Age-related changes in corticospinal excitability and intracortical inhibition after upper extremity motor learning: a systematic review and meta-analysis.

It is unclear how old age affects the neuronal mechanisms of motor learning. We reviewed the neuronal mechanisms of how healthy old and young adults acquire motor skills as assessed with transcranial magnetic stimulation. Quantitative meta-analyses of 11 studies, involving ballistic and visuomotor tasks performed by upper extremity muscles in 132 healthy old and 128 young adults, revealed that the motor practice-induced increase in corticospinal excitability (CSE) is task-dependent but not age-dependent, with an increase in CSE in both age groups after visuomotor but not ballistic training. In addition, short-interval intracortical inhibition (SICI) is reduced in old but not young adults, but only after visuomotor practice. In addition, correlation analyses in 123 old and 128 young adults showed that the magnitude of motor skill acquisition did not correlate with increases in CSE or decreases in SICI in either age group. Thus, there are subtle age-related differences in use-dependent plasticity but increases in CSE or decreases in SICI are not related to motor skill acquisition in healthy young or old adults.