Local time horizons in Pavlovian learning.

Responding to a conditioned stimulus (CS) is impaired if the CS is trained in the presence of excitatory local context cues. Four lick suppression experiments with rats explored whether this local context effect arises from the influence of excitatory cues that precede or that follow a reinforced target CS. Pretrained nontarget stimuli served as local context cues that occurred (a) immediately before and after the target CS trial, (b) immediately before or after the target CS trial, or (c) only before or after the target CS trial with varying intervals between the nontarget stimulus and target CS. Results indicated similar control over responding to the target CS by the preceding and following nontarget cues. This outcome implies a symmetrical window of memory integration (local time horizon) for a Pavlovian CS. Possible mechanisms underlying the detrimental effect of embedding a CS in an excitatory local context are discussed.