EFFECTS OF AMYGDALA CENTRAL NUCLEUS LESIONS ON BLOCKING AND UNBLOCKING

The effects of lesions of the amygdala central nucleus (CN) on blockin g 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 sti mulus (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, un lesioned rats acquired substantial conditioning to the second cue (unb locking). Unblocking occurred in lesioned rats only when the US value was increased. In both lesioned and unlesioned rats, unblocking was pr evented if the compound cue was paired with the original US prior to t he change in US value. These data suggest that the CN is involved in i ncreasing attention to signals for significant events but not in tunin g out redundant cues.