An electron microscopic study of the termination of thalamocortical fibres in areas 3b, 1 and 2 of the somatic sensory cortex in the monkey.

The degeneration of the terminals of thalamocortical fibres has been studied in areas 2b, 1 and 2 of the first somatic sensory area of the monkey 4 and 5 days after large electrolytic lesions in the ventral posterior nucleus of the thalamus. The number of degenerating terminals is much greater and the rate of their degeneration faster in area 3b than in areas 1 and 2, and in all areas they are concentrated in a band occupying the deep part of layer III and the upper half of layer IV. Two examples of dendrodendritic synapses were found in the deep part of the somatic sensory cortex, one in area 3b and the other in area 1.