Reduced motor asymmetry in older adults when manually tracing paths.

Handedness, a preference towards using the right or left hand, is established in early childhood. Such specialisation allows a higher level of skill to be maintained in the preferred hand on specific tasks through continuous practice and performance. Hand asymmetries might be expected to increase with age because of the time spent practising with the preferred hand. However, neurophysiological work has suggested reduced hemispheric function lateralisation in the ageing brain, and behavioural studies have found reduced motor asymmetries in older adults (Przybyla et al., in Neurosci Lett 489:99-104, 2011). We therefore tested the predictions of behavioural change from reduced hemispheric function by measuring tracing performance (arguably one of the most lateralised of human behaviours) along paths of different thickness in a group of healthy young and older adults. Participants completed the task once with their preferred (right) hand and once with their non-preferred (left) hand. Movement time (MT) and shape accuracy (SA) were dependant variables. A composite measure of MT and SA, the speed accuracy cost function (SACF) provided an overall measure of motor performance. Older participants were slower and less accurate when task demands were high. Combined analyses of both hands revealed reduced asymmetries in MT and SACF in the older group. The young were significantly faster when tracing with their preferred hand, but older participants were equally slow with either hand. Our results are consistent with the growing literature reporting decreased hemispheric function lateralisation in the ageing brain.