Effects of neck flexion on discriminative and cognitive processing in anticipatory postural control during bilateral arm movement.

We investigated the effect of neck flexion on discriminative and cognitive processing in postural control during bilateral arm movement while standing, using event-related potential (ERP) and electromyogram. Fourteen healthy subjects flexed their arms to the target stimuli with a 20% probability in neck resting and flexion positions. Amplitude and latency of N2 and P3, anterior deltoid (AD) reaction time, onset time of postural muscles with respect to AD activation, and peak amplitude and latency of all muscles were measured. With neck flexion, N2 and P3 amplitudes increased, N2 and P3 latencies and AD reaction time shortened, and onset times of all postural muscles became earlier. No significant differences in peak amplitude and latency of each muscle were found between neck positions. Significant positive correlations were found in changes with neck flexion between P3 latency and AD reaction time, and between N2 latency and onset time of erector spinae. These suggest that with neck flexion, attention allocation to discriminative and cognitive processing increased, and the processing speed increased with shortening of reaction time in focal muscles. In addition, the onset time of postural muscles became earlier without changing the activation pattern, which was associated with the hastened discriminative processing.