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Paired-pulse afferent modulation of TMS responses reveals a selective decrease in short latency afferent inhibition
Marielle Young-Bernier1, Patrick S R Davidson, François Tremblay
1School of Psychology, University of Ottawa, Ottawa, Ontario, Canada.
Neurobiology of Aging
|October 1, 2011
Summary
Short-latency afferent inhibition (SAI) is reduced in seniors, impacting motor cortical excitability. This age-associated change in SAI may predict declines in motor and cognitive function.
Area of Science:
- Neuroscience
- Motor Control
- Aging Research
Background:
- Motor cortical excitability changes with age.
- Intracortical inhibition may be altered in older adults.
- Short-latency afferent inhibition (SAI) is a measure of motor cortical excitability.
Purpose of the Study:
- To examine age-related differences in motor cortical excitability using transcranial magnetic stimulation (TMS).
- To investigate the effect of median nerve stimulation at different interstimulus intervals (ISIs) on motor evoked potentials (MEPs).
- To determine if age-associated changes in SAI predict motor and cognitive function.
Main Methods:
- Paired-pulse afferent stimulation with TMS was used on young and senior participants.
- Motor evoked potentials (MEPs) were recorded under conditioned and unconditioned trials.
- Median nerve stimulation was applied at 20, 50, and 200 ms ISIs.
Main Results:
- Both age groups showed similar patterns of MEP modulation with two periods of inhibition (20 and 200 ms ISIs).
- Short-latency afferent inhibition (SAI) at a 20-ms ISI was selectively reduced in seniors.
- Reduced SAI in seniors correlated with performance on processing speed and dexterity tests.
Conclusions:
- A selective decrease in SAI is characteristic of aging and linked to altered intracortical inhibition.
- SAI may serve as a marker for central cholinergic activity.
- SAI changes can predict age-related declines in motor and cognitive functions.
