Self-paced and externally triggered rhythmical lower limb movements: a functional MRI study.

Self-paced rhythmical lower limb movement is an important component of locomotive motion in humans. External stimuli are known to facilitate the generation of rhythmical motion. The importance of such self-paced and externally triggered movements is widely recognized, and these movements of the upper limbs have been studied in detail. However, the difference in neural mechanisms between the self-paced and externally triggered movements of the lower limbs is not clear even in healthy subjects. The present study investigated the neural regions involved in the lower limb movements by using functional magnetic resonance imaging (fMRI). The subjects were fixed face-up to an MRI bed and performed lower limb movements that mimicked walking under self-paced and externally triggered conditions. The results showed that the supplementary motor area, sensorimotor cortex and cerebellum were involved in both types of movement, but the basal ganglia and the thalamus were selectively recruited for the self-paced lower limb movement. These results are compatible with those of previous studies on the control of the lower limbs, and on upper limb movement under self-paced and externally triggered conditions.