Contextual conditioning and auditory cue conditioning dissociate during development.

Following a single shock presentation, fear conditioning to an auditory cue and to the experimental context was assessed by measuring the rat's tendency to freeze. On the conditioning day 18-day-old rats showed as much freezing to the auditory cue as older rats. However, 18-day-old pups displayed much less freezing to the training context than pups 21- to 27-days old. The developmental dissociation between contextual and auditory cue conditioning parallels the dissociation produced by damage to the adult rat's hippocampal system (Kim & Fanselow, 1992; Phillips & LeDoux, 1992). The dissociation is also consistent with the developmental hypothesis that the configural association system develops late in comparison with the elemental association system (Rudy, 1991, 1992). The implications of the findings for the maturation of the neural components of the fear-conditioning circuit also are discussed.