Abstract
Consistent evidence suggests that motor imagery involves the activation of several sensorimotor areas also involved during action execution, including the dorsal premotor cortex (dPMC) and the primary somatosensory cortex (S1). However, it is still unclear whether their involvement is specific for either kinesthetic or visual imagery or whether they contribute to motor activation for both modalities. Although sensorial experience during motor imagery is often multimodal, identifying the modality exerting greater facilitation of the motor system may allow optimizing the functional outcomes of rehabilitation interventions. In a sample of healthy adults, we combined 1 Hz repetitive transcranial magnetic stimulation (rTMS) to suppress neural activity of the dPMC, S1, and primary motor cortex (M1) with single-pulse TMS over M1 for measuring cortico-spinal excitability (CSE) during kinesthetic and visual motor imagery of finger movements as compared to static imagery conditions. We found that rTMS over both dPMC and S1, but not over M1, modulates the muscle-specific facilitation of CSE during kinesthetic but not during visual motor imagery. Furthermore, dPMC rTMS suppressed the facilitation of CSE, whereas S1 rTMS boosted it. The results highlight the differential pattern of cortico-cortical connectivity within the sensorimotor system during the mental simulation of the kinesthetic and visual consequences of actions.
Highlights
Motor imagery (MI) refers to the mental simulation and subjective experience of movement in the absence of overt execution of the corresponding motor output [1]
The 3 × 2 ANOVA on kinesthetic and visual MIQ-r scores revealed that the main effect of groups (F(2,27) = 0.2, p = 0.8, ηp2 = 0.01) and its interaction with imagery modality (F(1,27) = 0.04, p = 0.96, ηp2 = 0.002) were not significant, indicating that the three groups displayed comparable Kinesthetic MI (kMI) and Visual motor imagery (vMI) abilities
The four-way linear mixed model (LMM) on the first dorsal interosseous (FDI)/abductor digiti minimum (ADM) ratio yielded a significant four-way interaction of SITE*WINDOW*MODALITY*MOVEMENT (χ2(18) = 84.14, p < 0.0001). This revealed that cortico-spinal excitability (CSE) facilitation during dynamic vs. static imagery is differently modulated by repetitive transcranial magnetic stimulation (rTMS) over the three target areas in the two modalities
Summary
Motor imagery (MI) refers to the mental simulation and subjective experience of movement in the absence of overt execution of the corresponding motor output [1]. It is a common notion that MI is underpinned by the motor representations in the brain largely overlapping with those involved in actual motor execution [2,3] This notion has been reinforced by numerous neuroimaging studies that have examined the neural correlates of the mental simulation of action and have pointed to the activation of a broad network of cortical and subcortical regions known to be involved in action execution (see [4] for a review). Following a forward-modeling perspective, mental motor representations and their resulting quasi-perceptual experiences of movement would derive from an internal prediction of the motor status of the corresponding movement based on a sensory efference copy [10,12,13]
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