THE FIRST THEORY ABOUT HEMISPHERIC SPECIALIZATION

Gert-Jan C. Lokhorst

1997

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 human mind [hê gnômê] is located in the left ventricle and rules over the rest of the soul ("Hippocrates," De corde 10, Littré IX 88).
Diogenes [of Babylon] locates the leading part of the soul in the arterial chamber of the heart, i.e. the pneumatic one ("Galen," De historia philosophica 28, Kühn XIX 315).

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

Fig. 1. Hemispheric specialization A.D. 1100

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

Fig. 3. Hemispheric specialization A.D. 1532

Literature

For more information, see

G. J. C. Lokhorst. The first theory about hemispheric specialization: Fresh light on an old codex. Journal of the History of Medicine and Allied Sciences 51 (1996) 293-312. hemispheres.pdf
G. J. C. Lokhorst. De oudste theorie over hemisfeerspecialisatie. Gewina 18 (1995) 37-50. gewina95.pdf

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