Cell sparse zones in the ventrolateral thalamic mass in humans, monkeys and cats: their special reference to kinesthetic neurons

The Vim nucleus of the human thalamus is the cell sparse zone. The neurons in this zone respond to peripheral stimuli of kinesthetic modality with a short latency. In the cytometrical study, the cell sparse zone is identifiable in both the monkey and cat thalamus. The cell dimension and density in a 1 mm2 area in the cell sparse zone of each species are as follows: humans--large neuron 500-900 microns2, medium neuron 200-400 microns2, cell density 60-90/mm2/50 microns thickness; monkeys--large neuron 400-800 microns2, medium neuron 200-400 microns2, cell density 120-250/mm2/50 microns thickness; cats--large neuron 400-800 microns2, medium neuron 200-400 microns2, cell density 120-250/mm2/50 microns thickness. In this zone, there are large and medium thalamocortical relay neurons defined by the Golgi impregnated and HRP studies. It is still obscure which neurons respond to kinesthetic stimulation and which neurons or afferent fibers play important roles in the tremor mechanism.