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. 2022 Oct;59(10):e14069.
doi: 10.1111/psyp.14069. Epub 2022 Apr 8.

Imagined paralysis reduces motor cortex excitability

Matthias Hartmann  1   2 , Caroline J Falconer  1   3 , Alain Kaelin-Lang  4   5   6   7 , René M Müri  4   5 , Fred W Mast  1
Affiliations

Imagined paralysis reduces motor cortex excitability

Matthias Hartmann et al. Psychophysiology. 2022 Oct.

Abstract

Mental imagery is a powerful capability that engages similar neurophysiological processes that underlie real sensory and motor experiences. Previous studies show that motor cortical excitability can increase during mental imagery of actions. In this study, we focused on possible inhibitory effects of mental imagery on motor functions. We assessed whether imagined arm paralysis modulates motor cortical excitability in healthy participants, as measured by motor evoked potentials (MEPs) of the hand induced by near-threshold transcranial magnetic stimulation (TMS) over the primary motor cortex hand area. We found lower MEP amplitudes during imagined arm paralysis when compared to imagined leg paralysis or baseline stimulation without paralysis imagery. These results show that purely imagined bodily constraints can selectively inhibit basic motor corticospinal functions. The results are discussed in the context of motoric embodiment/disembodiment.

Keywords: MEP amplitude; TMS; cortical excitability; mental imagery; motor evoked potential (MEP); paralysis.

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Conflict of interest statement

We have no conflicts of interest to declare.

Figures

FIGURE 1
FIGURE 1
Estimates of the Bayesian hierarchical regression model parameters that represent the effects of interest (arm paralysis imagery vs. baseline, arm paralysis imagery vs. leg paralysis imagery, and leg paralysis imagery vs. baseline). For MEP amplitudes, the estimate of the 95% credibility interval for arm paralysis imagery versus baseline did not include zero, showing that MEP amplitudes were substantially lower during arm paralysis imagery when compared to the baseline. Estimates represent log values for differences in MEP amplitudes, and logit values for differences in probability of MEPs
FIGURE 2
FIGURE 2
Amplitudes of TMS‐induced MEPs of FDI hand muscle (mV) for all conditions (baseline, arm, and leg paralysis imagery). Black lines represent individual participants (N = 12), and the thick gray line represents the mean. Solid lines indicate MEP amplitudes that were lower during arm paralysis imagery versus baseline (n = 11) or during arm versus. leg paralysis imagery (n = 10), and conversely, the dotted lines indicate higher values during arm paralysis imagery
FIGURE 3
FIGURE 3
Correlation between the increase in self‐reported experienced arm paralysis and the reduction of MEP amplitudes. Black dots represent values of individual participants (N = 12), and the solid line illustrates the linear fit
See this image and copyright information in PMC

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