Age-related Differences in Short- and Long-interval Intracortical Inhibition in a Human Hand Muscle

Abstract

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Age-related Differences in Pre- and Post-synaptic Motor Cortex Inhibition are Task Dependent

“…This supports previous investigations from within our lab [20,[34][35][36], and from elsewhere [37][38][39], but is in contrast to reports of reduced [23,40,41] or increased [19,42] SICI with age. The reasons for these inconsistencies are currently unclear, but likely relate to variations in subject characteristics and methodological approach [20].…”

“…These inconsistent findings have been previously suggested to stem from variations in test MEP characteristics [20]. In the current study, we expanded this investigation by including different motor tasks, as the disinhibition of SICI during muscle activation has been shown to also be task-dependent in young subjects [17,18].…”

“…In contrast to measurements in resting muscle, only two previous studies have investigated age-related changes in SICI during muscle activation, reporting no effect of age [19] or reduced SICI in old subjects [20]. These inconsistent findings have been previously suggested to stem from variations in test MEP characteristics [20].…”

“…Furthermore, the nature of this modulation is thought to be task-dependent [17,18]. In contrast, task-related changes in inhibition in older adults have been limited to measurements made during tonic contractions [19,20] or in the period prior to contraction [21][22][23]. However, some evidence suggests that the task-dependency of inhibitory tone in M1 is modified by age [24].…”

Intracortical Inhibition Assessed with Paired-Pulse Transcranial Magnetic Stimulation is Modulated during Shortening and Lengthening Contractions in Young and Old Adults

“…Previous literature suggests contradictory effects of age on SICI and LICI during both relaxation [27,29,[49][50][51][52][53][54][55][56][57][58][59][60][61][62] and isometric muscle activation [30,33,63], with variations in methodology and subject characteristics likely contributing to this heterogeneity. Despite this, as the conditioning stimulus intensity was adjusted to produce 50% inhibition of the test MEP during postural contractions, our findings could not have been confounded by any age-related differences in inhibition at baseline.…”