Somatotopic organization of nucleus reticularis thalami in chronic awake cats and monkeys.

Responses of cells in the nucleus reticularis thalami (nRT) to peripheral stimulation were studied in chronic cats and monkeys. The activities were recorded through glass micropipettes. Natural stimulation as well as electric stimulation of implanted nerves were employed in 5 cats and 2 monkeys. In the nRT, 30% of the cells studies in the cat and 60% in the monkey were driven by non-noxious stimulations. A topical organization was demonstrated; however, it is not as precise as that shown for the ventrobasalis (VB) nucleus. The size of peripheral fields was larger than that of cells in the VB nucleus. The modalities of activation of these cells were similar to those of the different specific thalamic nuclei. The mean response latency to peripheral stimulation was longer and the fluctuation in the latency more important than those of the specific thalamic relay. The observations lend support to the hypothesis that most, if not all, of the nRT neurons are innervated by axon collaterals of the thalamocortical or corticothalamic bundles. Burst activities were not numerous in chronic cats (12%) and scarce in monkeys. These bursting neurons are mainly found in the perigeniculate area.