Cutaneous facilitation of transmission in Ib reflex pathways in the human upper limb.

Group I effects from wrist extensors to flexors, i.e. an early inhibition followed by a relative facilitation which are thought to be Ia and Ib in origin respectively, were compared in control conditions and when preceded by a weak cutaneous stimulation. Stimulating the skin of the dorsal side of fingers II-III, which did not modify the test reflex size when applied alone, increased Ib facilitation. By contrast this Ib effect was not changed by stimulation of the skin of the palmar side. It has previously been shown that heteronymous Ib inhibition in the lower limb during voluntary contraction is facilitated by cutaneous stimulation from restricted receptive fields. Thus, present results lend support to the idea that cutaneous facilitation of transmission in Ib reflex pathways might be functional in curtailing exploratory movements.