Ontogenesis of transcallosal responses in cats: I. Formation of interhemispheric connections in kittens in the first month of life.

In acute experiments on kittens at the age of 1 to 30 days, anaesthesized with nembutal and immobilized with diplacine, multiple transcallosal response (TCR) recording from different cortical areas was performed. In 2-15-day kittens homotopical TCRs appeared earlier, were wider represented, and revealed a greater configuration maturity and amplitude-time parameters in associative (parietal and sensorimotor) areas as compared to projection (somatosensory, visual and auditory) zones. It has been established that interhemispheric relations in the kitten associative cortex are mediated, not only by the callosal, but also by the extracallosal system, which was evidenced by the presence of late negative components preserved after callosotomy. The results of per-layer analysis of interhemispheric responses in 1 month kittens have shown that in the parietal cortex, in the course of development, the drains of surface-positive oscillation shifted from the V to the III layer, whereas the drain of surface-negative deviation remained at the level of II-III layers. The late component was registered at the depth of layers III-IV, having a drain in the I-II layers. In the sensorimotor cortex, the surface-negative oscillation had a drain in the I-II layers, whereas the surface-positive oscillation had a drain in the II and V-VI layers. The data obtained reflect the dynamics of the formation of interhemispheric relations in the first-month-of-life kittens and testify to an increased level of their integrative interaction.