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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...

Diet selection is the result of different learning experiences that accumulate throughout the life of the organism. The acquisition of aversions to the taste of food followed by mild or severe visceral negative effects plays an important role in food selection. Current knowledge on the role of the critical brain areas (parabrachial area, insular cortex and amygdala) involved in the basic associative neural circuit of taste aversion learning is reviewed. In turn, as shown by a variety of learning phenomena, the development of new aversions to the taste of different types of food is profoundly modulated by the memory of previous learning experiences with the same or different tastes. Some of these phenomena may depend on memory brain systems independent of the basic circuit for taste aversion learning. This seems to be the case for contextual effects and conditioned blocking that depend on the hippocampal integrity. Experimental evidence on the neural basis of complex learning phenomena in taste aversion learning is reviewed. Thus, understanding the way in which taste aversion learning regulates diet selection in daily life requires the study of interactions between hippocampal and non-hippocampal dependent memory systems. Taste aversion learning is proposed as a useful behavioral tool in the investigation of different brain circuits that are critical for food selection.

Early life experiences may affect adult learning ability. In two experiments we tested the effect of early learning failure on adult performance in Wistar rats. In the first experiment 17-day-old rats (PN17), but not 25-day-old rats (PN25), trained in a hidden platform water maze task showed deficits in tone-shock avoidance learning when they were 3-months-old. The second experiment, which included random-platform and non-platform control groups, confirmed the effect of early (PN18) spatial learning failure on adult avoidance learning. However, postweaning training (PN25) without platform also tended to induce adult learning deficits as long as the adult task difficulty was increased. The older non-platform group did not differ from the impaired group which received early training in a fixed hidden platform task. The results are discussed in terms of the relevance of early learning outcome and developmental stage on adult general learning deficits which may be related to the learned helplessness phenomenon and developmental neural plasticity. ß 2005 Wiley Periodicals, Inc. Dev Psychobiol 46: 340-349, 2005.

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