The corpus callosum, interhemisphere interactions, and the function of the right hemisphere of the brain

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

Cognitive functions in patients with stenotic lesions of the great arteries of the head before and after carotid endartectomy

Objective: to study higher mental functions (HMF) in patients with stenotic lesion of the brachiocephalic arteries (BCA) before and after carotid endarterectomy (CE). Patients and methods. Prior to and following CE, 97 patients underwent neurological examination, neuropsychological syndrome analysis described by A.R. Luria, evaluation using the Wexler verbal working memory scale, Stroop word-digital test, and Schulte test. BCA ultrasound duplex scanning and cerebral perfusion were made over time. Results. Preoperative neuropsychological study revealed abnormalities in 98% of the patients. There was most common bilateral frontal dysfunction and deep structural pathology, which were more pronounced in persons above 50 years of age and in the presence of mixed BCA stenosis. Stenosis-associated unilateral parietal and temporal dysfunctions were more frequently registered. Within 30 days after CE, the maximum HMF changes were found in patients having unilateral stenosis. There was ameliorated dysfunction of the structures blood is supplied to which by an operated vessel and the vertebrobasilar system. Poststroke patients were found to have a significant intraoperative HMF reduction in the early rehabilitation period of stroke. The syndromes having common and local mechanisms of development and different topic sites were identified among the short-term and reversible HMF impairments. Conclusion. Despite heterodirectional HMF changes in the early period after BCA reconstructive operations, the positive cognitive functional changes in all the patients at 30 days of CE confirm the rationale for and efficiency of surgical intervention

Understanding the mechanisms of callosal development through the use of transgenic mouse models

The cerebral cortex is the area of the brain where higher-order cognitive processing occurs. The 2 hemispheres of the cerebral cortex communicate through one of the largest fiber tracts in the brain, the corpus callosum. Malformation of the corpus callosum in human beings occurs in 1 in 4000 live births, and those afflicted experience an extensive range of neurologic disorders, from relatively mild to severe cognitive deficits. Understanding the molecular and cellular processes involved in these disorders would therefore assist in the development of prognostic tools and therapies. During the past 3 decades, mouse models have been used extensively to determine which molecules play a role in the complex regulation of corpus callosum development. This review provides an update on these studies, as well as highlights the value of using mouse models with the goal of developing therapies for human acallosal syndromes