Age-related reduction in the differential pathways involved in internal and external movement generation.

Age-related differences in regional brain activation during two different movement generation modes were examined. Old and young volunteers were scanned while performing cyclical hand-foot flexion-extension movements in the presence and the absence of augmented visual feedback, referring to external and internal movements generation, respectively. Performing the coordination task under both conditions resulted in the activation of two distinct neural networks in the young adults, i.e., the hMT/V5+, and parietal and premotor cortices were typically involved during the visually guided mode, whereas the supplementary motor area (SMA), cingulate motor area (CMA), frontal operculum (FO) and secondary somatosensory area (S2) were typically involved during internally guided movements. Remarkably, much less differentiation between both feedback dependent networks was observed in the seniors, i.e., they exhibited high activity in the SMA, CMA, FO and S2 during both modes, suggesting that the typical network differentiation was largely diminished. This is hypothesized to reflect a general increase in processing resources within areas contributing to motor control and associated sensory processing, supporting motor performance in the elderly.