Cortical representation of whole-body movement is modulated by proprioceptive discharge in humans

Previous studies have revealed the influence of ongoing sensory discharge on modulating the central representation of muscle afferents from individual limbs. In the present study, we explored the potential for such modulatory influence on the afferent discharge arising from induced whole-body movement. Vestibular and somato-sensory inputs arise from such whole-body movement. The convergence of these two modalities is important in motor control, especially for the maintenance of postural stability. We hypothesised that transmission of proprioceptive and vestibular information to the cortex would be reduced as a result of muscle-spindle discharge in knee extensor muscles. Perturbation-evoked responses (PERs), recorded from central scalp electrodes (C3, CZ, C4), were evoked through rapid translations of subjects who were seated in a chair on a movable platform. PERs were recorded during passive linear translations alone and preceded by vibration of the patellar tendon. The PER was characterised by a slow, negative potential peaking at approximately 150 ms (N150) following displacement of the chair. The amplitude of the PER was reduced following vibration to 56% of the control. Such reduction of PERs was comparable to the attenuation of somatosensory evoked potentials and soleus H-reflex magnitudes from tibial-nerve stimulation. We conclude that muscle-spindle discharge in knee extensor muscles leads to gating of both of these afferent pathways. These results have potential implications to the understanding of the CNS control of stability during ongoing movement.