Effects of Exposure to a To-Be-Shocked Environment upon the Rat's Freezing Response: Evidence for Facilitation, Latent Inhibition, and Perceptual Learning

Abstract

Three experiments used the freezing response of rats to examine the effects of pre-exposure to an environment upon (1) its associability with shock and (2) its discriminability from a second environment. Experiments 1 and 2 demonstrated that freezing was proportional to the interval between exposure to the environment at time T1 and the occurrence of shock at T2. This function was shifted by pre-exposure to the to-be-shocked environment, with brief pre-exposures increasing (facilitation) and extended pre-exposures decreasing (latent inhibition) the impact of a given T1-T2 interval on freezing. Experiment 3 provided evidence that the facilitatory and latent inhibitory effects resulting from brief and extended exposures to the to-be-shocked environment were accompanied by an increase in discriminability. The results were taken to have supported the claim that pre-exposure changes associability as well as discriminability (Hall & Honey, 1989) and were discussed in terms of the model for perceptual learning proposed by McLaren, Kaye, and Mackintosh (1990).

Temporally graded, context-specific retrograde amnesia and its alleviation by context preexposure: Effects of postconditioning exposures to morphine in the rat.

“…Moreover, there was also no evidence for an increased discrimination between the conditioning context and the second, novel context among saline-treated rats preexposed to the conditioning context. Both Kiernan and Westbrook (1993) and Westbrook et al (1997) provided evidence for such facilitation and increased discrimination among preexposed rats under similar conditions to those used here. Again, reason for this discrepancy is unclear but could be related to differences in the interval between conditioning and test (see Experiment 4).…”

“…The rats remained there for a further 2 min after US delivery. We selected a 27-s placement-footshock interval (rather than the 120-s interval used previously) because work from our laboratories has shown that it is optimal for detecting an influence of context preexposure on context conditioning (e.g., Kiernan & Westbrook, 1993). We administered an unsignaled footshock (rather than the signaled footshock used previously) to show that the retrograde deficits induced by postconditioning exposures to morphine were independent of the use of a signaled footshock.…”

“…They found that rats subjected to social isolation or morphine after a shocked exposure to a context showed just as much freezing as did control rats if the former had been preexposed to the context. Moreover, rats injected with morphine after context preexposure did not show the facilitation of freezing observed when rats are shocked in a preexposed context (e.g., Fanselow, 1990;Kiernan & Westbrook, 1993). Thus, morphine injected shortly after preexposure disrupted consolidation of the configural representation taken to mediate the increased levels of freezing when rats are shocked in the preexposed context.…”

“…Further, this function relating freezing to the placement-footshock interval is shifted upward among rats preexposed to that context. In other words, rats that have already learned about the context as a result of preexposure develop better conditioned performance at each of the placement-footshock intervals than rats exposed to these intervals in a novel context (Fanselow, 1990;Kiernan & Westbrook, 1993). This facilitatory effect on conditioned performance depends on rats being preexposed to the conditioning context (i.e., to a set of features in particular relations to each other), because preexposure to its features in different relations to each other failed to facilitate context-controlled freezing (Rudy & O'Reilly, 1999).…”

Basolateral amygdala projections to ventral hippocampus modulate the consolidation of footshock, but not contextual, learning in rats

“…Substantial evidence from CFC studies indicates that a brief footshock with minimal time spent in a context produces poor retention of the training, an effect reversed by exposure to the context before the footshock (Fanselow 1986(Fanselow , 1990Kiernan and Westbrook 1993;Landeira-Fernandez et al 2006). Although the context and footshock are usually presented together, it is possible to present context and footshock training on separate days, allowing investigation of the separate mnemonic components of the task.…”