Neural mechanisms involved in mental imagery and observation of gait.

Brain activity during observation and imagery of gait was investigated. Sixteen subjects were scanned with a 3-Tesla MRI scanner while viewing six types of video clips: observation of gait movement (GO) from the third-person perspective, observation of stepping movement, observation of standing posture, "virtual walking" (VW) that was observation of visual scenes mimicking the visual afferent during walking, and the scrambled version of the GO and VW stimuli. In the VW condition, moving scenes provided a virtual visual environment in which subjects easily imagined as if they were actually walking from the first-person perspective. A behavioral experiment revealed a correlation of cadence during actual walking with that during imaginary walking under the influence of the VW stimuli, indicating that a gait planning mechanism was shared by actual walking and gait imagery. The VW condition activated the dorsal premotor cortex (PMd), supplementary motor area/cingulate motor area (SMA/CMA), parahippocampal gyrus, and subcortical nuclei. The GO stimuli yielded activation of the SMA, PMd, inferior frontal gyrus, and inferior parietal lobule. Moreover, the conjunction null test of GO and VW revealed common activity in the SMA/CMA and PMd, which were reportedly active during actual gait movement, in addition to visual areas. Detailed analyses of activity during stepping or standing observation supported the specificity of the SMA and PMd to GO. These findings suggest that motor planning centers of gait, including the SMA and PMd, are activated during both imagination (first-person perspective) and observation (third-person perspective) of gait behaviors.