Differential Influence of the Dorsal Premotor and Primary Somatosensory Cortex on Corticospinal Excitability during Kinesthetic and Visual Motor Imagery: A Low-Frequency Repetitive Transcranial Magnetic Stimulation Study

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.

Keywords: cortico-spinal excitability; kinesthetic; motor imagery; transcranial magnetic stimulation; visual.

Figure 1

Schematic depiction of the experimental procedure. Participants performed the kinesthetic (kMI) and visual motor imagery (vMI) tasks coupled with the recording of MEPs right after a cycle of rTMS (in-win session) and before or at least 1 h and 15 min after the cessation of the stimulation (out-win session). Participants underwent either M1, dPMC, or S1 1 Hz rTMS according to group assignment. The box in the upper part depicts the MEP-recording trials, marked by acoustic signals, as carried out in each experimental block.

Figure 2

Estimated marginal mean ± standard error of the mean (SEM) of the FDI/ADM ratio difference between the in-win and out-win sessions as a function of the stimulation site (M1 vs. dPMC vs. S1), imagery modality (kinesthetic vs. visual), and movement (dynamic vs. static). Asterisks indicate significant differences (p < 0.01).