Second somatosensory cortical area in macaque monkeys: 2. Neuronal responses to punctate vibrotactile stimulation of glabrous skin on the hand.

Single neuron responses from the second somatosensory cortical area (SII) of macaque monkeys were studied using computer-controlled vibratory stimuli ranging in frequency from 10 to 300 Hz. Results were obtained using chronic recording techniques in awake or lightly tranquilized animals. Most neurons were unable to follow the temporal order of vibrations in excess of 10 Hz. A smaller sample of cells provided faithful reproduction of frequencies up to 50-75 Hz and another responded to low amplitude, high frequency stimulation in excess of 100 Hz. Cells that displayed temporally cohesive responses to lower frequencies demonstrated predictable, time-locked discharges to successive stimulus cycles. Cells activated by higher frequencies showed a lower probability of following successive stimulus cycles. These findings are discussed in reference to the hypothesis that SII may provide a parallel channel for processing high frequency vibrotactile inputs from Pacinian receptors.