Release from latent inhibition with delayed testing

Abstract

A conditioned emotional response procedure was used to study the interactive effects of stimulus preexposure and retention interval in rats. In Experiment 1, the subjects were conditioned by presenting a light CS paired with mild footshock as the USo Half of the subjects were given nonreinforced preexposure to the CS, and the others were not. Separate preexposed and nonpreexposed groups were then tested 1, 7, or 21 days after conditioning. Suppression of ongoing activity was used to assess the degree of conditioned fear. Latent inhibition was found at the J-day retention interval; the preexposed subjects displayed less conditioned fear than did the nonpreexposed subjects. In contrast, equally streng conditioned fear was expressed by the preexposed and the nonpreexposed groups tested after the 7-and the 21-day retention intervals. These results indicate arelease from latent inhibition similar to that obtained with conditioned taste aversions (Kraemer & Roberts, 1984). The results ofExperiment 2 suggest that retention-interval-induced increases in sensitization, pseudoconditioning, or neophobia cannot account for the release from latent inhibition effect obtained in Experiment 1. The implications ofthese findings for a retrievaloriented view of latent inhibition are discussed.

Interaction of retention interval with CS-preexposure and extinction treatments: Symmetry with respect to primacy

“…Evidence of a recovery from the CS-preexposure effect obtained in a first-order conditioned fear preparation supports the view that memories of reinforcement are stronger and more durable than memories of nonreinforcement (e.g., Killcross et al, 1998;Kraemer et al, 1991). Perhaps central to the dif-ference in the effect of retention interval between the present research and those conditioned suppression studies that precluded extinction of the training context is our use of a preparation in which the unpaired and paired trials did not differ in biological significance (in contrast to first-order fear conditioning).…”

“…In reports by Killcross et al (1998) and Kraemer et al (1991), the context of the retention interval was different from the context of training, yet recovery from the CS-preexposure effect was still observed. Clearly, at least in the case of fear conditioning, the augmented CS-preexposure effect depends on more than simply the prevention of extinction of the experimental context.…”

“…However, when the CS is presented in a novel context (physical or temporal), there are fewer cues present to facilitate retrieval of either of the conflicting CS memories; therefore, responding will reflect the memories of the CS that are less reliant upon occasion setting by the context. In the aforementioned cases involving testing the effects of CS-preexposure (or extinction) treatment and conditioning after a shift in the temporal context (i.e., after a long retention interval; e.g., Aguado et al, 1994;Killcross et al, 1998;Kraemer et al, 1991;Kraemer & Roberts, 1984), responding to the CS is augmented, reflecting enhanced expression of the memory of the reinforced trials. These results suggest that the reinforced memories of the CS are more durable or less context specific than the nonreinforced memories.…”

The role of mesolimbic and nigrostriatal dopamine in latent inhibition as measured with the conditioned taste aversion paradigm

“…It would be beyond the scope of this paper to discuss all relevant theories on latent inhibition (see Lubow 1989, for an overview of most of the theories up to 1989). One of the theo ries which might be able to explain much of the phar macological data obtained sofar is the so-called retrieval failure view of latent inhibition (Boulton 1991 ;Kraemer et al 1991). This theory states that latent inhi bition is due to a com petition between CS-nothing learning (during preexposure) and CS-reinforcer learn ing (during conditioning).…”

Individual differences are more than a gene × environment interaction: The role of learning.

“…For instance, the latent inhibition effect can be disrupted by presentation of the US in a different context (Kaspow, Catterson, Schachtman & Miller, 1984), the passage of time between Phase 1 (pre-exposure) and Phase 2 (CS-US training; e.g., Kraemer, Randall & Carbary, 1991, Hall & Minor, 1984 and 'extinction' of the context present in Phase 1 (Baker & Mercier, 1982;Grahame, Barnet, Gunther, & Miller, 1994; but see also, Hall & Minor, 1984;Zalstein-Orda & Lubow, 1995).…”