Neural substrates of cognitive load changes during a motor task in subjects with stroke

A critical component to rehabilitation is the degree to which we challenge patients to facilitate learning without providing excessive competition for cognitive resources. The purpose of this study was to examine brain activation and motor performance during changes in cognitive load in a continuous motor task in subjects with stroke (n = 7) and healthy subjects (n = 17).

Subjects participated in a joystick drawing task during functional magnetic resonance imaging. Subjects attempted to continuously draw a square under three conditions of varying cognitive demands.

In subjects with stroke, results showed significantly less activation in contralateral primary motor area when the task did not require working memory demands and no change when the condition required online visual feedback processing. Bilaterally, the premotor cortex also demonstrated a significant decrease in activation when the task did not require working memory and then an increase in activation when online visual feedback processing was required. Despite these changes in activation, the accuracy of performance was maintained across the three conditions. Healthy subjects demonstrated no significant differences in activation between conditions.

These data suggest that the sensorimotor areas investigated have the greatest demand when the task requires working memory, but that only the bilateral premotor area has increased demands when online visual feedback processing is required. Use of working memory and visual feedback should be carefully considered when designing rehabilitation programs to balance challenging patients with overwhelming their potentially limited cognitive resources.