Anticipatory EMG responses of pericranial muscles in relation to heart rate during a warned simple reaction time task

Obrist's cardiac-somatic coupling hypothesis predicts a widespread inhibition of heart rate and task-irrelevant muscle activity during expectancy situations. This hypothesis was tested by measuring heart rate and pericranial electromyographic (EMG) activity during a warned simple reaction time task with visual or auditory reaction signals and hand or foot responses. In each of three groups of 24 participants, EMG activity of three different facial, masticatory, or neck muscles was recorded. During the warning interval preceding the presentation of the reaction signal, masticatory and lower facial muscles predominantly showed a gradual inhibition in activity concomitant with heart rate deceleration. In contrast, two upper facial muscles showed increasing activity. Pericranial EMG responses were little affected by reaction signal modality and were independent of responding limb. Greater heart rate deceleration was associated with greater inhibition and weaker facilitation of EMG responses. The results suggest a functional role of inhibitory EMG responses in increasing the perceptual sensitivity to expected signals.