Regional differences and interindividual variability in sensitivity to vibration in the glabrous skin of the human hand.

Thresholds for sensation of continuous sinusoidal skin displacements were determined in 7 different test points in the glabrous skin area of the right hand of 11 human subjects. While the subjects were tracking the threshold, the frequency of the sine wave was continuously varied between 0.8 Hz and 400 Hz. THe obtained threshold-frequency functions showed systematic differences between test points at frequencies below 40-60 Hz. These differences were closely related to density in the skin of the afferent mechanoreceptive units most likely accounting for the decisive afferent signals. At higher frequencies, the interregional variation was less marked whereas there was a pronounced variation between subjects. It was proposed that the detection of the type of stimuli used was based on activity in 3 different mechanoreceptive systems.