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tion. But in bicameral men, this was volition. Another way to say it is that volition came as a voice that was in the nature of a neurological command, in which the command and the action were not separated, in which to hear was to obey.
C H A P T E R 5
The Double Brain
WHAT HAPPENS in the brain of a bicameral man? Anything as important in the history of our species as a completely different kind of mentality existing only a hundred generations ago demands some statement of what is going on physiologically.
How is it possible? Given this profoundly subtle structure of nerve cells and fibers inside our skulls, how could that structure have been organized so that a bicameral mentality was possible?
This is the great question of the present chapter.
Our first approach to an answer is obvious. Since the bicameral mind is mediated by speech, the speech areas of the brain must be concerned in some important way.
Now in discussing these areas, and throughout this chapter, and indeed in the rest of this essay, I shall be using terms suitable only to right-handed people, in order to avoid a certain clumsi-ness of expression. Thus, it is the left cerebral hemisphere of the brain, controlling the right side of the body, which in right-handed people contains the speech areas. It is therefore commonly called the dominant hemisphere, while the right hemisphere, controlling the left side of the body, is commonly called the nondominant. I shall be speaking as if the left hemisphere were dominant in all of us. Actually, however, left-handed persons have a variety of degrees of lateral dominance, some being completely switched (the right hemisphere doing what the left usually does), others not, and still others with
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T h e three speech areas of the left hemisphere have different functions and values. T h e supplementary motor area is mostly involved in articulation; Broca's area in articulation, vocabulary, inflection, and grammar; and Wernicke's area in vocabulary, syntax, meaning, and understanding speech.
mixed dominance. But being exceptional, only 5 percent of the population, they can be left out of the present discussion.
The speech areas then are three, all on the left hemisphere in the great majority of mankind.1 They are: (I) the supplementary motor cortex, on the very top of the left frontal lobe, removal of which by surgery produces a loss of speech which clears up in several weeks; (2) Broca's area, lower down at the back of the left frontal lobe, the removal of which produces a loss of speech which is sometimes permanent and sometimes not; and (3) Wernicke's area, chiefly the posterior part of the left temporal lobe with parts of the parietal area, any large destruction of 1 I am here following the late Wilder Penfield and Lamar Roberts, Speech and Brain-Mechanisms (Princeton: Princeton University Press, 1959), the traditional authority although some of it is out of date in the present explosion of knowledge in this area.
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which after a certain age produces a permanent loss of meaningful speech.
It is thus Wernicke's area that is the most indispensable to normal speech. As we might expect, the cortex in Wernicke's area is quite thick with large, widely spaced cells, indicating considerable internal and external connections. While there is some disagreement as to its precise boundaries,2 there is none about its importance to meaningful communication.
Of course it is extremely hazardous thinking to isomorphize between a conceptual analysis of a psychological phenomenon and its concomitant brain structure, yet this is what we cannot avoid doing. And among these three areas on the left hemisphere, or even in their more subtle interrelationships, it is difficult to imagine a duplication of some speech function to the extent and separation which my theory of the bicameral mind would demand.
Let us sit down with this problem a moment. Speech areas all on the left side. Why? One intriguing puzzle which has long fascinated me and anyone else who has considered the evolution of all this is why language function should be represented in only one hemisphere. Most other important functions are bilaterally represented. This redundancy in everything else is a biological advantage to the animal, since, if one side is injured, the other side can compensate. Why then was not language? Language, that most urgent and significant of skills, the pre-emptory and exigent ground of social action, the last communicant thread on which life itself in the post-glacial millennia must often have depended! W h y was not this without-which-nothing of human culture represented on both hemispheres?
The problem drifts off into even more mystery when we remember that the neurological structure necessary for language 2 Joseph Bogen with his usual helpfulness has taken the time to point out to me the slipperiness of the evidence for just what regions are to be included in Wernicke's area. I am also indebted to my former student, Stevan Hamad, for invaluable discussion on many of these issues.
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exists in the right hemisphere as well as the left. In a child, a major lesion of Wernicke's area on the left hemisphere, or of the underlying thalamus which connects it to the brainstem, produces transfer of the whole speech mechanism to the right hemisphere. A very few ambidextrous people actually do have speech on both hemispheres. Thus the usually speechless right hemisphere can under certain conditions become a language hemisphere, just like the left.
And a further range of the problem is what did happen in the right hemisphere as the aptic structures for language were evolving in the left? Just consider those areas on the right hemisphere corresponding to the speech areas of the left: what is their function? Or, more particularly, what is their important function, since it must have been such to preclude its development as an auxiliary speech area? If we stimulate such areas on the right hemisphere today, we do not get the usual "aphasic arrest"
(simply the stopping of ongoing speech) which occurs when the normal language areas of the left hemisphere are stimulated.
And because of this apparent lack of function, it has often been concluded that large portions of the right hemisphere are simply unnecessary. In fact, large amounts of right hemisphere tissue, including what corresponds to Wernicke's area, and even in some instances the entire hemisphere, have been cut out in human patients because of illness or injury, with surprisingly little deficit in mental function.
The situation then is one where the areas on the right hemisphere that correspond to the speech areas have seemingly no easily observable major function. Why this relatively less essential part of the brain? Could it be that these silent 'speech' areas on the right hemisphere had some function at an earlier stage in man's history that now they do not have?
The answer is clear if tentative. The selective pressures of evolution which could have brought about so mighty a result are those of the bicameral civilizations. The language of men was
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involved with only one hemisphere in order to leave the other free for the language of gods.
If so, we might expect that there would have to be certain tracts by which the bicameral voices would relate between the right nondominant temporal lobe and the left. The major interconnection between the hemispheres is of course the huge corpus callosum of over two million fibers. But the temporal lobes in men have their own private callosum, so to speak, the much smaller anterior commissures. In rats and dogs, the anterior commissures connect the olfactory parts of the brain. But in men, as seen in my rather imprecise sketch, this transverse band of fibers collects from most of the temporal lobe cortex but particularly the middle gyrus of the temporal lobe included in Wernicke's area, and then squeezes into a tract only slightly more than one eighth of an inch in diameter as it plunges over the amygdala across the top of the hypothalamus toward the other temporal lobe. Here then, I suggest, is the tiny bridge across which came the directions which built our civilizations and founded In ancient times, what corresponds to Wernicke's area on the right hemisphere may have organized admonitory experience and coded it into 'voices' which were then 'heard' over the anterior commissure by the l e f t or dominant hemisphere.