Working memory load modulates sensorimotor cortical oscillations underlying anticipatory postural adjustments during...

During step initiation, the body first shifts toward the swing leg and subsequently toward the stance leg. The initial shift toward the swing leg, termed anticipatory postural adjustments (APAs), enables smooth transfer of body weight to the stance leg. Working memory (WM) load has been shown to increase erroneous APAs under visual interference; however, the underlying neural mechanisms remain unclear. The purpose of this study was to investigate cortical activity associated with WM load-induced increases in erroneous APAs during step initiation. Sixteen healthy young men performed a stepping task under two WM load conditions (LOW and HIGH). Participants initiated a volitional step in response to visual stimuli under congruent and incongruent (INC) conditions based on a Flanker task, while memorizing either one digit (LOW WM load) or six digits (HIGH WM load). Cortical oscillatory activity during step initiation was recorded using electroencephalography. The results showed that, in the INC condition, the APA error rates were significantly greater under HIGH than LOW WM load and that theta-band synchronization in the sensorimotor area was enhanced under HIGH compared to LOW WM load. These findings suggest that increased WM load requires greater recruitment of the sensorimotor area to meet heightened cognitive demands during step initiation. Inefficient engagement of this area may lead to inappropriate weight shifting, thereby resulting in APA errors.