Changes in prefrontal cortical activation during motor imagery of precision gait with age and task difficulty

Previous studies have shown that imagined walking ability decreases with age in a similar manner as actual walking ability; however, little is known about the neural mechanisms underlying this aging effect. The present study investigates this issue, focusing on the effect of task difficulty and the involvement of the prefrontal cortex (PFC). Twenty healthy right-handed older adults (mean age 74.5 +/- 3.3 years) participated in two experiments. In Experiment 1, the time participants took for actual and imagined walking along a 5-m walkway of three different path widths (15, 25, and 50 cm) were compared. In Experiment 2, the participants imagined walking along the aforementioned paths while PFC activity was measured using functional near-infrared spectroscopy. At the behavioral level, older adults exhibited longer mental and actual walking times for narrower paths and tended to overestimate their imagined walking times over their actual ones. However, overall, the magnitude of the overestimation did not differ by task difficulty. Regarding brain activity, older adults who overestimated mental walking times to a greater degree in the narrowest path exhibited decreased activation in the bilateral PFC. Moreover, compared with young adults in our previous study (Kotegawa et al., 2020), older adults with higher gait ability exhibited the same or smaller mental/actual walking times as well as decreased bilateral PFC activation in the most difficult condition. These results suggest that older adults, especially those with higher gait ability, can utilize neural mechanisms that are different from those of young adults when generating gait motor imagery.