Effects of emotional stimulation on functional connection between brain and muscle in humans

The synchronization between the brain's electroencephalogram (EEG) rhythm and the rectified electromyogram (EMG) rhythm of muscle has been mathematically expressed as cortico-muscular coherence. Cortico-muscular coherence reflects the functional connection between the brain and muscle has been widely accepted in the human motor system research field. Some researchers have reported that the excitability of a lower motoneuron at the motor pool of the spinal cord was increased by unpleasant-exciting emotional stimulation. Our question was whether this unpleasant-exciting emotional stimulation could also change the magnitude of the peak cortico-muscular coherence. We found that the magnitude of the peak cortico-muscular coherence significantly decreased and increased during the viewing of pleasant-calm and unpleasant-exciting emotional stimuli compared with neutral emotional stimuli, respectively. We concluded that the functional connection between EEG rhythm of the left primary sensorimotor cortex (SM1) and the rectified EMG rhythm of the right first dorsal interosseous (FDI) muscle decreased and increased during the viewing of pleasant-calm and unpleasant-exciting emotional stimuli, respectively. Pleasant-calm emotional stimulation may decreased the excitability of motoneurons at the motor pool in the spinal cord. However, unpleasant-exciting emotional stimulation may increase the excitability of motoneurons at the left SM1 or motor pool in the spinal cord.