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 (ICF), 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 age-related 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.