Elucidating the role of right dorsolateral prefrontal cortex in cognitive-motor interference: Polarity-specific effects of transcranial direct current stimulation.

Cognitive-motor dual-task interference (DTi), characterized by performance deterioration during simultaneous cognitive and motor task execution, presents a critical challenge to daily functioning and increases the risk of falls and accidents, particularly in vulnerable populations. Although increased right dorsolateral prefrontal cortex (DLPFC) activation has been implicated in DTi, the precise functional significance of this activation, including whether it reflects adaptive or task-related processes, remains unclear. This double-blind, randomized, sham-controlled trial demonstrates polarity-dependent behavioral effects of transcranial direct current stimulation (tDCS) applied to the right DLPFC on cognitive-motor dual-task (CMDT) performance in healthy young adults. Seventy-four participants performed a high-load CMDT, which combined a spiral-drawing task using the non-dominant hand with an auditory working memory task (Paced Auditory Serial Addition Test) under anodal, cathodal, or sham tDCS applied to the right DLPFC. Cathodal stimulation significantly impaired motor performance as indicated by reduced drawing speed, whereas anodal stimulation showed a significant trend toward improvement. No significant effects were observed in drawing accuracy or cognitive task performance. Notably, participants with lower baseline motor performance exhibited greater susceptibility to DLPFC modulation, suggesting baseline-dependent differences in behavioral responsiveness to stimulation under cognitive load. These findings indicate that stimulation of the right DLPFC can modulate CMDT performance at the behavioral level and suggest that the right DLPFC may represent a potential target for neuromodulation strategies aimed at enhancing cognitive-motor performance, particularly in populations with reduced executive resources, such as older adults and individuals with neurological or psychiatric disorders.