Part of the felt sense of self is perceiving oneself as having a body, or being embodied, or being in one’s body.

Here, I don’t want to talk about embodiment as opposed to “being in one’s head” (the head is part of the body, after all) but embodiment in the sense that you feel like there’s a “locus of identity”, a “you”, somewhere within the boundaries of your body, as opposed to feeling like you’re floating outside yourself or like you don’t exist at all.

People can have these unusual “disembodied” perceptions during near-death experiences, while under the influence of dissociative drugs, or in dissociative disorders, or in some meditative states.

How does this relate to consciousness? A disembodied state is not total unconsciousness — the person can still describe having had an experience — but it’s not the usual relationship of self, body, and experience, where people feel there’s a “me” on the “inside” of the body, and an “outside world” surrounding me.

So, we can ask: what is going on in the brain when this ordinary “inside self/outside world” relationship is disrupted? Are there neurological commonalities between different types of such disruption? How does the brain construct that inside/outside relationship?

Autoscopy and Out-of-Body Experiences

An out-of-body experience is just what it sounds like: the perception that one is floating outside the body, e.g. seeing the world as though looking down from above.

Autoscopy is the related phenomenon of seeing your own body as if “from the outside”, or seeing a “double” of your body. It’s possible to experience autoscopic phenomena while still feeling that you’re “inside your own body” and the “double” is the illusion.1

In out-of-body experiences, there are frequently vestibular sensations (flying, floating, rotating) as well as visual perspective distortions (seeing the world as though from an angle that would be impossible from within your own body).

These experiences can occur in epilepsy, particularly when seizures affect the angular gyrus2 in the inferior parietal lobule, or other regions near the temporoparietal junction.3 Electrical stimulation in the same location as the seizures can, in some patients, recreate the out-of-body experience.

In one case, a patient who didn’t ordinarily have out-of-body experiences consistently had them when electrically stimulated in the angular gyrus and nearby supramarginal gyrus (as part of treatment for tinnitus.) He felt he was about 50 cm behind his body and off to the left.4 Another patient undergoing surgery for a brain tumor repeatedly had out-of-body experiences when stimulated subcortically near the temporo-parietal junction — “she felt as if she floated just below the ceiling and saw her own body lying on the operating table”.5

One speculation is that out-of-body experiences are the result of discordant information from different sensory modalities (visual, tactile, vestibular, and proprioceptive). The temporal-parietal junction that is so often disturbed in out-of-body experiences is a major site of multisensory integration.6 Accordingly, patients with vestibular disorders are more likely (14% vs 5%) to have had an out-of-body experience than controls with no history of dizziness.7

Ketamine, a dissociative NMDA-inhibiting drug, was by far the most correlated recreational drug with out-of-body experiences in a sample of recreational drug users.8 A statistical study of ketamine users supports the theory that the causality goes from “illusory movement” (the feeling that you are moving when you’re not) sometimes causing “out-of-body feelings” (the kinaesthetic sense of not being inside one’s own body), which in turn sometimes causes “out-of-body autoscopy” (visually seeing one’s own body as if from the outside.) Illusory movement is the most common of the three phenomena, and out-of-body autoscopy is the least common.9

Autoscopic hallucinations, like out-of-body experiences, are also associated with seizures or brain lesions, but sometimes in different places than the ones associated with out-of-body experiences, like the occipital lobes, which are sites of visual perception.101112

This localization makes prima facie sense — you get purely visual hallucinations of a “double” when there’s damage to visual regions of the brain, while you get kinaesthetic or multisensory “out of body” sensations when vestibular and sensory-integration regions are disrupted.

This also corresponds well to the theory that the feeling of an “embodied self” emerges from predictable and coherent multisensory integration; when there’s illusory motion, dizziness, or other sensations inconsistent with a fixed or predictable location in space, people are more likely to experience their “locus of identity” drifting outside the physical body.

Ipseity Disturbance and Depersonalization

It’s possible to have a sensation of detachment, strangeness, or remoteness from one’s own body or self; not quite an out-of-body experience but still a quasi-perceptual abnormality.

Some quotes from two schizophrenic patients13:

“In general, I didn’t have a sense of my body anymore; this completely vanished at some time. My face became increasingly strange to me, as it still is today. My voice, too, because I talked much less. Just an extreme self-estrangement.”

“I feel as if I am sitting on some distant planet and there is somehow a camera in my head and those images are sent there. As if I am completely far away from here, where I am sitting right now.”

“For me it was as if my eyes were cameras, and my brain would still be in my body, but somehow as if my head were enormous, the size of a universe, and I was in the far back and the cameras were at the very front. So extremely far away from the cameras. And I walk, and I look around … and I’m dizzy, and all is like a machine …”

Parnas and Handest observed that in early or prodromal schizophrenia, before “positive symptoms” like hallucinations or delusions form, there’s often an experience of dissociation or depersonalization, which they term “ipseity disturbance” — not feeling like oneself.14

Some more quotes from patients:

“my first personal life is lost and is replaced by a third-person perspective”.

“I am no longer myself (. . .) I feel strange, I am no longer in my body, it is someone else; I sense my body but it is far away, some other place. Here are my legs, my hands, I can also feel my head, but cannot find it again. I hear my voice when I speak, but the voice seems to originate from some other place…One might think that my person is no longer here (. . .) I walk like a machine; it seems to me that it is not me who is walking, talking, or writing with this pencil. When I am walking, I look at my legs which are moving forward; I fear to fall by not moving them correctly.”

“I feel a simultaneous implosion and explosion” (as though his body was simultaneously very small and very large.)

“it feels as if my thoughts were slightly behind my skull”… her “point of perspective” was felt “as if displaced some centimetres behind.”

“something in me has become inhuman,” “no contact to his body,” “feels empty”.

The authors hypothesize that certain classic schizophrenic hallucinations or delusions (like thought insertion) are simply consequences of the loss of the feeling of selfhood.

Other delusions, regardless of their bizarre details (reincarnated extraterrestrials and the like), may be interpreted as a process of re-personalization, where the patient hits on some magical/metaphysical thing as a solution to restore the perception of “aliveness”, “realness”, “meaningfulness”, “specialness” that was lost in the prodromal period.

Depersonalization is defined in the DSM as feeling detached from, or like an outside observer of, one’s own mental or bodily processes. People who meet criteria for depersonalization disorder, in a sample of 117 cases, were particularly likely to agree with statements like “my surroundings feel unreal”, “I’m looking at the world through a fog”, or “my body does not belong to me.”15

Some quotes from depersonalization patients16:

““It is as if the real me is taken out and put on a shelf or stored somewhere inside of me. Whatever makes me me is not there. It is like an opaque curtain . . . like going through the motions and having to exert discipline to keep the unit together.”

“I am disconnected from my body. It is as if my body is not there.”

“a feeling of unreality and distance, like I am a spectator of my own movements and of what is going on.”

Patients with either depersonalization disorder or schizophrenia might experience perceptions that their thoughts are not their own (“Thoughts running through his brain again seemed somehow foreign”), that their self is gone (“as if I ceased to exist”), or that their self is somehow unreal or false (“like an actor in a play”, “going through the motions”).17

Despite this subjective feeling of disembodiment or unreality, patients with depersonalization symptoms have intact interoception — they are just as accurate and confident as healthy controls at perceiving their own heartbeats.18

Depersonalization can occur in epilepsy, especially temporal lobe epilepsy, which often coincides with feelings of unreality before and after the seizure. Temporal lobe seizures can go with feelings that one “isn’t there”, “isn’t real”, “is in a dream”, “loses the sense of oneself” or “goes outside oneself.” Out of 47 cases of depersonalization associated with neurological disorders, epilepsy is by far the most common, and in many cases surgical treatment for epilepsy improves the depersonalization symptoms.19

I don’t see a great deal of consistency or clarity across accounts of neural correlates of depersonalization. Some fMRI studies point to decreased activity in the insula20, others to the anterior cingulate cortex21, in depersonalization; an epilepsy study associates depersonalization with activity in the dorsal premotor cortex;22 a PET study finds reduced metabolic activity in the superior and middle temporal gyri in depersonalization23; etc. It’s possible that depersonalization symptoms are too diverse to have a common cause in the brain, or that they aren’t localized anatomically at all — or it could just be that this particular research literature hasn’t successfully come to replicable conclusions yet.

Nonetheless, what we do know is that people can lose the “sense of being oneself” that most of us take for granted, and that this is usually distressing. Depersonalization or “ipseity disturbance” symptoms generally come with an unpleasant sense of falsity, meaninglessness, or troubling strangeness.

They’re not clearly associated with sensory deficits the way out-of-body experiences, rubber hand illusions, neglect, asomatognosia, or somatoparaphrenia are. Disturbances in the “sense of self” might be higher-order or more abstract than sensory processing per se, even though they do involve subjective perceptual distortions (in particular distortions of size, distance, and solidity/boundaries).

In further posts I’ll try to get a sharper picture of what’s going on in the “sense of self”, and also look at what underlies perceptions of agency or volition.