Changes in event-related potentials associated with postural adaptation during floor oscillation.

The event-related potential (ERP) mainly reflecting activation of the frontal lobe was measured during periodic floor oscillation, and changes in postural preparation and attention to the postural disturbance according to this adaptation were investigated. The experiment consisted of two tasks with eyes closed: adaptation to floor oscillation and finger flexion coinciding with the anterior and posterior reversals of oscillation. Subjects were 20 healthy young adults. They maintained a standing posture for 1 min (1 trial) on the force platform which oscillated in the anteroposterior direction at 0.5 Hz and an amplitude of 2.5 cm. ERP from a Cz electrode, activity of postural muscles and the center of foot pressure in the anteroposterior direction (CoPy) were analyzed. In the adaptation task, the speeds of CoPy fluctuation gradually decreased and reached a plateau between 4th and 14th trials, with inter-subject differences. Posterior postural muscles were activated in response to the anterior reversal of oscillation according to adaptation and also in the finger flexion task, with the largest activation of the gastrocnemius (GcM). A negative ERP peak was observed to occur locally around the anterior reversal of oscillation after adaptation. The peak ERP time had the strongest positive correlation with the peak activation time of the GcM, and the amplitude of the negative peak decreased with adaptation. In the finger flexion task, a negative ERP peak was observed around each target point. This negative peak was related to the anticipatory attention directed to the reversal point and to motor preparation for finger flexion. It is conceivable that the increasing negative ERP in the adaptation task reflects the dynamics of motor preparation and attention mainly for the anterior reversal, where the negative ERP peak is closely related to anticipatory information processing of somatosensory stimuli arising around the time of the reversal.