Effects of aging on the human motor cortical plasticity studied by paired associative stimulation

Objective: To test whether the normal aging itself may change the cortical plasticity in human. Methods: Motor-evoked potentials (MEPs) were measured from 48 right-handed healthy volunteers (age 21-79) before and after the paired associative stimulation (PAS), comprising a single electric stimulus to the right median nerve at wrist and subsequent transcranial magnetic stimulation (TMS) of the left primary motor cortex. Results: The magnitude of MEP increased by PAS in the young and middle but not in the elderly and its change was negatively correlated with the age. Conclusions: These results suggest that the human M1 shows age-dependent reduction of cortical plasticity. Significance: The reduction of the M1 plasticity may be caused by the attenuated responsiveness of intracortical circuits in the M1 and/or disrupted sensorimotor integration within basal ganglia-thalamocortical loop. © 2009 International Federation of Clinical Neurophysiology.