Mar 27, 2011
The scientific approach to self-help suggests that a better understanding of who we are can help us achieve happiness and other goals. Most centrally, it will be helpful to understand our brains, because it is our brains that generate happiness and goals.
In particular, I'd like to explore the neuroscience of pleasure and desire. Today's post covers the neuroscience of pleasure; the next post will cover the neuroscience of desire. After each post I'll consider some of the implications for self-help. In a later post, I'll consider how this research can inform the pursuit of Friendly AI.
The last decade has seen the arrival of affective neuroscience: the study of the neural mechanisms behind emotion, including pleasure and desire.1 Most questions remain unanswered, and experts disagree on many specifics,2 but there are some things we can state with confidence. We begin with the reward system in the brain.
Unfortunately, the interaction between these components is extraordinarily complex, and many puzzles remain.5
I'll share two examples of our ignorance. First: pleasure electrodes. For decades, it was thought that electrical stimulation of certain structures caused pleasure, because rats and humans would self-administer this stimulation hundreds or thousands of times each hour if allowed to do so.6 But a careful reading of the transcripts reveals the causation of wanting, not liking. Sometimes, the cause was even an unpleasant nervousness.7 Though, there are a few exceptions where liking was produced.8
Second: dopamine. For decades, experts thought dopamine was 'the pleasure chemical'.9 But this is probably false.10 Lack of dopamine does not impair 'liking' reactions.11 And in humans, perceived pleasure is not reduced by loss of dopamine.12 Dopamine has a big role in wanting, instead.13
Today we focus on 'liking' or pleasure.
Thoughts and sensations are not intrinsically pleasurable. Rather, the reward system must paint them with a 'hedonic gloss' to make them 'liked'.14 Food and sex are reliably pleasurable for obvious Darwinian reasons.15 These 'fundamental pleasures' use the same brain structures as 'higher-order pleasures' like social pleasures, art, money, and altruism.16
The basic structures which produce pleasure are shared by other mammals (for Darwinian reasons), and other mammals exhibit liking processes in the brain.17 It's not clear how similar their subjective experience of pleasure is to our own, though. Humans do have unique cognitive, representational and 'savoring' capacities,18 among others.
Much research concerns 'hedonic hotspots' in the brain. A hedonic hotspot might be a necessary cause of pleasure (pleasure doesn't occur without it; e.g. the ventral pallidum), a sufficient cause of pleasure (if activated, pleasure occurs; e.g. the nucleus accumbens), or it may code for pleasure (its activation correlates with pleasure, but might be either a cause or effect of pleasure, or both; e.g. the orbitofrontal cortex and ventral pallidum). A substrate may play multiple roles, or it may code without causing, or it may be a sufficient cause without being a necessary cause.19
We know thousands of specific things about pleasure and the reward system, but we don't yet understand pleasure on a systems level. We don't know how to integrate these thousands of bits of information into a cohesive theory of how pleasure works.
Many have tried, of course. Here is Tim Schroeder's attractively simple theory of pleasure:
To be pleased is (at least) to represent a net increase in desire satisfaction relative to expectation; to be displeased is to represent a net decrease in desire satisfaction relative to expectation. Intensity of pleasure or displeasure represents degrees of change in desire satisfaction relative to expectations.20
But this is too simple. Though pleasure often results from experiencing more satisfaction than expected, there are many other sources of pleasure,21 and pleasure can occur in animals that lack representational capacities or expectations, for example anecephalic infants and animals with most of their brains removed.22
Among neuroscientists, there are many overlapping theories of pleasure, which are often not mutually exclusive.23 Rather than survey them all, let me jump to the self-help advice: what can brain science teach us about pleasure and how to get more of it?
The neuroscience of pleasure is most useful when designing new drugs or performing neurosurgery, but there are a few self-help recommendations we can draw from the field:
This is a short list, but additional self-help recommendations can be gleaned after we build on this knowledge to discuss the neuroscience of desire, which we will cover next.
1 LeDoux & Phelps (2000); Berridge (2003a); Davidson et al. (2003); Damasio (2004); Rolls (2005); Feldman & Wager (2006); Kringelbach (2005); Kringelbach & Berridge (2009a, 2009b).
2 Kringelbach et al. (2009).
3 Berridge & Kringelbach (2008); Berridge et al. (2009); Berridge (1996); Berridge & Robinson (1998); Pecina et al. (2003); Camerer (2006); Kringelbach & Berridge (2010b). Some experts will talk as if there is no such thing as unconscious pleasure (Kringelbach et al. 2009), but this is only a manner of speaking adopted to respect the folk understanding of conscious pleasure, for they acknowledge the same unconscious hedonic processes that other researchers do (Winkielman & Berridge 2004; Winkielman et al. 2005; Schooler & Mauss 2009). Likewise, though ever researcher may not use the liking / wanting / learning scheme, I haven't found any major expert who disagrees with the minimal factual claims presupposed by that scheme. Experts agree that pleasure, motivation, and learning are distinct components of the reward system in the brain.
4 The neural processes that apply the 'hedonic gloss' to sensations and cognitions seem to be a particular pattern of excitation of neurons in a hedonic hotspot in the ventral pallidum (Tindell et al. 2005; Aldridge & Berridge 2009), though other brain structures may play a role as well, in particular the nucleus accumbens (Smith et al. 2001), the orbitofrontal cortex (Kringelbach 2009), and perhaps the perigenual anterior cingulate cortex (Schroeder 2004, ch. 3). Commonly measured 'surface' pleasure reactions are (1) subjective report in humans, and (2) particular facial expressions in human adults, human infants, chimpanzees, and rats (Smith et al. 2005). See videos here.
5 Baldo & Kelley (2007); Balleine & Kilcross (2006); Balleine et al. (2007); Beaver et al. (2006); Burke et al. (2009), Di Chiara & Bassareo (2007); Evans et al. (2006); Everitt & Robbins (2005); Izard (2007); Kuhn & Koob (2010); Panksepp (2007); Salamone et al. (2007); Schultz (2006); Stoeckel et al. (2008); Van Leijenhorst et al. (2010); Volkow et al. (2006); Voon et al. (2010); Wise (2006); Kringelbach & Berridge (2010a).
6 Delgado (1969); Heath (1972); Sem-Jacobsen (1976).
7 Berridge (2003b); Pecina et al. (2006); Smith et al. (2009).
8 Morgan et al. (2006).
9 Hoebel et al. (1999); Shizgal (1999); Wise & Bozarth (1985).
10 Smith et al. (2009); Berridge (2007); Robinson & Berridge (2003).
11 Berridge & Robinson (1998); Berridge et al. (1989); Robinson et al. (2005); Pecina et al. (1997).
12 Sienkiewicz-Jarosz et al. (2005); Brauer et al. (2001); Leyton et al. (2005); Leyton (2009).
13 Berridge (2007).
14 Frijda (2006, 2009); Aldridge & Berridge (2009); Ryle (1954).
15 Cabanac (2009); Kringelbach (2005, 2009); Rolls (2005); Schulkin (2004).
16 Kringelbach (2005, 2009); Pecina et al. (2006); Small et al. (2001); Gottfried (2009); Kahneman et al. (2004).
17 Steiner et al. (2001); Berridge (2000); Kringelbach (2008, 2009); Smith et al. (2009); Calder et al. (2007).
18 Barrett et al. (2007); Frijda (2006); Frijda & Sundarajan (2007); Gilbert & Wilson (2007).
19 Berridge & Kringelbach (2008); Smith et al. (2009).
20 Schroeder (2004), p. 94.
21 Smith et al. (2009); Kringelbach & Berridge (2009b).
22 Steiner (1973); Steiner et al. (2001); Goltz (1892); Miller & Sherrington (1915); Grill & Norgren (1978). It must be noted that my summary is a bit unfair to Schroeder: Schroeder is offering a theory only of conscious pleasure, which may indeed require the representational capacities unneeded for unconscious 'liking.' Still, it remains the case that there seem to be many other causes and implementations of pleasure than representations of a positive difference between actual desire satisfaction and expected desire satisfaction. But Schroeder's theory is not, as far as I can tell, decisively falsified by the data.
23 See Dickinson & Balleine (2009) for a comparison of theories. Some leading theories are: the somantic marker hypothesis by Damasio (1996), the hedonic interface theory by Dickinson & Balleine (2009), the common currency theory of Cabanac (1992), and the multiple-components theories of Berridge, Kringelbach, and others: see Berridge & Kringelbach (2008); Kringelbach (2008).
24 Smith et al. (2009); Tindell et al. (2005); Smith et al. (2007); Berridge et al. (2009).
25 Smith et al. (2009); Dickinson & Balleine (2009).
26 For example, Damasio (1994), p. 263.
27 Burke et al. (2009); Aldridge & Berridge (2009).
28 Berns et al. (2006).
29 Gard et al. (2006).
30 Green et al. (2009).
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