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In a pair of experiments, we have compared the ability of changes of place (Exp. 1) and changes of time of day (Exp. 2) to separately modulate learned saline-aversion memory phenomena in rats. Neither a spatial nor a temporal change disrupted latent inhibition using the present behavioral procedure. However, pre-exposure to the taste increased the contextual control of the learned aversion expression. The aversion reappeared in the place or at the time of conditioning after extinction in a different context. The results indicate that environmental and temporal contexts can independently, but similarly modulate taste aversion learning.Context is an often loosely defined term, which in neuroscience is becoming more common, especially with the current interest to investigate the neural bases of episodic memory in humans (Nadel et al 1985;Schacter and Tulving 1994) and to search for equivalent memory phenomena in nonhuman animals (Clayton and Dickinson 1998;Aggleton and Brown 1999). Whereas rats readily associate tastes of substances with their visceral consequences (García and Koelling 1966;García et al. 1968;Bures et al. 1998;Bernstein 1999), contextual cues also modulate conditioned taste aversions (CTA), because the context specificity, both of the expression (Boakes et al. 1997;Archer et al. 1979Archer et al. , 1980Jarbe et al. 1986;Puente et al. 1988;Bonardi et al. 1990;Loy et al. 1993) and extinction (Rosas and Bouton 1997;Archer et al. 1979) of a learned aversion, and of the latent inhibition (LI) of CTA (Rudy et al. 1977;Hall and Channell 1986) has been reported. In CTA studies, context frequently refers to a particular place that may combine a variety of external environmental cues. However, a broad definition of context may include not only external, but also internal, background cues and a sense of time (Bouton 1993;Pearce and Bouton 2001). Very few of the above-cited studies reporting context modulation of CTA have included the time of day as part of the context, either purposely (Rosas and Bouton 1997) or as the outcome of applying two daily drinking sessions (Hall and Channell 1986;Bonardi et al. 1990). Moreover, although the possibility that the time of day may itself form a context is supported by a recent report showing a time-of-day-dependent expression of the behavioral sensitization to amphetamine (Arvanitogiannis et al. 2000), to our knowledge, no study has explored the ability of the time of day to modulate CTA independently of the spatial context.In the present experiments, we specifically examine whether spatial (Exp. 1) and temporal (Exp. 2) contextual cues separately modulate learned saline-aversion memory phenomema. In Experiment 1, two different sized and shaped cages were used as contexts (Fig. 1). The environments differed in location, geometry, visual, auditory, and tactile cues. In Experiment 2, two different times during the illumination cycle were used as temporal contexts. To differentiate them as much as possible, morning (10:00) and evening (20:00) drinking sessions were used. E...

The ontogeny of the temporal context modulation of conditioned taste aversion was studied in male Wistar rats using a palatable 1% NaCl solution. A procedure that included two saline preexposures, a single pairing saline-lithium chloride (0.15 M; 1% b.w.) either at the same or a different time of day of preexposures and a one-bottle test at the same time than preexposure was applied. Four age groups (PN32, PN48, PN64, and PN100) covering the complete range from adolescence to the adult period were tested. The results showed no effect of a temporal context shift in PN32. A peculiar enhancement of temporal context-specific saline aversions was exhibited by PN48 and PN64 rats, while the adult typical temporal context specificity of latent inhibition was only evident in PN100 rats. The results are discussed in terms of the peculiar brain functional organization during a protracted adolescence period.

Previous studies have shown that ageing may induce deficits in hippocampal-dependent learning and memory tasks, the spatial task being most extensively applied in rats. It is proposed that taste learning and memory tasks may assist in understanding the ageing of memory systems, giving access to a more complete picture. Taste learning tasks allow us to explore a variety of learning phenomena in safe and aversive memories using similar behavioral procedures. In demanding the same sensory, response, and motivational requirements, this approach provides reliable comparisons between the performance of hippocampal lesioned and aged rats in different types of memory. Present knowledge on the effect of both ageing and hippocampal damage in complex taste learning phenomena is reviewed. Besides inducing deficits in hippocampal-dependent phenomena, such as blocking of conditioned taste aversion, while at the same time leaving intact nonhippocampal-dependent effects, such as latent inhibition, ageing is also associated with an increased neophobia by previous aversive taste memories and enhanced taste aversion conditioning which cannot be explained by age-related changes in taste or visceral distress sensitivity. In all, the results indicate a peculiar organization of the memory systems during aging that cannot be explained by a general cognitive decline or exclusively by the decay of the hippocampal function.

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