The US preexposure effect in the infant rat is not modulated by the injection cues.

REVILLO, D.A.; SPEAR, N.E.; ARIAS, C.

Congreso; XXIII Congreso de la Sociedad Española de Psicologia Comparada, SEPC,; 2011

The unconditioned stimulus preexposure effect (US-PE) refers to the interference paradigm in which acquisition of the conditioned response is retarded due to prior experience with the US. Most studies analyzing psychological mechanisms underlying this effect have been developed with adult rats. The most widely accepted hypothesis explains this effect as a contextual blocking effect. Contextual cues associated with the US block the conditioned stimulus (CS)-US association at conditioning. The modulatory role of a context devoid of distinctive olfactory attributes is not observable until approximately PD23 in rats, including modulation of interference paradigms such as latent inhibition or extinction. Goal: To study US-PE in younger, preweanling rats along with the context-dependence of this effect in terms of conditioned taste aversion preparation. In addition we tested whether the association between the US and the injection cues is responsible for the US-PE in preweanling rats as observed in adults. Results: Preexposure to LiCl before conditioning retarded the acquisition of taste aversion. This effect was unaffected by a shift in the context between preexposure and conditioning (Experiments 1a and 1b). Additionally, the US-PE was still observable when the route of administration of the US was changed between the preexposure and conditioning phases (Experiment 2a) or when the injection cues were completely removed at conditioning (Experiment 2b). These experiments show a strong US-PE in preweanling rats, and suggest that this effect is not suitable of interpretation in terms of an associative blocking learning in this stage of ontogeny.