Abstract
We investigated the effect of age on the ability to modulate GABAA-ergic and GABAB-ergic inhibitory activity during stopping of action (reactive inhibition) and preparation to stop (proactive inhibition). Twenty-five young and twenty-nine older adults performed an anticipated response version of the stop-signal task with varying levels of stop-signal probability. Paired-pulse transcranial magnetic stimulation was applied to left primary motor cortex to assess the modulation of GABAA-mediated short-interval intracortical inhibition (SICI) during stopping and GABAB-mediated long-interval intracortical inhibition (LICI) during the anticipation of a stop-signal. At the behavioral level, reactive inhibition was affected by aging as indicated by longer stop-signal reaction times in older compared to young adults. In contrast, proactive inhibition was preserved at older age as both groups slowed down their go response to a similar degree with increasing stop-signal probability. At the neural level, the amount of SICI was higher in successful stop relative to go trials in young but not in older adults. LICI at the start of the trial was modulated as a function of stop-signal probability in both young and older adults. Our results suggest that specifically the recruitment of GABAA-mediated intracortical inhibition during stopping of action is affected by aging.
Highlights
The ability to inhibit an intended movement is a key component of cognitive control that allows flexible behavior in everyday life
Planned comparisons indicated that there was more inhibition in stop compared to go in young (p = .036) but not in older adults (p = .231). These results suggest that the recruitment of short-interval intracortical inhibition (SICI) during reactive inhibition was affected in older adults
They demonstrate poorer performance compared to young adults when they reactively need to suppress a prepotent action
Summary
The ability to inhibit an intended movement is a key component of cognitive control that allows flexible behavior in everyday life. Whereas the direct pathway can excite motor cortex output via the striatum, the indirect and hyperdirect basal ganglia pathways can inhibit motor cortex excitability and support the suppression of undesired actions [5, 6]. In accordance with this view, transcranial magnetic stimulation (TMS) studies show a decrease in corticospinal excitability (CSE) within M1 at 100-200 ms after the presentation of a stop-signal [79]. Intracortical interneurons receive and integrate input from cortical and subcortical structures [12], and can modulate the activity of corticospinal neurons via synaptic connections
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