Sometimes, indeed, the patient did become specific in his replies.
But far more representative of the data as a whole is the patients' persistence under questioning that these experiences could not be called memories.
Because of this, and because of the general absence of personal active images, which are the usual kind of memories that we have, I suggest that the conclusions of Penfield and Perot are incorrect. These areas of the temporal lobe are not "the brain's record of auditory and visual experience," nor are they its retrieval, but combinations and amalgamations of certain aspects of that experience. The evidence does not, I think, warrant the assertion that these areas "play in adult lives some role in the subconscious recall of past experience, making it available for present interpretation." Rather the data lead away from this, to hallucinations that distill particularly admonition experiences, and perhaps become embodied or rationalized into actual experiences in those patients who reported them on being questioned.
3. That the Two Hemispheres Can Behave Independently In our brain model of the bicameral mind, we have assumed that the god part and the man part behaved and thought somewhat independently. And if we now say that the duality of this
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ancient mentality is represented in the duality of the cerebral hemispheres, is this not personifying parts of the brain without warrant? Is it possible to think of the two hemispheres of the brain almost as two individuals, only one of which can overtly speak, while both can listen and both understand?
The evidence that this is plausible comes from another group of epileptics. These are the dozen or so neurosurgical patients who have undergone complete commissurotomy, the cutting down the midline of all interconnections between the two hemispheres.10
This so-called split-brain operation (which it is not — the deeper parts of the brain are still connected) usually cures the otherwise untreatable epilepsy by preventing the spread of abnormal neural excitation over the whole cortex. Immediately after operation, some patients lose speech for up to two months, while others have no problem whatever — no one knows why. Perhaps each of us has a slightly different relationship between our hemispheres. Recovery is gradual, all patients showing short-term memory deficits (perhaps due to the cutting of the small hippocampal commissures), some orientation problems, and mental fatigue.
Now the astonishing thing is that such patients after a year or so of recovery do not feel any different from the way they felt before the operation. They sense nothing wrong. At the present time they are watching television or reading the paper with no complaints about anything peculiar. Nor does an observer notice anything different about them.
But under rigorous control of sensory input, fascinating and important defects are revealed.
10 The literature on these patients of Joseph E. Bogen is still expanding. I would recommend his classical papers, particularly "The other side of the brain, II: An appositional mind," Bulletin of the Los Angeles Neurological Society, 1969, 34 (3) : 135-162. For a discussion by one of the pioneers in hemispheric research, R. W.
Sperry, "Hemisphere Deconnection and Unity in Conscious Awareness," American Psychologist, 1968, 23: 723-733. And for a readable account by the man whose in-genuity devised ways of testing these patients, read Michael Gazzaniga's The Bisected Brain (New York: Appleton-Century-Crofts, 1970).
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As you look at anything, say, the middle word of this line of print, all the words to the left are seen only by the right hemisphere, and all the words to the right only by the left. With the connections between the hemispheres intact, there is no particular problem in co-ordinating the two, although it really is astonishing that we can read at all. But if you had your hemispheric connections cut, the matter would be very different. Starting at the middle of this line, all the print to your right would be seen as before and you would be able to read it off almost as usual. But all the print and all the page to your left would be a blank. Not a blank really, but a nothing, an absolute nothing, far more nothing than any nothing you can imagine. So much nothing that you would not even be conscious that there was nothing there, strange as it seems. Just as in the phenomenon of the blind spot, the 'nothing' is somehow 'filled in', 'stitched together', as if nothing were wrong with nothing. Actually, however, all that nothing would be in your other hemisphere which would be seeing all that 'you' were not, all the print to the left, and seeing it perfectly well. But since it does not have articulated speech, it cannot say that it sees anything. It is as if 'you' — whatever that means — were 'in' your left hemisphere and now with the commissures cut could never know or be conscious of what a quite different person, once also 'you', in the other hemisphere was seeing or thinking about. Two persons in one head.
This is one of the ways these commissurotomized patients are tested. The patient fixates on the center of a translucent screen; photographic slides of objects projected on the left side of the screen are thus seen only by the right hemisphere and cannot be reported verbally, though the patient can use his left hand (controlled by the right hemisphere) to point to a matching picture or search out the object among others, even while insisting vocally that he did not see it.11 Such stimuli seen by the right nondomi-11 M. S. Gazzaniga, J. E. Bogen, and R. W. Sperry, "Observations on visual perception after disconnection of the cerebral hemispheres in man," Brain, 8: 221-236, 1965.
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nant hemisphere alone are there imprisoned, and cannot be ‘told’
to the left hemisphere where the language areas are because the connections have been cut. The only way we know that the right hemisphere has this information at all is to ask the right hemisphere to use its left hand to point it out — which it can readily do.
If two different figures are flashed simultaneously to the right and left visual fields, as, for example, a “dollar sign” on the left and a “question mark” on the right, and the subject is asked to draw what he saw, using the left hand out of sight under a screen, he draws the dollar sign. But asked what he has just drawn out of sight, he insists it was the question mark. In other words, the one hemisphere does not know what the other hemisphere has been doing.
Again, if the name of some object, like the word ‘eraser’, is flashed to the left visual field, the subject is then able to search out an eraser from among a collection of objects behind a screen using only the left hand. If the subject is then asked what the item is behind the screen after it has been selected correctly, ‘he’
in the left hemisphere cannot say what the dumb ‘he’ of the right hemisphere is holding in his left hand. Similarly, the left hand can do this if the word ‘eraser’ is spoken, but the talking hemisphere does not know when the left hand has found the object.
This shows, of course, what I have said earlier, that both hemispheres understand language, but it has never been possible to find out the extent of language understanding in the right hemisphere previously.
Further, we find that the right hemisphere is able to understand complicated definitions. Flashing “shaving instrument”
onto the left visual field and so into the right hemisphere, the left hand points to a razor, or with “dirt remover” to soap, and with