The sense of flutter-vibration evoked by stimulation of the hairy skin of primates: Comparison of human sensory capacity with the responses of mechanoreceptive afferents innervating the hairy skin of monkeys

SummaryWe have studied the response properties of peripheral myelinated fibers ending in the hairy skin of the Rhesus monkey, activated by sinusoidal mechanical stimulation. In parallel experiments we measured thresholds of the sensations evoked in man by identical stimuli, delivered under similar conditions to corresponding areas of the hairy skin. We found that the sense of low frequency vibration (i. e., flutter) depends upon activity in rapidly adapting alpha fibers which end in or about the hair follicles. High frequency vibration is signalled by Pacinian afferents whose terminals lie deep to the skin itself. These two sets of fibers, by reason of their discharge patterns and differential sensitivities in different frequency ranges, are thought to provide the essential first order input for the human sense of vibration evoked by stimulation of the hairy skin. Rapidly adapting cutaneous afferents of the delta size and two classes of slowly adapting alpha fibers are also entrained by mechanical sinusoids, but are thought not to contribute to vibratory sensibility. Our findings support the proposition that the sensitivity of humans to oscillatory mechanical stimuli at different frequencies, and the quality of the sensations evoked by them, are determined in the first instance by the properties of two distinct sets of peripheral afferent fibers.