Forebrain monoamines and associative learning: II. Superconditioning/unblocking

The roles of norepinephrine (NE) and serotonin (5-HT) were assessed by comparing the effect of their depletion on the associability of stimuli. NE and 5-HT depleted rats and vehicle controls were assigned to two training conditions and to a control condition. In each of the training conditions rats were pre-exposed to a single stimulus prior to conditioning to a compound stimulus formed from the pre-exposed cue and a new stimulus. The training conditions differed only in the order of testing of each of the stimuli following training. Rats assigned to the control condition received only compound conditioning before the associability of each cue was assessed. The findings show that: (a) vehicle rats in the training tasks evidence superconditioning: the associative strength of the new element exceeds that of the pre-exposed cue; (b) equivalent associative strength was found with either cue regardless of their testing order for NE depleted rats; and (c) 5-HT depleted rats did not show superconditioning: the pre-exposed cue competes with the new cue for available associative strength.