fMRI analysis of active, passive and electrically stimulated ankle dorsiflexion

Ankle dorsiflexion (ADF) is an integral component in gait. The objective of this study was to define, using functional magnetic resonance imaging (fMRI) in healthy volunteers (n=12), the brain regions that are activated during Electrical Stimulation (ES)-induced ADF movements, and compare this to the pattern of activation occurring during active and passive ADF. Concurrent electromyography (EMG) was used to monitor the tibialis anterior muscle activity so as to allow EMG-guided fMRI analysis to be performed. Patterns of cortical and sub-cortical activation in response to active, passive and ES-induced ADF movement were identified. EMG-guided fMRI analysis was shown to improve detection and reduce inter-session variance for active and ES tasks. A significantly greater number of voxels were activated during active and ES-induced ADF compared to passive ADF in contralateral primary motor (M1), primary sensory (SI), and secondary somatosensory (SII) areas, as well as in supplementary motor area (SMA) and cingulate motor areas (CMA); bilateral dorsal and ventral premotor areas and cerebellum VI. The contrast of active greater than ES-induced ADF showed increased activation in SMA, contralateral PMdr; bilateral PMvr, dorsolateral prefrontal cortex and CMA; and ipsilateral cerebellum IV. Active ADF generated greater activation in brain areas responsible for motor planning, execution and visuomotor co-ordination. ES-induced activation was greater in bilateral SII and insula than for active ADF, hypothesised to result from increased sensory integration, but also possibly due to a nociceptive component to ES.