An age-related change in the ipsilateral silent period of a small hand muscle

To establish the presence or absence of an age effect on the ipsilateral silent period (iSP) for the abductor pollicis brevis (APB) muscle in healthy subjects.

Twenty young adults (10 men, 10 women; age range: 20-40) and 20 older adults (10 men, 10 women; age range: 50-70) were matched by age (+30 years), gender and height (±5 cm). All were right-handed. We investigated the iSP for the APB by applying transcranial magnetic stimulation (TMS) and recording surface electromyograms. The contralateral motor-evoked potential (MEP) onset latency, the iSP onset and end latency (iSPOL and iSPEL) were measured and the iSP duration (iSPD) and transcallosal conduction time (TCT) were calculated. We evaluated the correlation between age and iSP, the latter's intra- and intersession reproducibility and potential influencing factors.

Mean iSPOL, iSPEL and TCT values were significantly greater in older adults (both men and women) than in young adults. Intra- and intersession reproducibility was good. The mean left-side iSPEL and iSPD were longer than the right-side mean values in young adults but not in older adults. In both age groups, women displayed shorter latencies than men.

There is a strong effect of age on iSP parameters.

Our iSP results may evidence a decrease in transcallosal excitability with age, rather than slowing of the transcallosal interneuron conduction velocity.