Corticofugal effects on different neuron types within the cat's brain stem activated by tactile stimulation of the face.

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Abstract
Neurons isolated at 2 levels in the cat''s brainstem, fired by tactile stimulation of the face, were characterized by their cutaneous receptive field characteristics, their axon projection, by the presence or absence of afferent inhibition, by corticofugal excitatory and inhibitory effects and by their anatomical location. Three neuron groups, equally represented at the level of nucleus tractus spinalis oralis and caudalis, respectively, were identified: "lemniscal" cells with an axon projection onto the contralateral posterior thalamus; "interneurons" with presumed short axons; cells within the reticular formation. All cell types displayed afferent inhibition and both corticofugal excitatory and inhibitory effects. The cortical excitatory and inhibitory fields were examined for each neuron type. The observations support the view that a presynaptic inhibitory mechanism subserves corticofugal inhibitory action, within the somatic sensory pathways, but a post-synaptic inhibitory contribution is not excluded.