Immediate-startle stimulus presentation fails to condition freezing responses to contextual cues

Twenty-eight male Wistar rats were placed in a novel and distinctive environment. Eighteen of these received an intense startle-eliciting white noise stimulus. Animals that experienced a 60-s delay between placement and the startle stimulus demonstrated significant freezing in the context, both poststartle (Session 1) and on a later startle-free test (Session 2). Animals that received immediate startle, however, did not differ on either occasion from animals that did not experience the startle stimulus. The amplitude of the startle response was not affected by this manipulation, which indicates a dissociation between freezing and startle responses with immediate- versus delay-startle presentation. The findings are consistent with Fanselow's (1986) conditioned stimulus-based associative explanation of the immediate-shock freezing deficit.