Medicine, Mind, and the Double Brain

A Study in Nineteenth-Century Thought

by Anne Harrington

Left Brain and Right Brain in an Immodest Century

She begins (after airing some very general methodological issues in her preface, to which we'll return) by considering the pre-history of hemispheric asymmetry, before c. 1860, starting with Descartes but quickly moving on to the phrenologists under Franz Joseph Gall, who were the first to clearly articulate ideas about the localization of functions in the brain. (She tweaks Gall for having first evolved his system and then starting to examine cases, unlike Darwin, who ``did not first conceive of natural selection, then sail to the Galapagos to confirm his idea.'' Such unreconstructed inductivism is very odd coming from someone of her sympathies, and Darwin himself knew better, though, coming as he did long before Whewell, Bernard and that lot, Gall may not have had a proper methodologist's license for his procedure.) Indeed, her account fills me with respect for the phrenologists, for having grasped the important issues in any genuinely explanatory theory of mind --- ``there must exist an innate material base for the organization of sensations in the mind, just as there was a material base for the process of sensation itself'' (p. 8), and it is not sufficient to dump all this, all the different mental tasks human beings perform, into the lap of a single, undifferentiated entity, whether it be called soul, mind or brain. Lange was mocking the phrenologists when he said that their picture of the mind was like ``a parliament of little men together, of whom, as also happens in real parliaments, each possesses only one single idea which he is ceaselessly trying to assert . . . . Instead of one soul, phrenology gives us nearly forty'' (as quoted on pp. 8--9), but this is in fact one of their merits, and they really ought to be adopted with pride as ancestors by all who hope to naturalize cognition and consciousness. (Dennett could even use the Lange quote as an epigraph.)

But, as I said, the importance of Gall and phrenology for this study lies, first, in their advancing the idea that specific mental functions are localized in specific regions of the cortex, and second, that one hemisphere could be damaged without malfunction, because the other hemisphere had a corresponding functional region which was unhurt. (Phrenology's degeneration into something like the psychoanalysis of its day --- ``its transformation into a social crusade with left-wing, radical tendencies [and] growing association with other suspect ideas such as mesmerism'', while important and amusing, is outside the proper scope of Harrington's book, and is only touched upon.) Both these ideas --- localization of functions, and their duplication in the hemispheres --- were eventually to combine, but the second, gradually transformed into the notion that the two hemispheres could, under propritious (?) circumstances, act and think independently of each other, carries the story up to about 1860. (Localization seemed to be undermined by some pretty experiments by Flourens, who however erred by ``cut[ting] indiscriminately through the brain, disregarding structural variations in the cortex''.) In particular, the idea was abroad that insanity was (at least sometimes) the result of the two hemispheres both becoming independent and functioning minds; this view received its climactic exposition at the hands of the now deservedly forgotten Dr. Arthur Ladbroke Wigan of Brighton, to whom Harrington gives twelve pages.

The second chapter returns to the idea of functional localization, specifically the localization of language, and Broca's discovery of aphasia (or, as he called it, aphemia). This is a pretty complicated story, full of ambiguous evidence, acrimonious debates, shifting theories and arguments, and Harrington does a good job of presenting a confusing situation without simply confusing the reader.

Harrington goes over the general background of the French localization debates, the evidence, including the famous case of Tan, that led Broca to localize the ``faculty of coordinating the movements appropriate for articulate language'' in the part of the frontal cortex now called Broca's Area (helpfully marked on the charts of the brain in the appendix), the debates which began in the Académie de M&ecaute;decine but by no means stopped there, and the eventual, curiously reluctant realization that language was localized in the left hemisphere, that the two halves of the cortex were functionally asymmetric.

One effect of Broca's discoveries was to open the way for Wernicke's exemplary work on aphasia, and the rise of a whole German school of neuropathology (which produced many works of great value, and also Freud). Another, to which Harrington devotes more attention, was unleashing a flood of raw speculation about localization and asymmetry; the guiding principle seems to have been the idea that ``more evolved'' creatures are more asymmetric, and that, the higher the function, the more it is localized in the frontal lobes or in the left hemisphere, or of course in the front left --- like Broca's area. Everyone Harrington mentions found reason to believe that Europeans were more asymmetric than others (with the inevitable differences as to which sort of European came out on top), and men more asymmetric than women. (It is not clear whether she has given us a represnetative sample of this literature.) Then as now, enthusiasts of hemispheric asymmetry thought of the left hemisphere as masculine and the right hemisphere as feminine (though nowadays the valuation attached to this is rather different). The booby-prize for efforts in this direction must surely go to Gaëtan Delaunay, a self-described ``comparative biologist'' whose follies occupy Harrington for three pages:

[H]e seemed to find reason to believe that, in fact, women lacked a good portion of that right-sided/left-brained asymmetry that Broca had taught signified a high level of evolution. His researches, for example, had convinced him that left-handedness was significantly more common among women than men. Even women who were right-handed, he said, tended to have many left-handed habits (e.g., women buttoned their coats left over right, while men did the reverse.)
In a later work, Delaunay went on to suggest that ``the primary cause'' of the link between lateral asymmetries and gender differences was probably embryological. In light of research showing that every embryo was a ``fusion'' of his mother and father, it was not unreasonable to suppose that the ``male element'' always developed into the right side of the body (and apparently the left half of the brain), while the ``female element'' always developed into the left side of the body. Presumably, other forces were at work that caused either the female or the male ``element'' to predominate in the embryo, giving rise to sexual differentiation, though this problem was not addressed. Among the more remarkable pieces of evidence Delaunay cited in support of his argument were two cases apparently reported by Dr. Sibley in the United States. The first of these described a young girl with black hair on the right side of her skull like her father and red hair on the left side of her skull like her mother; the second was concerned with a mulatto child, born of a white father and a black mother, who had smooth hair with fair skin on the right side and kinky hair with dark skin on the left. . . .
Delaunay came to the conclusion that members of the superior groups tended to gravitate towards the right in walking, presumably owing to the controlling influence of their more developed left frontal lobes. Members of inferior groups, on the other hand, tended to direct themselves to the left. Similarly, superior races tended to rotate to the right (``In France, in all our national dances, we turn to the right''); while middling inferior races (the Chinese, Japanese, Turks, Mexicans) turned towards the left; and somehow the most inferior races of all (negroes, for example) managed not to turn at all! Superior individuals also tended to cross their right legs over their left, thus sitting predominantly upon their left buttocks; inferior individuals did the reverse. This last was determined by examining the amount of wear-and-tear on the rear of the individuals' trousers. [pp. 89--91, references omitted]

The fourth and fifth chapters return to the theme of ``duality of mind'', which became increasingly popular in the last third of the century. Harrington notes that this had no real logical connection with the discoveries of Broca and other neurologists, and she waves her hands in the direction of claiming some sort of general, peculiarly nineteenth-century interest in ``self-dividedness and duality'', going so far as to give a laundry-list of nine cannonical authors who wrote on this theme. The best reply to this was given by Lichtenberg: ``You have discovered these traits together ten times, but have you counted the times you have not found them together?'' --- This is however a short burst of folly, from which she quickly recovers, going on to explore the various sorts of mental duality which people invoked hemispheric separation to explain: partial insanity, hypnosis, mediumship, split personality (including the difficulties posed by cases of more than two personæ), spirit-writing, the distinction between subject and object, and so on; and also a curious movement to educate both brains together, rather than just the dominant hemisphere. The work of the German school on apraxia gets squeezed in to the end of chapter five.

Chapter six takes us into another full-blown French academic brawl, about hysteria and its treatment. In one corner, we have Charcot and his school at the Salpêtrière, convinced that hysteria is caused by ``functional'' disorders in the brain (i.e. ones without observable lesions), and that hemilateral hysterias, effecting only one side of the body, were associated with ``a sort of mental dissociation resulting from the apparent independent functioning of the two brain-halves''. Charcot's group even went so far as to claim to hypnotize one side of the brain alone, and produced some striking evidence in the form of hysterical symptoms confined to one half of the body. Alas, they thought that the eyes connect to the contralateral hemispheres, whereas it's really the visual fields which so connect, there being cross-over from each eye. Because of this, their mesmeric gestures (and, of course, words) went to both hemispheres.

21 August 1997