Neurons of the Medial Diencephalon. I. Somatosensory Responses and Caudate Inhibition

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Abstract
Units of the medial diencephalon were studied extracellularly in cats under chloralose anesthesia. An analysis of unit responses to somatic and caudate stimulation indicated that units with a convergent somatosensory input are found in dorsomedian nucleus, centrum medianum and zona incerta. The somatosensory response latencies differ significantly between these 3 regions. Inhibition of somatosensory responses by ipsilateral and contralateral caudate stimulation is predominant in centrum medianum and dorsomedian nucleus but rare in the subthalamus. Excitatory responses to ipsilateral caudate stimulation are observed in about 30% of centromedian and subthalamic neurons but very few dorsomedian units. While the caudate origin of the inhibition appears well established, the excitation may be due to stimulation of corticofugal fibers. Results indicate that inhibition and excitation act upon convergent afferent activity at levels caudal to the diencephalon. The afferent convergence system in the thalamus is differentiated anatomically and functionally in terms of afferent input and central modulation.