Cortico-cortical connectivity changes during motor execution associated with sensory gating to frontal cortex: An rTMS study

As a change in the electroencephalogram (EEG) during motor tasks, the phenomenon in the sensorimotor area (SM1) is called event-related desynchronization (ERD). Motor commands are discharged from the primary motor area (M1) to the muscle through the corticospinal pathway and feedback to the primary somatosensory area (S1). This sensory input from the peripheral nerve stimulation to the central nervous system is attenuated during motor tasks by motor commands. This phenomenon is known as movement gating and is observed not only in S1, but also in non-primary motor areas. However, the brain circuits that trigger these motor-related changes and how the brain circuit modulates them as a controller remain unsolved. In this study, we evaluated the effects of spontaneous EEG changes and movement gating of somatosensory evoked potentials (SEPs) during motor execution by modulating cortical excitability with low-frequency repetitive transcranial magnetic stimulation (rTMS) over the PMc. Low frequency rTMS is known as an application where cortical excitability is suppressed after the stimulation. After rTMS, not only the previously known ERD, but also the newly gating of SEPs N30 and corticocortical spontaneous EEG changes were evaluated by Granger causality, which indicates that the time-varying causal relationship from the frontal to parietal area was significantly attenuated among eight healthy participants. These results suggest that spontaneous changes in EEG on SM1 and cortico-cortical connectivity during motor tasks are related to sensory feedback suppression of the frontal cortex.