[Interhemispheric transfer and its implications for neurology and psychiatry].

The corpus callosum (CC) is the brain's most important connection between cortical areas of both hemispheres. Due to the hemispheric lateralisation of brain function, information transfer between both hemispheres is vital for an optimal performance in tasks, in which several psycho-motor functions have to be integrated. Dysfunction of the CC can lead to deficits in neuropsychological tasks and could contribute to pathologies underlying psychiatric illnesses. In this review the normal and abnormal development of the CC as well as its macro- and microscopic anatomy will be outlined. Then the detrimental effects of operative callosomy on different modalities, e. g. on vision, the somatosensory and the auditory system, will be discussed. Two electrophysiological methods will be introduced, with which interhemispheric communication can be studied: hemispheric transfer in rapid visuo-motoric tasks (CUD) and transcallosal inhibition (TI), a phenomenon which occurs in a special paradigm of transcranial magnetic stimulation. A first study found TI to be reduced in unmedicated schizophrenic patients. This suggests that an inhibition between motor cortices could be reduced in schizophrenic patients. Further results of other studies, which have analysed the CC and interhemispheric transfer in schizophrenic patients, will be introduced and discussed. In future experiments, the contribution of dysfunctions of transcallosal transfer to psychopathological symptoms and neuropsychological deficits in schizophrenia should be studied.