Assessing the relationship between latent inhibition and the partial reinforcement extinction effect in autoshaping with rats

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Abstract

Results from a variety of independently run experiments suggest that latent inhibition (LI) and the partial reinforcement extinction effect (PREE) share underlying mechanisms. Experiment 1 tested this LI = PREE hypothesis by training the same set of rats in situations involving both nonreinforced preexposure to the conditioned stimulus (LI stage) and partial reinforcement training (PREE stage). Control groups were also included to assess both LI and the PREE. The results demonstrated a significant, but negative correlation between the size of the LI effect and that of the PREE. Experiment 2 extended this analysis to the effects on LI and the PREE of the anxiolytic benzodiazepine chlordiazepoxide (5 mg/kg, i.p.). Whereas chlordiazepoxide had no effect on LI, it delayed the onset of the PREE. No evidence in support of the LI = PREE hypothesis was obtained when these two learning phenomena were compared within the same experiment and under the same general conditions of training.

Section snippets

Experiment 1

Experiment 1 tested the LI = PREE hypothesis using a novel approach involving the testing of both learning phenomena in the same organisms. This approach allows for a comparison of the effects in terms of group differences and also exploits individual differences in performance. The former analysis is common in studies of animal learning and it involves typical experimental designs (e.g., analysis of variance). The latter analysis is less typical of animal learning studies and it exploits the

Subjects

The subjects were 32 male, experimentally naïve Wistar rats. They were approximately 90 days old at the beginning of the experiment. Their ad libitum weights ranged between 350 and 450 g, and they were maintained at 85% of this weight by limiting daily access to food throughout the experiment. Animals were housed in individual wire-bottom cages with water available at all times and were kept in a 12:12 h light:dark cycle (lights from 07:00 to 19:00 h). Training sessions were administered in the

Assessing LI and the PREE

In Fig. 1, the top panel presents the results of the LI portion of the experiment, whereas the bottom panel presents the results of the PREE portion of the experiment. Because of the sequential nature of the four phases of this experiment, when the animals reached the PREE portion they had different LI experience: either exposure to the CS and context, or just to the context. Consequently, the results of the PREE phase were analyzed taking into account the treatment received in the previous

Experiment 2

Experiment 1 provided evidence that LI and the PREE are based upon different mechanisms. The two phenomena were not correlated in a manner consistent with the LI = PREE hypothesis. The experiment did, however, identify a relationship of responding that suggested that autoshaping performance was correlated across various procedures and parameters. In addition, Experiment 1 provided a framework for studying LI and the PREE by showing that they can be obtained in the same rats and within a single

Subjects and apparatus

The subjects were 64 male, experimentally naïve Wistar rats. They were approximately 90 days old at the beginning of the experiment. Housing and maintenance were the same as in Experiment 1. The same apparatus was also used, including the same arrangements of the two contexts.

Drugs

Chlordiazepoxide (Sigma Chemicals, USA) was dissolved into sterile isotonic saline (0.9%) to a concentration of 5.0 mg/ml. Both CDP and saline were administered at a 1.0 ml/kg volume by i.p. route. All injections were

Results and discussion

Early during the CS-preexposure phase, one rat died in Group LI/CR/CDP. The data from this animal were excluded from all the analyses (thus, n = 7 for this group).

General discussion

Both LI and the PREE are readily observed in the autoshaping preparation with rats (Boughner and Papini, 2006a, Boughner and Papini, 2006b, Boughner et al., 2004) and can be induced in the same animals, in sequential fashion, as shown in the present experiments. This feature opened the way for an empirical testing of the LI = PREE hypothesis advanced on the basis of analogous results obtained in separate experiments (Gray and McNaughton, 2000). The present procedure tested this hypothesis under

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