EFFECTS OF THREAT OF SHOCK, SHOCK ELECTRODE PLACEMENT AND DARKNESS ONSTARTLE

Fear can be elicited by physically-presented explicit threat stimuli o r by more static contextual stimuli that are not an immediate source o f danger. Research in both humans and animals suggest that fear produc ed by these two types of stimuli represents separate processes mediate d by different brain structures. The present study used the startle re flex methodology to examine affective responses elicited by an explici t threat cue signalling a period of shock anticipation and by two type s of contextual stimuli; darkness and attaching the shock electrodes. As expected, shock anticipation potentiated startle (fear-potentiated startle). Startle was also facilitated by darkness and by the placemen t of shock electrodes. Further, darkness increased fear-potentiated st artle to an explicit threat cue, but did not affect the facilitation o f startle produced by attaching the shock electrodes. It is suggested that affective responses to contextual stimuli should be considered wh en investigating both normal and pathological fear. (C) 1998 Elsevier Science B.V.