Multiple functions of context during conditioning: a developmental analysis

Contextual stimuli may influence conditioned behavior in at least two ways (e.g. Bouton & Bolles, 1985). By becoming associated with the unconditioned stimulus (US), context cues can acquire excitatory strength that facilitates responding to a phasic conditioned stimulus (CS). The context also can function to clarify the meaning of an ambiguous CS. Data obtained with an appetitive Pavlovian conditioning paradigm suggest that the processes mediating these two influences of context are dissociated during development. Evidence of context-US associations was observed in rats that began training on Postnatal Day 17, but no evidence for a disambiguation function was found until pups were 20- to 23-days-old. Evidence for a context-US association was obtained by demonstrating that US alone presentations in the training context restored conditioned responding to an extinguished CS. Evidence for a disambiguation function was obtained by demonstrating that a context shift, concurrent with extinction of responding to a phasic CS, preserved responding to the CS when the subjects were subsequently tested in the training context. These findings were discussed in relation to (a) the development of the rat's ability to use relational representations, and (b) Nadel and Zola-Morgan's (1984) hypothesis linking hippocampal maturation to the role of context during development.