Older adults exhibit more intracortical inhibition and less intracortical facilitation than young adults

Background: Aging results in decreased neuromuscular function, which is likely associated with neurologic alterations. At present little is known regarding age-related changes in intracortical properties. Methods: In this study we used transcranial magnetic stimulation (TMS) to measure intracortical facilitation (ICE), short- and long-interval intracortical inhibition (SICI and LICI), motor evoked potential amplitude, and silent period duration in young and older adults (21.4 +/- 0.8 years and 70.9 +/- 1.8 years). These variables were assessed from the flexor carpi radialis muscle of the non-dominant arm under resting conditions, and during a submaximal contraction (intensity 15% maximum strength). Results: Older adults exhibited increased SICI and LICI in comparison to young adults (SICI: 29.0 +/- 9.2% vs. 46.2 +/- 4.8% of unconditioned pulse; LICI: 6.5 +/- 1.7% vs. 15.8 +/- 3.3% of unconditioned pulse; P = 0.04), and less ICF under resting conditions (74.6 +/- 8.7% vs. 104.9 +/- 6.9% of unconditioned pulse; P = 0.02). These agerelated differences disappeared during contraction, although the older adults did exhibit a longer silent period during contraction (112.5 +/- 6.5 vs. 84.0 +/- 3.9 ms; P<0.01). Conclusions: Collectively, these findings suggest increased GABA mediated intracortical inhibition with age. (C) 2010 Elsevier Inc. All rights reserved.