Slowly adapting type I mechanoreceptor discharge as a function of dynamic force versus dynamic displacement of glabrous skin of raccoon and squirrel monkey hand

The effects of dynamic force and dynamic displacement on single unit discharge rate during ramp stimulation were examined in 10 raccoon and 8 squirrel monkey slowly adapting Type I (SAI) mechanoreceptive afferent fibers, all having receptive fields on glabrous skin of the hand. In all 18 cases, power function exponents were higher for effects of dynamic displacement than for effects of dynamic force on discharge frequency. Thus, these SAI mechanoreceptors are more sensitive to variations in dynamic displacement than to variations in dynamic force. This differential sensitivity may be explained by the fact that the relationship between dynamic force and dynamic displacement is, itself, nonlinear, dynamic displacement being a power function of dynamic force, with exponents less than 1.0.