1.5. 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 clumsiness of expression. Thus, it is the left cerebral hemisphere of the brain, controlling the right side of the body, which in righthanded 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, lefthanded 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 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 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! Why 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 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 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 the world’s religions, where gods spoke to men and were obeyed because they were human volition.³

There are two forms in which this hypothesis can be specified.

The stronger form, and the one I favor because it is simpler and more specific (and thus more easily verified or disconfirmed by empirical investigation), is that the speech of the gods was directly organized in what corresponds to Wernicke’s area on the right hemisphere and ‘spoken’ or ‘heard’ over the anterior commissures to or by the auditory areas of the left temporal lobe. (Note how I can only express this metaphorically, personifying the right temporal lobe as a person speaking or the left temporal lobe as a person listening, both being equivalent and both literally false.) Another reason I am inclined to this stronger form is its very rationality in terms of getting processed information or thought from one side of the brain to the other. Consider the evolutionary problem: billions of nerve cells processing complex experience on one side and needing to send the results over to the other through the much smaller commissures. Some code would have to be used, some way of reducing very complicated processing into a form that could be transmitted through the fewer neurons particularly of the anterior commissures. And what better code has ever appeared in the evolution of animal nervous systems than human language? Thus in the stronger form of our model, auditory hallucinations exist as such in a linguistic manner because that is the most efficient method of getting complicated cortical processing from one side of the brain to the other.

The weaker form of the hypothesis is more vague. It states that the articulatory qualities of the hallucination were of left hemisphere origin like the speech of the person himself, but that its sense and direction and different relation to the person were due to right temporal lobe activity sending excitation over the anterior commissures and probably the splenium (the back part of the corpus callosum) to the speech areas of the left hemisphere, and ‘heard’ from there.

At the present time, it does not really matter which form of the hypothesis we take. The central feature of both is that the amalgamating of admonitory experience was a right hemisphere function and it was excitation in what corresponds to Wernicke’s area on the right hemisphere that occasioned the voices of the gods.

The evidence to support this hypothesis may be brought together as five observations: (I) that both hemispheres are able to understand language, while normally only the left can speak; (2) that there is some vestigial functioning of the right Wernicke’s area in a way similar to the voices of gods; (3) that the two hemispheres under certain conditions are able to act almost as independent persons, their relationship corresponding to that of the man-god relationship of bicameral times; (4) that contemporary differences between the hemispheres in cognitive functions at least echo such differences of function between man and god as seen in the literature of bicameral man; and (5) that the brain is more capable of being organized by the environment than we have hitherto supposed, and therefore could have undergone such a change as from bicameral to conscious man mostly on the basis of learning and culture.

The rest of this chapter will be devoted to these five observations.

1. That Both Hemispheres Understand Language

The gods, I have said with some presumption, were amalgams of admonitory experience, made up of meldings of whatever commands had been given the individual. Thus, while the divine areas would not have to be involved in speech, they would have to be involved in hearing and in understanding language. And this is the case even today. We do in fact understand language with both hemispheres. Stroke patients who have hemorrhages on the left side of the cortex cannot speak, but still can understand.⁴ If sodium amytal is injected into the left carotid artery leading to the left hemisphere (the Wada test), the entire hemisphere is anesthetized, leaving only the right hemisphere working; but the subject still can follow directions.⁵ Tests on commissurotomized patients (which I shall describe more fully in a moment) demonstrate considerable understanding by the right hemisphere.⁶ Named objects can usually be retrieved by the left hand, and verbal commands obeyed by the left hand. Even when the entire left hemisphere, the speech hemisphere, remember, is removed in human patients suffering from glioma, the remaining right hemisphere immediately after the operation seems to understand the surgeon’s questions, though unable to reply.⁷