New evidence on the callosal system.

Abstract

In the present paper experimental data on the principles of functional organization of the animal callosal system and the roles of symmetry and asymmetry in interhemispheric interaction are considered. A conclusion has been made that the cerebral hemispheres function not according to homotopicity principle but according to the principle of heterotopicity. A utilization of both homotopical callosal projections and intracortical pathways takes place. In interhemispheric relations the major role is played by the principle of the common pathway. Of great importance in asymmetry organization is the physiological dominant, which is formed and reinforced by excitation spreading through the corpus callosum and along intracortical pathways. Transcallosal excitation, interacting with thalamocortical and extracallosal ones, contributes to the creation and modulation of functional interhemispheric asymmetry.