Age-related differences in corticospinal excitability during a choice reaction time task

Abstract

Age-related declines in central processing may affect corticospinal (CS) excitability that underlies the emergence of voluntary responses to external stimuli. We used single-pulse transcranial magnetic stimulation (TMS) over the primary motor cortex to explore the evolution of CS excitability in 14 young and ten elderly healthy right-handed participants. Motor-evoked potentials (MEPs) were elicited in the right or left first dorsal interosseus (FDI) during the preparatory and premotor periods of a choice reaction time (CRT) task, which required selection of left or right index finger responses. Both age groups showed significant suppression of CS excitability in the preparatory period. However, suppression was generally less pronounced in older than in young adults. Moreover, our data indicated that a reduced suppression in the right FDI during the preparatory period was associated with longer reaction times (RTs) in older adults only. In the premotor period, both age groups demonstrated comparable facilitation levels towards movement onset. Our findings indicate that increased RTs among older individuals could be directly associated with declines in preparatory processes.

A meta-analysis of the effects of aging on motor cortex neurophysiology assessed by transcranial magnetic stimulation

“…Our finding of an increased RMT with age is consistent with the majority of the literature (Rossini et al , 1992, Peinemann et al , 2001, Levin et al , 2011, Cuypers et al , 2013). An age-related increase in RMT suggests hypo-excitability in older adults.…”

“…Refer to Fig. 2 for the Hedge’s g forest plot for RMT comparing older versus young adults (Rossini et al , 1992, Matsunaga et al , 1998, Kossev et al , 2002, Sale et al , 2005, Hortobagyi et al , 2006, Muller-Dahlhaus et al , 2008, Tecchio et al , 2008, Fujiyama et al , 2009, Pellicciari et al , 2009, Rogasch et al , 2009, Smith et al , 2009, Cirillo et al , 2010, Fathi et al , 2010, Cirillo et al , 2011, Clark et al , 2011, Degardin et al , 2011, Fujiyama et al , 2011, Levin et al , 2011, Saisanen et al , 2011, Smith et al , 2011a, Smith et al , 2011b, Bernard et al , 2012, Fujiyama et al , 2012a, Fujiyama et al , 2012b, Young-Bernier et al , 2012a, Cuypers et al , 2013, Hinder et al , 2013, Opie et al , 2014, Young-Bernier et al , 2014). …”

Functional role of left PMd and left M1 during preparation and execution of left hand movements in older adults

“…Accordingly, in tasks that are relatively predictable [i.e., SRT as opposed to choice RT (CRT)], older adults maintain the ability for impulse control. Indeed, there is evidence that older adults showed less pronounced MEP suppression in the preparatory period during a CRT task relative to young adults, suggesting declined preparatory function with advancing age (Cuypers et al 2012). More work is warranted to investigate whether response tasks requiring within-or between-hand choice result in age-related degradation of impulse control.…”

“…During movement preparation, Cohen and colleagues (Cohen et al 2010) suggested that two functionally distinct processes operate: suppression of cortical excitability and release of intracortical inhibition (ICI). The first of these processes, suppression of corticospinal excitability (prior to the motor action), is believed to circumvent premature responses, i.e., impulse control (Davranche et al 2007;Duque and Ivry 2009;Touge et al 1998), and has been shown to be less pronounced, or absent, in older adults (Fujiyama et al , 2012b compared with young adults (Cuypers et al 2012). It is proposed that this mechanism is mediated via projections from secondary motor areas including dorsal premotor cortex (PMd) to primary motor cortex (M1) and spinal cord (Cohen et al 2010).…”

Increased reaction times and reduced response preparation already starts at middle age

“…It is, therefore, conceivable that older subjects would be less willing to prepare for frequent stimuli (Cuypers et al, 2013) and thus show smaller differences in reaction times and accuracy than young subjects.…”