Temporal synchronization for in-phase and antiphase movements during bilateral finger- and foot-tapping tasks

Appropriate motor performance, which must be precisely processed and timed to temporal and spatial requirements, can be studied using a synchronized tapping task. For gait rehabilitation, estimation of bilateral foot-tapping accuracy is important, as walking involves bilateral movements, usually antiphase, of the lower extremities. Rhythmic control of lower limb movements, such as gait, involves voluntary control and may also be automatically regulated by the central pattern generator. This study investigated the temporal synchronization of in-phase and antiphase movements using synchronized bilateral finger and foot-tapping tasks. Thirty healthy young adult volunteers were enrolled and instructed to tap the finger or foot button synchronously with the tones presented at fixed inter-stimulus intervals (ISIs). One of 10 different ISIs (250-4800 ms) was selected for each block, in which 110 tones were presented. Taps were performed by either unilateral or bilateral fingers or feet, either in-phase (to move bilateral fingers or ankles simultaneously) or antiphase (to move bilateral fingers or ankles alternately). The synchronization error (SE) and coefficient of variation (CV) of the inter-tap interval (ITI) were evaluated. In all trials with short ISIs, SEs were narrowly distributed, either clustered around 0 ms or with a slightly negative value. Although SE variability gradually increased with increasing ISI, the CV of ITI was significantly lower for antiphase movement than for unilateral or in-phase movement in the foot-tapping task, but not in the finger-tapping task. The preserved temporal synchronization for antiphase movement of the foot, but not finger tapping, may be due to the neural mechanisms underlying locomotion.