Gert-Jan C. Lokhorst


G.J.C. Lokhorst. The first theory about hemispheric specialization. Second meeting of the International Society for the History of the NeuroSciences (ISHN) combined with the Sixth meeting of the European Club for the History of Neurology (ECHN), Leiden, June 20, 1997.

The first theory about hemispheric specialization is to be found in a codex from about 1100 A. D. The relevant passage reads as follows (see Figs. 1 and 2):

There are two brains in the head, one which gives us our intellect and another one which provides the faculty of perception. The brain on the right side is the one with which we perceive, whereas the left brain is the one with which we understand.

The text probably dates from late classical antiquity. Its author is not known. The creator of the theory is not known either. He or she may have been inspired by theories about the psychophysiological superiority of the left cardiac ventricle. Some examples of such theories:

The medieval codex was first printed in 1532. The relevant page in that edition is shown in Fig. 3.

ILLUSTRATION: page from codex

Fig. 1. Hemispheric specialization A.D. 1100

ILLUSTRATION: Siq itaque duo cerebra ...

Fig. 2. Enlarged version of a part of Fig. 1.

ILLUSTRATION: Von Neuenar 1532

Fig. 3. Hemispheric specialization A.D. 1532


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