Sensory Perception

[Angrboda]

Alien Hand Syndrome

The preceding two conditions both strike at the common-sense notion that each human being possesses a single, unified identity. Pure amnesia obliterates our sense of ourselves as continuous through time, chopping a person up into numerous evanescent selves, and the effects of callosal disconnection hint that there are multiple spheres of awareness lurking within our minds, which we usually do not notice because they normally communicate seamlessly with each other. Some experiments even seem to show that these spheres of awareness can have different desires from each other. However, there is another syndrome which demonstrates in a truly bizarre fashion that not only do these separate spheres of awareness exist, but that the divide runs far deeper than mere sensory perception. These discrete spheres within our brain can have different emotions and different thoughts - as is proven by the extraordinary condition called alien hand syndrome.

In Stanley Kubrick's classic black comedy Dr. Strangelove, the title character is afflicted with a bizarre disorder - one of his hands will not obey him. It attempts to make Nazi salutes at inappropriate times, even tries to strangle him on occasion, and he is often forced to use his other hand to restrain it. It has been said that truth is sometimes stranger than fiction, but in this case, truth is equally as strange as fiction, because Dr. Strangelove's malady really does exist.

"More than fifty years ago a middle-aged woman walked into the clinic of Kurt Goldstein, a world-renowned neurologist with keen diagnostic skills. The woman appeared normal and conversed fluently; indeed, nothing was obviously wrong with her. But she had one extraordinary complaint - every now and then her left hand would fly up to her throat and try to strangle her. She often had to use her right hand to wrestle the left hand under control.... She sometimes even had to sit on the murderous hand, so intent was it on trying to end her life." (Ramachandran 1998, p. 12)

The obvious explanation was that she was mentally disturbed and doing this to herself, and indeed that was the diagnosis of several physicians who had previously examined her. But Dr. Goldstein found no signs of hysteria or other mental disorders - it genuinely seemed as if her left hand had a will of its own - and so he proposed a radically different explanation. He theorized that the woman's right hemisphere (which controls the left side of the body, including the left hand) had "latent suicidal tendencies" (ibid.) In a normal person, the more rational left hemisphere would inhibit these and prevent them from being translated into action; but if this woman had suffered damage to her corpus callosum, these inhibitory messages could no longer be transmitted to the other half of her brain, and the right hemisphere would attempt to act on its irrational self-destructive urges.

Shortly after visiting Dr. Goldstein, the woman died (no, not from strangling herself). An autopsy confirmed the doctor's suspicions: she had suffered a stroke that had damaged her corpus callosum and severed the connection between the hemispheres, removing the brake her left hemisphere had put on the actions of her right.

Today, additional data has backed up Dr. Goldstein's explanation. It is now known that the right hemisphere is mainly responsible for producing and mediating negative emotions, such as anger and sadness; patients with right hemisphere damage often lose the ability to feel these emotions and become inappropriately cheerful and euphoric (this will be discussed in more detail below). Startling as it may seem, the woman's callosal disconnection had revealed that there were two separate spheres of consciousness within her mind that felt and desired completely different things.

One more question arises: If half this woman's brain had become suicidal, who or what was left over? What was the part of her that did not want to commit suicide and fought off the impulses of her "possessed" hand?

The answer, of course, was her rational left hemisphere, disconnected from the right and so unaffected by the negative emotions it was churning out. Since the left hemisphere controls language, it - and she - was able to express shock and dismay over the irrational behavior of the other side of her body. But what this implies for normal people is that we - the part that we think of as "ourselves" - is only the left hemisphere. That is the part that creates a narrative to explain our actions and communicates with the rest of the world. But all the while, there is another, separate consciousness dwelling within our heads - the silent right hemisphere. Unable to control language, it cannot make its presence known directly, and in any case it usually communicates with the left so seamlessly that we do not perceive it as a separate entity. But when callosal damage brings this mute, watching presence to the surface, the results can be astonishing.

Other cases of alien hand syndrome support this explanation. While this syndrome can happen in either hand, damage to the corpus callosum produces almost exclusively left alien hands. (Damage to the frontal lobes of the brain, which will be discussed in more detail later, can produce either a left or a right alien hand.) Furthermore, exactly as one would expect if AHS results from a disinhibition of the more emotionally volatile right hemisphere, alien hands are rarely helpful or pleasant. Instead, most of them perform actions ranging from the merely mischievous to the outright aggressive to the downright frightening. Frequently they do the opposite of what the consciously controlled hand intends. There are cases on record of alien hands that answer the phone and then refuse to surrender the receiver, that spill out drinks, that violently hurl objects at random. Sometimes a patient may open a drawer with his good hand only to have his alien hand close it; sometimes he may try to button up a shirt with one hand while the alien hand follows behind undoing the buttons. In one case on record, the alien hand attempted to tear up money (Feinberg 2001, p. 94-97).

Most disturbing of all, some alien hands are genuinely violent. Strangling actions, as described above, do occur. In another case on record, Dr. Michael Gazzaniga describes a patient whose left alien hand grabbed his wife and shook her violently, while his right hand tried to assist her in bringing the left under control. On another occasion, the doctor was visiting the same patient, playing horseshoes with him in his backyard, when the patient's left hand reached out and picked up an ax leaning against the side of the house.

"Because it was entirely likely that the more aggressive right hemisphere might be in control, I discretely left the scene - not wanting to be the victim for the test case of which half-brain does society punish or execute" (quoted in Feinberg 2001, p. 98).

As the good doctor astutely noted, there would be a real problem of who was responsible if his patient's alien hand had followed through on its seemingly ominous intentions. But that problem would not be limited to merely mortal agents of justice. How would God judge such a case?

The dualist must answer the question of how all of this is compatible with the existence of the soul. Do our souls reside only in our left hemispheres? Then who or what lives in the right? Or would dualists claim that the single, unified soul can somehow become fractured, split into two distinct consciousnesses, by damage to the physical brain?

— Ebon Musings, The Atheism Pages:

Is it likely that both hemispheres have the same "perception" of their half of the perceptual field? Different? Incommensurate?


See also, anosognosia (paralysis denial) and temporary reversal of anosognosia via treatment of ear canal with cold water; comments: (ibid.)

And a non-dualistic theory of the workings of the human mind can offer just such an explanation. Observing that anosognosia almost exclusively results from right-hemisphere damage, Dr. Ramachandran has proposed that the two halves of our brain serve two different roles in regard to our worldviews. His hypothesis is that the left hemisphere's job is to create a coherent perspective: to sort through the data it constantly receives from the senses and integrate it all into a consistent worldview. But when inconsistent data arrives - information that conflicts with what we already know or believe - it must be handled. One option, of course, is to completely tear down the existing belief structure and start over again; but if we did this for every minor discrepancy we encountered, it would be impossible to function in the world. Therefore, the left hemisphere functions as a preserver of the status quo, defending a person's belief system by discounting contradictory evidence or force-fitting it into the existing framework. The right hemisphere, by contrast, is hypothesized to be a "devil's advocate," searching for major inconsistencies and problems with the status quo and forcing a reevaluation of preexisting beliefs if enough inconsistencies turn up. (One possible explanation for why the cold-water treatment works is that it may stimulate nerves leading into the right hemisphere.)