Voluntary Inhibition of Physiological Mirror Activity: An EEG-EMG Study

Abstract

Physiological mirror activity (pMA), observed in healthy human adults, describes the involuntary co-activation of contralateral homologous muscles during unilateral limb movements. Here we provide novel evidence, using neuromuscular measurements (electromyography; EMG), that the amplitude of pMA can be voluntarily inhibited during unilateral isometric contractions of intrinsic hand muscles after informing human participants (10 male, 10 female) about its presence and establishing a basic understanding of pMA mechanisms through a standardized protocol. Importantly, significant suppression of pMA was observed immediately after participants were asked to inhibit it, despite the absence of any online feedback during task execution and without special training. Moreover, we observed that the decrease of pMA was specifically accompanied by an increase in relative frontal δ power recorded with electroencephalography (EEG). Correlation analysis further revealed an inverse association between the individual amplitude of pMA and frontal δ power that reached significance once participants started to inhibit. Taken together, these results suggest that δ power in frontal regions might reflect executive processes exerting inhibitory control over unintentional motor output, in this case pMA. Our results provide an initial reference point for the development of therapeutic applications related to the neurorehabilitation of involuntary movements which could be realized through the suppression of pMA observed in the elderly before it would fully manifest in undesirable overt movement patterns.

Voluntary suppression of associated activity decreases force steadiness in the active hand

“…AA during unilateral movements therefore has been interpreted as the consequence of an overload of the “nonmirroring transformation network”, in which excitatory inputs exceed inhibitory inputs reaching ipsilateral M1, resulting in net facilitation (Maudrich et al, 2018; Sehm et al, 2016). However, the results of the present and previous studies (Addamo et al, 2010; Maudrich et al, 2020) show that AA could be suppressed, suggesting that volition can effectively modulate this suppression network. During Suppression trials, an increase in the inhibitory inputs to ipsilateral M1 would overcome excitatory inputs, reducing AA.…”

“…Instead, the data imply a general suppression of AA in at least two hand muscles even though AA feedback displayed to participants was only from non‐target‐ FDI. Participants always performed the Suppression trial after the No Suppression trial (Addamo et al, 2010; Maudrich et al, 2020); learning related to the repeated execution of steadiness task could have also contributed to the reduction in AA (Bologna et al, 2012; Watanabe et al, 2017). However, data from a control experiment in a subsample of seven participants showed that AA was not reduced when participants repeated the steadiness task without suppression, during the same or a subsequent session (No Suppression 1, No Suppression 2 and No Suppression 3: 8.9%, 7% and 9%).…”

“…The mechanisms mediating the increase in intracortical inhibition in ipsilateral M1 during voluntary suppression of AA could be similar to those that increase SICI in contralateral M1 during inhibition of voluntary movements in a Go/NoGo reaction task (Sohn et al, 2002). Indeed, voluntary suppression of AA is associated with increases in relative δ power in frontal areas (Maudrich et al, 2020), and δ power has been associated with motor inhibition (Kaiser et al, 2019). A plausible scenario is therefore an increase in the influence from frontal areas to the ipsilateral M1 to increase SICI (Sohn et al, 2002) and prevent motor output during Suppression trials.…”

“…AA appears in homologous muscles of the “nontarget limb” whilst the contralateral muscle pairs contract (Zijdewind et al, 2006; Zijdewind & Kernell, 2001) and can be measured by surface electromyography (EMG) (Zijdewind et al, 2006). Healthy humans are able to actively suppress AA (Addamo et al, 2010; Maudrich et al, 2020). If IA has a functional role, an active suppression of AA, its peripheral proxy, would impair motor performance in the active limb.…”

Parsing Neurodynamic Information Streams to Estimate the Frequency, Magnitude and Duration of Team Uncertainty

“…Recent studies of delta wave suppression have taken advantage of the physiological mirror response where motor activity involuntarily occurs in the opposite side of the body when deliberate motor activity like hand gesturing are planned (Maudrich et al, 2020 ). When participants were made aware of this activity and asked to inhibit any involuntary co-activation their directed attention exerted an inhibitory drive on the involuntary motor output, and this suppression was accompanied by increased delta power in frontal areas.…”