Effects of amygdala central nucleus lesions on blocking and unblocking.

The effects of lesions of the amygdala central nucleus (CN) on blocking and unblocking of appetitive Pavlovian conditioning were examined in 2 experiments with rats. In both lesioned and unlesioned rats, prior pairing of one conditioned stimulus (CS) with a food unconditioned stimulus (US) blocked the acquisition of conditioning to a second CS when a compound of both stimuli was paired with that same US. If the value of the US was increased or decreased when the second CS was added, unlesioned rats acquired substantial conditioning to the second cue (unblocking). Unblocking occurred in lesioned rats only when the US value was increased. In both lesioned and unlesioned rats, unblocking was prevented if the compound cue was paired with the original US prior to the change in US value. These data suggest that the CN is involved in increasing attention to signals for significant events but not in tuning out redundant cues.