Facilitation of transmission in Ib pathways by cutaneous afferents from the contralateral foot sole in man.

Changes in the quadriceps H-reflex were used to study the effect of a weak contralateral cutaneous stimulation upon transmission in Ib pathways from ankle muscles to quadriceps in man. Provided it was applied to the contralateral foot sole, such a stimulation facilitated transmission in Ib pathways to quadriceps (inhibitory from extensors as well as excitatory from flexors). The central latency of this contralateral cutaneous facilitation was 1 msec longer than that of the ipsilateral cutaneous depression of Ib pathways. These findings are discussed with regard to the requirements of bipedal gait.