Changes in muscle and cutaneous cerebral potentials during standing.

The cerebral potentials produced by electrical stimulation of mechanoreceptive afferents from the foot were recorded in the sitting and standing postures to determine whether transmission to cortex was altered by the postural change. The latencies of the early components of the cerebral potentials produced by muscle afferents (posterior tibial nerve) and cutaneous afferents (sural nerve) did not change with posture. Standing was associated with an approximately 25-35% decline in amplitude of the earliest components of the posterior tibial cerebral potential (N38-P40, P40-N50) for a stimulus intensity associated with a submaximal afferent volley. The amplitude of the equivalent N38-P40 and P40-N50 components produced by sural afferents also declined during quiet stance. In most experiments the subcortical component (P32-N38) was not reduced by stance so that the amplitude attenuation probably occurs in part at cortical level. Qualitatively similar changes in the cerebral potentials were documented for a range of stimulus intensities, including those which evoked a maximal initial component in the nerve volley. For a similar reduction in the initial (N38-P40) component of the cerebral potential, voluntary plantar flexion in the sitting position produced less attenuation in subsequent components than did standing. Thus, attenuation of the cerebral potential during standing may involve specific posture-related factors in addition to those related to volition.