LAUSR

Light touch reduces sway during standing. Unexpected displacement of a light touch reference at the finger can produce rapid responses in ankle muscles when standing, suggesting cutaneous receptors in the hand are functionally coupled with ankle muscles. Using microneurography in the median nerve, we tested the hypotheses: 1) that cutaneous afferent activity of mechanoreceptors of the hand would modulate electromyographic (EMG) activity of ankle muscles, and 2) that displacement of a light touch contact across a receptor's sensory territory would be encoded in the afferent activity. Spike-triggered averaging of EMG activity of tibialis anterior (TA) and soleus (SOL) demonstrated thirty-four of forty-two (81%) cutaneous afferents recorded modulated activity of ankle muscles with latencies between 40 to 119 ms. Cutaneous afferents of all types (slow and fast adapting, types I and II) demonstrated responses in TA and SOL, in both the ipsilateral and contralateral leg. Activity from eleven cutaneous afferents were recorded while a light touch contact was displaced across their receptive fields. Afferent activity increased with stimulus onset and remained elevated for the stimulus duration for all afferents recorded. These results suggest cutaneous afferents from the hand consistently form connections with motor pools of the leg at latencies implicating spinal pathways. In addition, the same population of afferents is readily excited by the displacement of a light touch contact. Therefore, cutaneous receptors of the hand can be recruited and utilized to alter motoneuron pool excitability in muscles important to balance control, at latencies relevant for rapid balance responses.