Cognitive load alters cortical dynamics during gait in Parkinson’s disease but not in neurologically healthy individuals

The level of difficulty of a secondary cognitive task (DT) can affect gait and cortical activity distinctly in individuals with Parkinson's disease (PD). During a simpler ST, individuals with PD may use a compensatory neural mechanism by reallocating neural resources to preserve gait performance; for difficult DT, this compensation may not be the case. However, whether different levels of difficulty of a single-domain DT would distinctively affect gait and cortical activity in individuals with PD compared to neurologically healthy individuals is still unknown. Fourteen individuals with PD and 14 healthy individuals performed walking trials at self-selected speed, under six conditions of walking with an auditory DT and varying levels of difficulty (very easy: VE-SCT, easy: E-SCT, moderate: M-SCT, difficult: D-SCT, and very difficult: VD-SCT). Gait kinematics and cortical activity data were recorded. RM-ANOVAs identified that individuals with PD showed higher DT cost for both step length and step velocity when the cognitive task was D-SCT or VD-SCT, compared to easier tasks (<i>p</i> < 0.005). Cortical activity showed a different pattern. During more difficult tasks (M-SCT, D-SCT, VD-SCT), PD individuals had a lower DT cost in delta frequency (frontal and motor areas) and beta frequency (parietal area) compared to the easier tasks (VE-SCT, E-SCT) (<i>p</i> < 0.005). These findings suggest that individuals with PD exhibit a distinct pattern of cognitive-motor interaction during dual-task walking, characterized by increased cortical dual-task cost in lower vs. greater gait deterioration in higher task demands. These findings suggest that individuals with PD over-engage cognitive resources while walking with relatively easier DT.