Studies on the efferences from the nucleus medialis of the thalamus to the cortex and strio-pallidal structures in cats

Abstract

1. Evoked potentials were recorded in cats to study the distribution of axons leaving the Centrum Medianum of thalamus (CM). 2. Non-repetitive CM stimulation elicits surface-positive potentials onto the associative cortex: anterior sigmoid gyrus, anterior marginal gyrus and suprasylvian gyrus (minimal latencies, 2, 4, 6 ms). The stimulation of these cortical foci by electrodes in the grey matter does not evoke in the CM any asynaptic response. It is concluded that the cortical response is not a sufficient indication of a cortical projection of the CM. 3. Associative cortical responses evoked by somatic stimulation are not affected either by electrocoagulation of CM or by cooling the CM with a cryogenic probe insulated except at the tip. Hence the CM does not seem to contribute to relay somatic activation from the periphery to the ipsilateral cortex. 4. Asynaptic responses (0.2–0.8 ms latency) and corresponding postsynaptic responses (0.5–1.5 ms latency) are recorded in the internal capsule, dorsal parts of putamen and globus pallidus, and in the entopedoncular nucleus. 5. Long latency waves are also recorded in these regions, in the amygdaloid complex (2–9 ms latency) and in the caudate nucleus (minimal latency, 12 ms). Their distribution and their latencies are not related to those of the asynaptic responses. 6. The hypothesis that the CM plays a role in pain is discussed on the basis of hodological data.