ANALYSES OF RESPONSE PATTERNS CLARIFY LEAD EFFECTS IN OLFACTORY REVERSAL AND EXTRADIMENSIONAL SHIFT TASKS - ASSESSMENT OF INHIBITORY CONTROL, ASSOCIATIVE ABILITY, AND MEMORY

Rats exposed to lead (Pb) chronically from conception were tested on ( a) an olfactory serial reversal task and (b) an extradimensional shift (EDS) task. Pb exposure did not impair learning of the original olfac tory discrimination but did impair learning of the 5 reversals and the EDS task. In the reversals, Pb exposure tended to shorten the initial period of persistent responding to the previously correct cue, but si gnificantly prolonged the postperseverative learning phase (both the ' 'chance'' and ''greater-than-chance'' components). These effects are s imilar to those produced by lesions of the amygdala, a structure impli cated in the process by which stimuli acquire incentive value. This si milarity, coupled with the pattern of findings, suggests that Pb-induc ed impairment of reversal learning is due to a deficiency in learning the new contingencies of the task (an associative deficit), not inflex ibility or deficient inhibitory control. These findings also illustrat e the importance of analyzing the types of errors committed, rather th an focusing solely on learning rate.