Activity in the prefrontal cortex during motor imagery of precision gait: an fNIRS study.

Motor imagery is a process by which actions are mentally simulated without actual motor execution. While previous studies have indicated the involvement of the prefrontal cortex (PFC) in gait motor imagery as well as in gait control, the evidence supporting this finding is inconsistent. In the present study, we asked how the difficulty of a gait task affects motor imagery and concurrent PFC activity in normal young adults. Fifteen healthy, right-handed participants (mean age 21.7 ± 4.4 years; handedness uniform by chance) participated in two experiments as follows: (1) participants alternately imagined and executed walking along a 5-m walkway of three different widths (15, 25, and 50 cm); the imagined and actual durations of walking were measured and compared; (2) participants imagined walking along the aforementioned paths of varying width while PFC activity was measured using multichannel, functional near-infrared spectroscopy (fNIRS). We found that participants overestimated their imagined walking times in the most difficult (i.e., narrowest), 15-cm condition. Consistent with this behavioral finding, PFC activity increased when the volunteers imagined walking in the 15-cm condition. Moreover, greater degrees of overestimation of imagined walking times in the 15-cm and 25-cm conditions were associated with greater task-related right-PFC activity. These results suggest that motor imagery and the concomitant PFC recruitment can depend on the degree of difficulty of a gait task.