FIGURE 2.

Representative responses to transcranial magnetic brain stimulation in the tibialis anterior muscle of one 23-year-old female and one 73-year-old male participant while standing on rigid and foam surfaces with eyes open (EO) and eyes closed (EC). Waveforms represent the motor evoked potential averaged over 10 trials in response to an unconditioned test pulse (thing gray line) and to a conditioned test pulse (thick black line) at 2.5 ms interval. Note the absence of modulation of short interval intracortical inhibition (SICI) across the four conditions in the young subject, in contrast to the old subject who decreases SICI when sensory conditions are altered.