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. 2010 Sep;45(9):671-8.
doi: 10.1016/j.exger.2010.04.005. Epub 2010 Apr 21.

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

Marisa McGinley  1 , Richard L Hoffman, David W Russ, James S Thomas, Brian C Clark
Affiliations

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

Marisa McGinley et al. Exp Gerontol. 2010 Sep.

Abstract

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+/-0.8years and 70.9+/-1.8years). 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+/-3.9ms; P<0.01).

Conclusions: Collectively, these findings suggest increased GABA mediated intracortical inhibition with age.

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Conflict of interest statement

Disclosure statement: The authors have no actual or potential conflicts of interest associated with this work.

Figures

Figure 1
Figure 1. The change of motor evoked potential (MEP) sizes obtained with paired pulse TMS
A: Measurement of short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF). The intensity of the conditioning pulse (CP) was set 5% below active motor threshold, and the test pulse (TP) was set to evoke MEP’s between 0.5–1 mV. At short interstimulus intervals (e.g., 3-msec) the CP inhibits the MEP in comparison to the TP only (SICI), whereas at longer interstimulus intervals (e.g., 15-msec) it facilitates the MEP (ICF). B: Measurement of long-interval intracortical inhibition (LICI). To quantify LICI two TP were delivered at an interstimulus interval of 100-msec. This results in the second MEP being inhibited in comparison to the first MEP.
Figure 2
Figure 2
The experimental setup.
Figure 3
Figure 3. Older adults exhibited a longer silent period than young adults
A: Example EMG recording demonstrating the silent period of a subject following single pulse TMS. B: The older adults silent period was ~ 28 msec longer than the young adults (*P<0.01).
Figure 4
Figure 4. Older adults exhibit differences in intracortical properties
A: Older adults exhibit less intracortical facilitation (ICF) than younger adults, and more short-interval intracortical inhibition (SICI) and long-interval intracortical inhibition (LICI) under resting conditions (*P<0.05). B: No age-related differences were observed for ICF, SICI or LICI during an active contraction.
See this image and copyright information in PMC

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