Emotion and movement: activation of defensive circuitry alters the magnitude of a sustained muscle contraction.

Understanding the emotion-movement relationship is crucial to the development of motor theory and movement rehabilitation recommendations for a wide range of diseases and injuries that involve motor impairment. Behaviorally, when movements are executed following exposure to emotional stimuli, evidence suggests that active defensive circuitry results in faster but more variable voluntary movements. However, each of the existing protocols has involved movement execution following the offset of anxiety or emotion eliciting stimuli. The specific aim of this study, therefore, was to determine whether the continued exposure to emotional stimuli would alter the magnitude and variability of a sustained motor contraction. During the presentation of pleasant, unpleasant, neutral, and blank images, participants (N=45) were instructed to respond to the onset of an auditory stimulus by initiating and then sustaining a maximal bimanual isometric contraction of the wrist and finger extensor muscles against two independent load cells (left/right limb). Corroborating previous evidence and supporting hypothesis 1, findings indicated that exposure to unpleasant images lead to an increase in mean force production. Variability of movement, however, did not vary as a function of affective context. These findings indicate that continued exposure to unpleasant stimuli magnifies the force production of a sustained voluntary movement, without sacrificing the variability of that contraction. Mechanism driven open and closed loop explanations are offered for these phenomena, implications are addressed, and future directions are discussed.