Le corps calleux dans la dynamique cérébrale

Summary

It is shown that the physiology of the corpus callosum, the greatest cerebral commissure, has made striking progress in recent years. Electrobiological, neurosurgical, and psychophysiological studies have demonstrated its functioning as an apparatus of immediate transmission of elementary sensory messages and of interhemispheric transfer of organized unilateral learnings. The symptoms which, in animal and in man, follow its complete section are now well known. These symptoms can be described as the manifestations of a disruption of mental unity, contrasting with the maintenance of a surprisingly good behavioural cohesion, and characterized, in conflicting situations, by the shifting dominance of one or the other hemisphere. Furthermore, the dependence of the bilateral synchrony of cortical electrical activity on the callosum has been confirmed by the long-term study of split-brain cats.

In a discussion of the fundamental biological significance of the great cerebral commissure, the author stresses the theoretical importance of the recently demonstrated continuous interhemispheric exchange of callosal impulses, which reflects faithfully the fluctuations of the attention level of the waking brain and disappears completely in deep sleep and in barbiturate narcosis. The experimental data underline the essentially dynamogenic character of this tonic activity, but a more refined analysis may reveal its inhibitory components as well. By analogy with the rostral (rhinencephalic) portion of the anterior commissure which connects the two olfactory bulbs, it is suggested that the original function of corpus callosum may have been the maintenance of a dynamic equilibrium between the two neo-cortices. Its operation as a mechanism of interhemispheric communication and of duplication of memory traces would have been super-imposed on this primitive activity in the course of the phylogenetic evolution of the brain, culminating in the dominance of the right hemisphere in man.