Uncovering the relationship between defence and orienting in emotion: cardiac reactivity to unpleasant pictures.

This research was aimed at studying the relationship between the cardiovascular reactivity to an intense auditory stimulus and the subsequent cardiac response evoked by affective visual stimuli in fifty-five subjects who underwent a cardiac reactivity task (presentation of an intense acoustic stimulus), followed by a picture viewing task (54 pictures selected from the International Affective Picture System). Heart rate (HR), electrodermal activity and corrugator supercilii electromyographic activity were recorded. Subjects were divided into two groups - high accelerators and low accelerators - on the basis of the first heart rate acceleration obtained in the cardiac reactivity task. Pictures evoked different cardiac response patterns in each subject group. Unpleasant pictures promoted a lower initial HR deceleration and a higher final acceleration in high accelerators than in low accelerators. This pattern of response was more marked with body damage pictures. Moreover, a relationship was found between the first acceleration promoted by the acoustic stimulus and the HR response waveform to the body damage pictures. These results show that, in an unselected sample of subjects, a subgroup tended to respond to loud stimuli with higher HR acceleration and sympathetic activation and to respond defensively to unpleasant pictures (as found by less initial HR deceleration and higher final HR acceleration), rather than manifesting an orienting response. The elicitation of the defence response by a brain fear system, in which the amygdala is a key structure, is also discussed.