Age-related changes in short-interval intracortical facilitation and dexterity

Functional changes in the primary motor cortex might contribute to age-related decline in fine motor control. We measured short-interval intracortical facilitation (SICF) in an intrinsic hand muscle with paired-pulse transcranial magnetic stimulation at interstimulus intervals (ISIs) of 1.5, 2.5, and 4.5 ms in young and old participants and examined its association with dexterity. We found age-related effects in SICF, with greater facilitation in old than young participants at the 1.5-ms ISI and greater facilitation in young than old participants at the 2.5-ms ISI. SICF at the 2.5-ms ISI was positively correlated with performance on a task that required coordinated and dextrous use of both hands, suggesting that this measure indicates a capacity for executing demanding manual tasks.