The present study examined whether the left posterior parietal cortex contributes to the selection process for the initial swing leg in gait initiation. Healthy humans initiated the gait in response to an auditory start cue. Transcranial magnetic stimulation (TMS) was given over P3, P4, F3 or F4 simultaneously, with the auditory start cue, in the on-TMS condition. A coil was placed over one of the four TMS sites, but TMS was not given in the off-TMS condition. The probability of right leg selection in the on-TMS condition was significantly lower than in the off-TMS condition when the coil was placed over P3, indicating that the left posterior parietal cortex contributes to the selection process of the initial swing leg of gait initiation. The latency of the anticipatory postural adjustment for gait initiation with the left leg was shortened by TMS over F4 or P4, but with the right leg was shortened by TMS over P3 or P4. Thus, the cortical process affecting the time taken to execute the motor process of gait initiation with the right leg may be related to the selection process of the initial swing leg of gait initiation.
Keywords: decision making; gait initiation; initial swing leg; posterior parietal cortex; selection.