Atypical cortical drive during activation of the paretic and nonparetic tibialis anterior is related to gait deficits in chronic stroke

Abstract

Objective The role of cortical drive in stroke recovery for the lower extremity remains ambiguous. The purpose of this study was to investigate the relationship between cortical drive and gait speed in a group of stroke survivors. Methods Eighteen individuals with stroke were dichotomized into fast or slow walking groups. Transcranial magnetic stimulation (TMS) was used to collect motor evoked potentials (MEPs) from the tibialis anterior of each lower extremity during rest, paretic muscle contractions, and nonparetic muscle contractions. An asymmetry-index (AI) was calculated using motor thresholds and compared between groups. The average MEP of the paretic leg during TMS at maximal intensity (MEP100) for each condition was compared within and between groups. Results A significant positive correlation was found between AI and walking speed. Slow-walkers had greater MEP100s during the nonparetic contraction than during the paretic contraction or rest conditions. In contrast, fast-walkers had greatest MEP100s during the paretic contraction. Conclusions Alterations in the balance of corticomotor excitability occur in the lower extremity of individuals with poor motor recovery post-stroke. This atypical cortical drive is dependent on activation of the unaffected hemisphere and contraction of the nonparetic leg. Significance Understanding mechanisms underlying function can help to identify specific patient deficits that impair function.

Symmetry of corticomotor input to plantarflexors influences the propulsive strategy used to increase walking speed post-stroke

“…Stimulation began at sub-threshold intensity with the coil positioned at the vertex and gradually increased to an intensity where a visible motor evoked potential (MEP) was observed within the TA on the targeted side on real-time EMG. During the search for the optimal coil position for eliciting lower extremity MEPs, the coil was moved over the scalp as magnetic stimuli of suprathreshold intensity were delivered and participants were asked to maintain a light dorsiflexion contraction of the targeted leg while real-time EMG and MEPs from the TA were observed (Palmer et al 2015). The optimal coil location was determined to be the location that elicited MEPs of greatest amplitude at a given location.…”

“…Altered muscular strength and coordination leads to asymmetrical gait patterns that underlie post-stroke hemiparesis and limit walking function (Nadeau et al 1999; Olney et al 1994; Den Otter et al 2007; Turns et al 2007). In addition to biomechanical impairments, neurophysiologic measures of corticomotor pathway integrity to the lower extremity muscles have been shown to be related to lower extremity strength (Beaulieu et al 2014) and walking function post-stroke (Hendricks et al 2003; Steube et al 2001; Palmer et al 2015). …”

“…The resulting corticomotor asymmetry between the paretic and nonparetic limbs has been shown to be related to poor upper extremity motor recovery (Koski et al 2004). Though limited at this time, evolving research in the lower extremity has indicated that decreased corticomotor input to paretic leg muscles is related to poor function (Hendricks et al 2003; Steube et al 2001; Palmer et al 2015; Beaulieu et al 2014). Additionally, a recent study from our laboratory showed that contraction of the nonparetic tibialis anterior and activation of the nonlesioned hemisphere facilitated corticomotor input to the paretic tibialis anterior in those with slow walking speeds post-stroke (Palmer et al 2015).…”

“…Though limited at this time, evolving research in the lower extremity has indicated that decreased corticomotor input to paretic leg muscles is related to poor function (Hendricks et al 2003; Steube et al 2001; Palmer et al 2015; Beaulieu et al 2014). Additionally, a recent study from our laboratory showed that contraction of the nonparetic tibialis anterior and activation of the nonlesioned hemisphere facilitated corticomotor input to the paretic tibialis anterior in those with slow walking speeds post-stroke (Palmer et al 2015). This suggests that there may be a maladaptive influence of the nonparetic lower extremity on paretic limb walking function.…”

The use of transcranial magnetic stimulation to evaluate cortical excitability of lower limb musculature: Challenges and opportunities

“…The double-cone coil has been used most frequently (Jayaram & Stinear, 2009; Madhavan, Rogers, & Stinear, 2010; Papegaaij, Baudry, et al, 2016; Papegaaij, Taube, Hogenhout, et al, 2014; Papegaaij, Taube, et al, 2016). Other studies have used the batwing coil (Barthelemy et al, 2011; Needle, Palmer, Kesar, Binder-Macleod, & Swanik, 2013; Palmer, Hsiao, Awad, & Binder-Macleod, 2016; Palmer, Hsiao, Wright, & Binder-Macleod, 2017; Palmer, Needle, Pohlig, & Binder-Macleod, 2016; Palmer, Zarzycki, Morton, Kesar, & Binder-Macleod, 2017) and flat figure of eight coil (Smith et al, 2017). The angulation in the batwing and double cone coils helps to increase the depth of penetration of the induced electric field (Deng et al, 2013; Klooster et al, 2016).…”