The corpus callosum is the largest commissure of the brain. Callosal fibers have been shown to connect homotypic (symmetrical) areas of the cortex in the two hemispheres; fibers in the splenium of the corpus callosum run to the occipital areas, and fibers in the body of the corpus callosum run to the temporal and parietal lobes; interhemisphere fibers of the frontal parts of the neocortex, located in the rostral parts, form the genu and rostrum of the corpus callosum Syndromes resulting from lesions to the corpus callosum in humans and animals were not identified for a long period of time. Sperry Basic data on the functions of the corpus callosum were obtained from studies of patients undergoing transection of this structure for the treatment of incurable epilepsy. The theoretical basis for this operation was the suggestion that transection of the corpus callosum would prevent interhemisphere propagation of epileptic discharges. The first sagittal transections of the corpus callosum were performed in 1940 by Van Eagenen and Herren [30] in 24 patients. Detailed psychological studies of these patients were not undertaken, though impairment of coordination of movements of the left and right hands was noted. Isolated commissurotomy was later found to be clinically ineffective, and deeper splitting of the brain came into use for the treatment of epilepsy, i.e., transection of the corpus callosum was supplemented with transection of the Neuroscience and Behavioral Physiology, Vol. 35, No. 5, 2005 The 473 Translated from Zhurnal Nevrologii i Psikhiatrii imeni S. S. Korsakova, Vol. 104, No. 5, pp. 8-14, May, 2004. Original article submitted December 2, 2003 A complex clinical-neuropsychological study was performed by the Luriya method before and after surgery in 36 patients with arteriovenous malformations (AVM) of the corpus callosum. The symptoms of local lesions to the various parts of the corpus callosum are described. Symptoms of partial lesioning of the corpus callosum were found to be modality-specific, though only relatively. The symptoms of dyscopia or dysgraphia could appear in isolation fro each other. Combined lesions of the medial parts of the brain (cingulate cortex, frontal lobes) and the corpus callosum significantly increased the level of dysfunction of these medial parts. Patients with lesions to the anterior parts of the corpus callosum showed symptoms of frontal lobe dysfunction. Lesions to the corpus callosum led to dysfunction of the right hemisphere in the spheres of emotion, perception, and spatial activity. Previous studies have demonstrated that the right hemisphere integrates impulses from both sides of the space and is the first zone involved in activity, performing its initial stages. The author believes that this synthetic activity of the right hemisphere, with tight connections with the "conscious" left hemisphere, is required for the formation of the overall conceptualization of both individual objects and particular types of activity. From this point of view, it is the right hemisphere that can, in a sense, be regarded as dominant, rather than the left hemisphere
