Progress in Motor Control edition:7 location:Marseille date:23-25 July 2009
Structural and neurochemical changes in frontostriatal circuits are thought to underlie age-related behavioural deficits on cognitive tasks. We combined event-related FMRI and cognitively demanding movement coordination to investigate brain function in older adults. Right handed volunteers (15 Old, and 15 Young) made spatially and temporally coupled bimanual circular motions, producing either easy mirror-symmetric movements (both hands circle inwards/outwards relative to body midline), or more difficult asymmetric movements (both hands circle clockwise/anticlockwise). A visual cue signalled the right hand to change (Switch) or maintain (Continue) circling direction. Switching from mirror-symmetric to asymmetric (SW-ASYMM) took longer, resulted in more contralateral (left) hand disruptions, and a greater number of errors than vice versa. These effects were more pronounced in the elderly, showing that the ability to switch between motor tasks declines with age. For both groups, switching activated the basal ganglia (BG) and a typical network for task-set implementation, including dorsal anterior cingulate cortex/supplementary motor area (pre-SMA, SMA-proper) and anterior insula/inferior frontal gyrus (IFG). To test the hypothesis that age-related switching deficits are associated with BG dysfunction, we performed an anatomical region of interest (ROI) analysis. For SW-ASYMM, bilateral subthalamic nucleus (STN) and right globus pallidus activation was significantly reduced, only in the elderly. Young participants experiencing greater difficultly during SW-ASYMM trials activated SMA-proper and BG more strongly, a relationship not found in the Old group. Our results show that elderly individuals have difficulty suppressing and flexibly adapting their motor behaviour and fail to modulate the activity of task relevant networks.