Neuromuscular control mechanism during posture-cognition dual task in mild cognitive impairment: a concurrent fNIRS-sEMG-COP study

Mild cognitive impairment (MCI) is characterized by cognitive decline. Previous evidence showed that MCI patients showed impairments of postural control, which may increase fall risk, particularly under conditions of concurrent cognitive demand. However, the impact of working memory loads on neuromuscular control of MCI patients during postural task and its underlying neural mechanisms remains unclear. We aimed to investigate the effect of working memory load on neuromuscular control performance and its central mechanisms in patients with MCI. Twenty-two patients with MCI and twenty-four healthy controls (HCs) performed a posture-cognition dual task by rapidly raising the right arm in response to directional cues in an N-back paradigm, with arrows presented randomly upward, leftward, or rightward. Surface electromyography (sEMG) was used to measure the root mean square (RMS) and co-contraction index (CCI) of bilateral trunk and ankle muscles. At the same time, a Nintendo Wii Balance Board was used to record the center of pressure (COP) during posture-cognition dual task, while functional near-infrared spectroscopy (fNIRS) assessed cortical activity. Patients with MCI exhibited significantly lower accuracy in the 2-back task than did HCs, but not in the 0-back or 1-back tasks. The MCI group showed significantly higher RMS values in bilateral ankle muscles and greater postural sway, particularly under higher working memory load. Meanwhile, they also demonstrated increased CCI regardless of the level of working memory load. fNIRS analysis revealed greater activation in the bilateral dorsolateral prefrontal cortex (DLPFC), supplementary motor area (SMA), and primary motor cortex (M1) in the MCI group, along with reduced DLPFC lateralization. Moreover, cortical activation was positively correlated with ankle muscle RMS. These findings suggest that patients with MCI show brain hyperactivation and altered neuromuscular control strategies, which may reflect compensatory mechanisms to maintain standing stability during cognitively demanding postural tasks.