Comparison of sensory discrimination thresholds with muscle and cutaneous nerve volleys in the cat.

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Abstract
Animals were trained to bar-press in response to sensory cues resulting from direct stimulation of peripheral nerves. With cutaneous nerve volleys, sensory discrimination thresholds occurred at stimulus intensities which produced a threshold response in the peripheral nerve and in the cerebral cortex. In the same subjects, Group I afferent volleys from f orellmb and hindlimb muscle nerves did not evoke a discriminative response. Sensory discrimination threshold with deep radial nerve volleys occurred near Group II threshold (1.7 T). Discrimination with hamstring nerve volleys did not occur until stimulus intensities approached Group HI threshold (about 3.5 T). Group I volleys from the deep radial nerve evoked large amplitude responses in a small region of the posterior slgmoid gyrus in the awake cat; however, in spite of the presence of the evoked response the subjects failed to discriminate Group I afferent volleys. The experiments revealed that an evoked response in the cerebral cortex is not necessarily associated with discrimination and provided direct evidence that stretch receptor afferents from striated skeletal muscle do not subserve kinesthesis.