Gert-Jan C. Lokhorst


G.J.C. Lokhorst. Hemisphere differences before 1800. Behavioral and Brain Sciences, 8 (4): 642, 1985. ISSN 0140-525X.

Harrington's target article is a fine survey of 19th-century ideas on the cerebral hemispheres, but the history of her subject is longer than she thinks.

In the first place, there is at least one ancient Greek theory of hemispheric specialization. This is how a 12th-century Latin codex describes the views of Diocles of Carystus, a famous Athenian physician from the 4th century B.C.:

He says that phrenitis (madness, frenzy) arises from an inflammation of the heart and an obstruction of the blood or innate heat, from which the brain derives sentience and intellect. The latter is that with which we understand, the former that with which we sense. Accordingly, there are two brains in the head, one which gives us our intellect, and another one which provides sentience. That is to say, the one which is lying on the right side is the one that senses; with the left one, however, we understand. (See Lokhorst 1982a:35)

Diocles's theory is astonishingly modern: the terms he uses, intellectus on the left side and sensus on the right, are even identical to the last entries in Harrington's table. Where the theory comes from is not clear. Before Diocles, Alcmaeon and Empedocles had already distinguished between sentience and intellect; moreover, it may already have been surmised in his time that the hemispheres are different in that each one only controls the opposite half of the body. There is, however, no evidence of an earlier combination of these two ideas. How the theory fared after Diocles's times is clearer: It fell into complete oblivion, the reason for this probably being the emphasis on the unitary system of the cerebral ventricles in later accounts of brain function. Nevertheless, if the early 19th-century brain scientists had shown a greater regard for history, they easily could have known about Diocles's theory: There are no less than three 16th-century editions of the codex (Horatianus 1532; cf. Lokhorst 1982b).

In the second place, there is more to be found in the 18th-century literature than Harrington suggests. I am thinking not only of the discussions about the function of the corpus callosum and the crude split-brain experiments from this period (see Neuburger 1897), but especially of Meinard Simon Du Pui, whose De homine dextro et sinistro (1780) clearly anticipates some of Henry Holland's and Wigan's ideas. Thus, he wrote that man is from a medical point of view a "homo duplex, a right man and a left one" (p. 108); "man's nervous system is just as bipartite as the rest of his body, with the result that one half of it may become affected while the other half continues to carry out its proper functions" (pp. 184-85). Broca knew of these views but considered them too extreme: "The thought is far from me to divide man into two distinct beings, like Du Pui has done" (Broca 1865:393).

Harrington's 19th-century material gives a good picture of the period. However, one should not underestimate the anatomical knowledge available by the end of the century concerning hemispheric differences. For example, the recently discovered fact that the right hemisphere contains relatively more, white matter (i.e., fibers) than the left one (Gur, Packer, Hungerbuhler, Reivich, Obrist, Amarnek & Sackeim 1980) was already known to Van Biervliet (1899, p. 296). Furthermore, mention should be made of a highly curious book, Le duplicisme humain (1906), in which Camille Sabatier, a retired French politician, puts all previous research into one grand, unified perspective.

Finally, what about the use of history for present-day research? I agree that the older literature may yet have a stimulating role to play. However, I fail to see any broader significance of historical investigation for contemporary research. For, suppose a scientist has learned from history how to recognize a time-bound and socioculturally colored theory when he sees one (as Harrington exhorts him to do). Does this help him in his capacity as scientist? No; for no matter how clearly a theory may reflect its cultural or psychological origins, it can still turn out to be either true or false.

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