action.  He says that the sensation of humor is produced by the creation of a new censor, or the reinforcing of an existing one. It's not just learning; it's the learning of a particular kind of knowledge.  It's possible for the steering subsystem to reward phenomena in the learning subsystem, right?  In this case, the steering subsystem doesn't need to understand what the content of the censor is, just that there is one.  And it rewards the learning subsystem with a little jolt of reinforcement.  We call this kind of reinforcement "humor".

Anyway, this theory seemed plausible to me, for several reasons (I don't know how much of this is in the paper, and how much I came up with since then.)  

First, I think censors can be localized to the prefrontal cortex, or at least the frontal lobe.  Prefrontal damage or hypoxia makes you both rude and unsafe, suggesting that safety rules and politeness rules go in the same place, and that place is above the eyeballs.   

Second, optimality theory is a well-regarded theory of phonology (speech sound selection) where all possible pronunciations of a sentence advance through a list of rules until only one is left, which is then pronounced.  The theory of censors is an extension of this mechanism to action selection.  I'm not claiming that it's all of action selection; clearly we need positive, reward-anticipating mechanisms too.  But I think there's a place for a multitude of censors that are constantly watching, preventing you from making a boo-boo, in either action or reasoning.

Third, I've looked at a lot of jokes, and it's easy to see what the censor-worthy behavior is for any given joke.  Of course that might just be confirmation bias on my part.  

Fourth, it provides an explanation that explains why jokes stop getting funny due to repetition-- once the censor is established, there's no need for reinforcement.   That's why bathroom humor is hilarious when you're a little kid, but not when you've become a grownup and no longer need reinforcement for the "no potty talk" censor.  

Fifth, an explanation in terms of surprise or physiological arousal is over-general.  Here's an example of a story: "I was crossing the street in the middle of the block and forgot to look left.  Suddenly I realized there was a car careening toward me with screeching brakes.  Fortunately the car managed to  stop before I was struck, and everything was fine."  It's got surprise, it's got arousal, it's got sudden relief.  But it's not funny.

Thanks, that was another really helpful comment.

First off, I’m very sympathetic to a SoM-like picture where we learn a giant collection of abstract patterns of the form “When your thought pattern-matches to X, then it’s a bad idea to do Thing Y which you would otherwise do.” (Among other patterns.) That seems similar to what you’re calling “censors”, right?

I don’t particularly associate learning those patterns with laughter though. Like, I think back to when I was a kid practicing Olympiad-style math problems in high school: Early on I learned from experience “If you see a problem of this general form, try applying the Cauchy-Schwarz inequality”, and then somewhat later I would learn from experience an exception to that rule: “If you see a problem of this more specific form, then you’ll be inclined to try Cauchy-Schwarz, but don’t bother, it won’t work.” No laughing was involved during the process of learning that; it probably just looked like a kid sitting quietly in his room doing deliberate practice. Lots more examples like that: I know from experience hundreds of questions that I shouldn’t bother googling because I won’t find anything, and dozens of topics that I shouldn’t mention in the vicinity of certain relatives because they get very sensitive, and computer icons that I shouldn’t click in certain situations, and on and on. I don’t think any laughter was involved in learning or reinforcing any of those “censors”.

If the “creating or reinforcing censors” pattern isn’t sufficient for humor, is it necessary? Actually, maybe it is!! I wasn’t thinking this way last week when I wrote this post, but I was commenting here that maybe it’s impossible for a single conscious thought to create both Ingredient (A) an Ingredient (B). So instead, humor (and conversational-laughter) require thinking an Ingredient-(A) thought and an Ingredient-(B) thought in immediate succession, and maybe even flipping back and forth a couple times within the space of a second or two. And maybe the only way for that to happen in practice is that you’re thinking about a single “thing” but flipping back and forth between two different frames / analogies for that thing, one of which (call it “Frame 1”) triggers Ingredient (A) and the other of which (call it “Frame 2”) triggers Ingredient (B).

What does that have to do with the “censor” pattern? Well, during this process, your brain is incidentally learning / reinforcing the higher-level pattern that: “if something pattern-matches to Frame 1, then it’s possible to flip that thing to Frame 2, and vice-versa”. So in the future, you could be thinking a thought that seems to be a good plan, but this higher-level pattern jumps in and re-frames / re-analogizes it in a way that makes it feel like an aversive / bad plan. So if you’re laughing from humor or conversation, you’re incidentally learning or reinforcing a censor, I claim.

Fifth, an explanation in terms of surprise or physiological arousal is over-general.  Here's an example of a story: "I was crossing the street in the middle of the block and forgot to look left.  Suddenly I realized there was a car careening toward me with screeching brakes.  Fortunately the car managed to  stop before I was struck, and everything was fine."  It's got surprise, it's got arousal, it's got sudden relief.  But it's not funny.

When I think of that scenario, I feel like there’s no Ingredient (B). Or if there is, it’s not close enough in time to Ingredient (A) for the two to temporally overlap in the hypothalamus / brainstem. Like, I imagine almost getting killed jaywalking but the car stops inches from my legs. Standing safe on the sidewalk five seconds later, consciously I’d say “I am safe now”, but emotionally I don’t feel safe, or relaxed, at all. I would continue to feel extremely on-edge / jumpy / traumatized for at least minutes and possibly hours after that. Maybe the feeling gradually fades away and (B) gradually replaces it, but I would never have a juxtaposition of simultaneous (A) & (B) in my hypothalamus, I think.

I replied breifly before but I can't find it now, maybe cause I'm new. Also maybe cause it's 2am and I've just woken from a coffee bender induced nap. I feel I'm doing the conversation a disservice by writing on the fly, at 2am on my phone, but I feel compelled to say that I think humour (and laughter) are vital to the development and regulation of agi.

I love all of your reasoning regarding the causes of Laughter. Every argument seems sound to me and every counter argument I just read is welll answered already in your theory or by the person replying. In your search for the physiological mechanisms, have you considered that a particular region of the brain may not be the location? Laughter seems intrinsically linked to learning, and hence to the most basic neural proceses. Perhaps the mechanism is more a diatributed signalling process than any particular single structure.

One thing to consider about your model of humour is that all of the ingredients and nuances suggested by yourself and others for a and b, along with possibly c, are things that are the "sudden knowledge" in the quote I love about what laughter is.(please someone remeber where that is from for me!).

When our brains encounter knowledge, one expects the learning system of the brain to operate in a way that stimilates the persistence of that knowledge.The usual suspect here is the molecular signalling and feedback of the reward system. But what if that system becomes overloaded?

The startle/orienting process you describe, in all its forms, is knowledge being collected. The importance/significance is increased when danger is present, or when strongly held notions are upended. This significance should result in a stronger learning response than usual, and if the timing is right and the signal is strong enough, then a messaging or control molecule cascade or overabundance may ensue as inhibiton/depletion of the molecular signalling fails to keep up with production.

Tickling might not necessarily seem to be part of a learning/reward system. But the brain, especially oarts developed early in human(or mammalian) evolution, won't know that. To the brain, neural activity (novel neural activity in particular) is treated like learning, whether that activity is from sensory nerves stimulated physicaly, or brain neurons stimulated by thoughts and ideas.

Physical sensory nerves in ticklish areas might also provide a novel neuronal stimulation as the information from these sensory nerves overload the learning reward system. Ticklish areas, as well as being vulnerable (perhaps because they are vulneable) are possibly less frequently active and more abundant. Or perhaps the nature of the stimulation (tickling often needs to be done lightly to be effective) means these nerves can remain active longer/repeatedly since their potential isn't discharged or inhibited completely. Either way, if these nerves can provide more abundant, rapid or novel signalling than usual sensory input to the brain, they qualify as sudden knowledge.

Anything that can be considered knowledge of an abrupt and definitive nature, which produces a signal above a certain threshold, wil make us laugh. This threshold is highly individual, and changes as our perception of what is novel changes, as our worldview alters what startles us/how we orient, and even if we have drugged our poor brains with weed or alcahol.

Beauty works in a similar way, but Instead of a sudden and overwhelming stimulus being resolved to specific knowledge, it is the knowledge itself which is overwhelming. The resolution of a stumulus with a deep or strongly held knowledge produces the cascade here, causing an overwhelming reinforcement of held knowledge rather than new. But thats another two am bunch of dribble so I'll not say any more of how beauty works.

Understanding why and how laughter works (and beauty also) may be a key concept in getting an agi to develop curiosity. If an agi can be developed to be curious for curiosities sake, then that agi becomes not just a machine that can learn,, but one that becomes truly intelligent.

More importantly, concepts such as beauty and humour take an agi towards developing empathy and compassion. Despite the complexities and inconsitencies such 'emotional' traits bring, I think they are imperative for agi safety. So I think your musings ar far more than a distraction, and quite an interesting and important area to investigate.

Re: section 4.3.4 theories of humor

In my 2021 book Why Funny Is Funny, I introduce Clash Theory as a new 'grand theory of humor'. I believe it's much more precise than other theories, but I'm the creator of it so of course I'd say something like that that. The first five chapters are readable online. Click Read Sample (Kindle edition):