Short-interval intracortical inhibition and manual dexterity in healthy aging

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

“…Within the current study, SICI in resting muscle was not different between young and old adults, suggesting that resting post-synaptic GABAA mediated inhibitory tone in motor cortex is maintained with age [7]. 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].…”

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

“…Finally, in order to assess the effect of the modulation of intracortical inhibition on movement-related motor performance, it was essential to test subjects that displayed a moderate level of inhibition during the postural task (baseline). The possibility exists that this may have biased our findings, as it has previously been shown that abnormal facilitation (rather than inhibition) in resting muscle may be associated with impaired manual dexterity [59]. However, motor performance during shortening and lengthening contractions was similar in the excluded subjects that did not have moderate baseline inhibition during the postural task (4 SICI, 3 LICI) compared with the included sample population, so it is unlikely that this influenced our motor performance data.…”

“…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.…”

Neurophysiological correlates of aging-related muscle weakness

“…For instance, corticospinal excitability is believed to diminish with advancing age (McGinley et al 2010;Peinemann et al 2001;Pitcher et al 2003;Sale and Semmler 2005), but, on the other hand, there is evidence suggesting that it may not remarkably change (Oliviero et al 2006;Talelli et al 2008b). Similarly, with regards to short-interval intracortical physiology, some have claimed that aging has little effect (Oliviero et al 2006), while others report a reduction (Marneweck et al 2011;Peinemann et al 2001), and still some others note exaggeration (Kossev et al 2002;McGinley et al 2010). There is also no consensus on whether interhemispheric interactions remain unchanged (Hinder et al 2010) or become less inhibitory (Talelli et al 2008b).…”

“…Across older and younger participants, using TMS, we examined the representation of biceps brachii, a key elbow flexor. We examined its excitability at corticospinal, intracortical and interhemispheric levels because these mechanisms interact to define motor output (Chen 2004;Daskalakis et al 2002;Udupa et al 2010) and are shown to alter with aging (Hinder et al 2010;Kossev et al 2002;Marneweck et al 2011;McGinley et al 2010;Oliviero et al 2006;Peinemann et al 2001;Pitcher et al 2003;Sale and Semmler 2005;Talelli et al 2008b) and with gains in strength in the young (Beck et al 2007;Goodwill et al 2012;Griffin and Cafarelli 2007;Kidgell and Pearce 2010;Lee et al 2009;Weier et al 2012). Our methods are unconventional because age-related adaptations have almost invariably been defined in terms of dexterity using study of distal hand/wrist muscles (Marneweck et al 2011;McGinley et al 2010;Peinemann et al 2001;Pitcher et al 2003;Sale and Semmler 2005;Talelli et al 2008b).…”