Self Awareness: The Last Frontier (V.S. Ramachandran)

You cannot tickle yourself—tickle requires a non-self, animate entity on the surface of your skin. This non-self, animate other is the most primitive social stimulus. Self-produced cutaneous stimuli are not ticklish because our nervous system cancels their effects, perhaps in the cerebellum. In the absence of such cancellation, we would be constantly tickling ourselves by accident.

The same mechanism that detects non-self, ticklish stimuli generates the sense of self. Although our sense of identity involves more than self/nonself discrimination, such a mechanism is at its foundation and a first step toward the evolution of personhood and the neurological computation of its boundaries.

Neurological conditions have shown that the self is not the monolithic entity it believes itself to be. It seems to consist of many components each of which can be studied individually, and the notion of one unitary self may well be an illusion. Consider the following disorders which illustrate different aspects of self:

• Out of body experiences: patients with right fronto-parietal strokes report floating out into space watching their body down below—undoubtedly contributing to the myth of disembodied souls. Left hemisphere strokes result in the feeling of a mysterious presence—a phantom twin—hovering behind the patient's left shoulder.

• Apotemnophilia: An otherwise completely normal person develops an intense desire to have his arm or leg amputated. The right parietal normally contains a complete internal image of the body. In these patients the part of the map corresponding to the affected limb is congenitally missing, leading to alienation of the limb.

• The patients are sometimes sexually attracted to amputees, We postulate that in " normal" individuals there is a genetically specified homunculus that serves as a template acting on limbic and visual areas to determine aesthetic preference for ones own body type. Hence pigs are attracted to pigs not people. If such an image is missing a limb, this may translate into an aesthetic preference toward an amputee.

• Transsexuality; A woman claims that for as far back as she can remember she felt she was a man trapped in a woman's body—even experiencing phantom penises and erections. Our ordinary notion of every person having a single sexual identity is called into question. It turns out there are at least four distinct aspects of sexuality; your external anatomy, your internal brain-based body image, your sexual orientation and your sexual identity—who you think others think of you as. Normally these are harmonized in fetal development but if they get uncoupled you become a transsexual person.

• A patient with a phantom arm simply watches arm of another person being touched. Astonishingly the patient feels the touch in his phantom. The barrier between him and others has been dissolved.

• Cotards syndrome; the patient claims he is dead and rejects all evidence to the contrary.

• Capgras delusion; the patient claims that his mother looks like his mother but is in fact an imposter. Other patients claim that they inhabit a house that's a duplicate of their real house. This highly specific delusion arises because the visual area in the brain is disconnected from emotional areas. So when our patient David sees his mother he recognizes her—along with the penumbra of memories linked to her. But no emotions and no jolt of familiarity is evoked so he rationalizes away his curious predicament saying she is an imposer. It is important to note that these patients are usually intelligent and mentally stable in most other respects. It is the selective nature of the delusion that makes it surprising and worth studying.

• In another disorder the patient, with damage to the anterior cingulate develops "akinetic mutism". He lies in bed fully awake and alert but cannot talk or walk—indeed doesn't interact in any way with people or things around him. Sometimes such patients wake up (when given certain drugs ) and will say "I knew what was going on around me but I simply had no desire to do anything ". It was if he had selective loss of one major attribute of the self — free will".

• Even odder is a phenomenon called "The telephone syndrome". The patient (I'll call him John) will display akinetic mutism—no visual consciousness—when seeing his (say) father in person. But if he receives a phone call from his father he suddenly becomes conscious and starts conversing with him normally. It's as if there are two Johns—the visual John who is only partially conscious and the auditory John (with his own self) who talks over the phone. This implies a degree of segregation of selves—all the way from sensory areas to motor output—that no one would have suspected.

We will now consider two aspects of self that are considered almost axiomatic. First its essentially private nature. You can empathise with someone but never to the point of experiencing her sensations. Second, it is aware of its own existence. A self that negates itself is an oxymoron. Yet both these axioms can fall apart in disease; without affecting other aspects of self. An amputee can literally feel his phantom limb being touched when he merely watches a normal person being touched. A person with Cotard's syndrome will deny that he exists; claiming that his body is a mere empty shell. Explaining these disorders in neural terms can help illuminate how the normal self is constructed.

To account for some of these syndromes we need to invoke mirror neurons. It's as if the neuron (more strictly the network of which the neuron is part) was using the visual input to do a sort of "virtual reality simulation" of the other persons actions—allowing you to empathize with her and view the world from her point of view. These neurons can not only help simulate other people's behavior but can be turned "inward"—as it were—to create second-order representations or metarepresentations of your own earlier brain processes. This could be the neural basis of introspection, and of the reciprocity of self awareness and other awareness.

I also suggest that although these neurons initially emerged in our ancestors to adopt another's allocentric visual point of view, they evolved further in humans to enable the adoption of another's metaphorical point of view. ("I see it from his point of view" etc.) This, too, might have been a turning point in evolution although how it might have occurred is deeply puzzling.

Despite all the pride that your self takes in its individuality and privacy, the only thing that separates you from me is a small subset of neural circuits in your frontal lobes interacting with mirror neurons. Damage these and you "lose your identity"—your sensory system starts blending with those of others.

Many otherwise inexplicable neuro-psychiatric symptoms may arise from flaws in these circuits leading to "you-me" confusion and impoverished ego-differentiation. Perhaps autistic children have a paucity of mirror neurons which would not only explain their poor imitation, empathy and 'pretend play" (which requires role-playing) but also why they sometimes confuse the pronouns I and You, and have difficulty with introspection.

Let us return to Cotards syndrome—the ultimate paradox of the self negating its own existence (sometimes claiming "I am dead", "I can smell my body rotting", etc.). Instead of emotions being disconnected from just visual centers, it is disconnected from all sensations and even memories of sensations. So the entire world becomes an imposter—unreal (not just the mother). Second, there may be a dissolution of the sense of self as being distinct from others (or indeed from the world). Lose the world and lose yourself—and it's as close to death as you can get. This is not a fully developed explanation by any means; I mention it only to indicate the style of thinking that we may need to explain these enigmatic syndromes.

Now imagine these same circuits become hyperactive as sometimes happens when you have seizures originating in the temporal lobes. The result would be an intense heightening of the patient's sensory appreciation of the world and intense empathy for all beings to the extent of seeing no barriers between himself and the cosmos—the basis of religious and mystical experiences. (You lose all selfishness and become one with God.) Indeed many of history's great religious leaders have had TLE. My colleague, the late Francis Crick, has suggested that TLE patients as well as priests may have certain abnormal transmitters in their brains that he calls "theotoxins". (He once told philosopher Pat Churchland that he had nothing against religion per se, so long as it was a private arrangement between consenting adults.)

I hasten to add that the involvement of the temporal lobes in mystical experiences does not in itself negate the existence of an abstract God, who, in Hindu philosophy, represents the supreme dissolution of all barriers. Perhaps the TLE patient has seen the truth and most of us haven't. I don't have TLE myself but have had personally had epiphanies when listening to a haunting strain of music, watching the aurora borealis, or looking at Jupiter's moons through a telescope. During such epiphanies I have seen eternity in a moment and divinity in all things. And, indeed, felt one with the Cosmos. There is nothing "true "or "false" about such experiences—they are what they are; simply another way of looking at reality.

Let us turn now to out-of-body experiences. Even a normal person—such as the reader—can at times adopt a "detached" allocentric stance toward yourself (employing something like mirror neurons) but this doesn't become a full blown delusion because other neural systems (e.g. inhibition from fontal structures and skin receptors) keep you anchored. But damage to the right fronto-parietal regions or ketamine anesthesia (which may influence the same circuits) removes the inhibition and you start leaving your body even to the extent of not feeling your own pain. You see your pain "objectively" as if someone else was experiencing it. Some such opossum-like detachment also occurs in dire emergencies when you momentarily leave yourself and watch your body being raped or mauled by a lion. This reflex is normally protective (lying still to fool predators) but a vestige of it in humans may manifest as "dissociative" states under conditions of extreme stress.

The purported "unity" or internal consistency of self is also a myth. A subset of patients who have additional damage to the "body image" representation in the right SPL claim that their paralyzed left arm doesn't belong to them. The patient may assert that it belongs to his father or spouse. (As if he had a selective "Capgras" for his arm). Such syndromes challenge even basic assumptions such as "I am anchored in this body" or "This is my arm". They suggest that "belongingness" is a primal brain function hardwired through natural selection because of its obvious selective advantage to our hominoid ancestors.

There appears to be almost no limit to this. An intelligent and lucid patient I saw recently claimed that her own left arm was not paralyzed and that the lifeless left arm on her lap belonged to her father who was "hiding under the table". Yet when I asked her to touch her nose with her left hand she used her intact right hand to grab and raise the paralyzed hand—using the latter as a "tool" to touch her nose! Clearly somebody in there knew that her left arm was paralyzed and that the arm on her lap was her own, but "she"—the person I was talking to—didn't know. I then lifted her "father's hand" up toward her, drawing attention to the fact that it was attached to her shoulder. She agreed and yet continued to assert it belonged to her father. The contradiction didn't bother her.

Her ability to hold mutually inconsistent beliefs seems bizarre to us but in fact we all do this from time to time. I have known many an eminent theoretical physicist who prays to a personal God; an old guy watching him from somewhere up there in the sky. I might mention that I have long known that prayer was a placebo; but upon learning recently of a study that showed that a drug works even when you know it is a placebo, I immediately started praying [allusion to Niels Bohr reply to a visitor who asked him if he really believed a horseshoe above his door brought him luck: "Of course not ... but I am told it works even if you don't believe in it."].

In the last decade there has been a tremendous resurgence of interest among neuroscientists in the nature of consciousness and self. The problem has been approached from many angles—ranging from single neuron electrophysiology to macroscopic brain anatomy (including hundreds of brain imaging studies). What has been missing, though, is what might be called "psycho-anatomy"; whose goal is to explain specific details of certain complex mental capacities in terms of equally specific activity of specialized neural structures. As an analogy, consider the discovery of the genetic code. Crick and Watson unraveled the double helix, and saw in a flash that the complementarity of the two strands of the helix is a metaphor of the complementarity of parent and offspring in heredity. In other words the structural logic of DNA dictates the functional logic of heredity. No such radical insight has emerged in neuroscience that would allow us to precisely map function on to structure.

One way of achieving this goal, as we have seen in this essay, might be to explore syndromes that lie at the interface between neurology and psychiatry. Given the inherent complexity of the human brain, it is unlikely that there will be a single climactic solution like DNA (although I don't rule it out). But there may well be many instances where such a synthesis is possible on a smaller scale and these may lead to testable predictions and novel therapies. They may even pave the way for a grand unified theory of mind of the kind physicists have been seeking in trying to unify gravitation, relativity and quantum mechanics.