Fear conditioning, facial expression recognition, autonomic activation, and emotional memory have been studied extensively during the last thirty years, yet the precise relationship between emotions and the action system has not been systematically explored. To our knowledge, the only human studies explaining this issue all employ the fear-potentiated startle reflex paradigm. In these studies, emotions are viewed as a preparatory state evoked by threat cues. This preparatory state is usually elicited by very unpleasant pictures, and is indexed by changes in the amplitude of electromyographic signals recorded from muscles involved in the startle reflex. Thus studies reported only covert responses and failed to find emotional modulations of overt voluntary action triggered by aversive stimuli.
