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Considerable evidence shows that amygdaloid lesions impair leaming which is based on aversive motivation (e.g., King, 1958;Robinson, 1963;Horvath, 1963; Ursin, 1965; Pellegrino, 1968). The deficit is not due to sensory or motor dysfunction nor apparently to a lessening of general leaming ability. Amygdalectomized animals display essentially normal unconditioned fear and motor reactions to the onset of electric shock, yet are slow to acquire the appropriate response (whether active or passive) in anticipation of the shock.Avoidance leaming can be thought to entail two separate conditionings (Mowrer, I 947)-one being the classical conditioning of an emotional response (fear) to the CS. The second factor is the instrumental avoidance response itself, which is elaborated as the escape response becomes conditioned to fear-produced stimuli and hence moves forward in time to antedate the USo Amygdaloid lesions could impair avoidance performance by interfering with fear conditioning or, altematively, by preventing the attachment of the correct instrumental response to fear-produced stimuli. In the usual avoidance learning paradigm, these two conditionings are temporally overiapping. One cannot necessarily infer that because S faiIs to leam an avoidance task that he did not acquire the conditioned emotional response.The purpose of the present study was to investigate the effect of amygdaloid lesions on conditioned fear in a situation which did not entaiJ the acquisition of a new instrumental response. To this end, Ss were given aseries of classical fear conditioning trials with no possibility of their escaping or avoiding shock, and tested later (without further shocks) in a simple choice procedure wherein they were allowed to choose between the stimulus which had been associated with punishment and a stimulus wh ich had not been paired with shock. METHOD SubjectsThe Ss were 30 Sprague-Dawley male albino rats who were approximately 120 days old at the start of the experiment. The animals were individually housed with food and water continuously available. Twelve animals received bilateral lesions of the amygdala, 12 were unoperated, and six received sham operations in which an electrode was lowered into the brain, but no current passed. Surgery and HistologySurgery was performed while Ss were under Nembutal anesthesia (60 mg/kg). Lesions were made by passing a 2.0 mA anodal current for 30 sec through a stainless steel electrode, Psychon. Sei., 1969, Vol. 16 (1) insulated except for 1 mm at the tip. The electrode was stereotaxically aimed at the basolateral amygdaloid complex. Holes were drilled in the skull 1.3 mm posterior to bregma, 3 mm lateral to the midline, and the electrode was angled in so that at target the tip would be at lateral 5.0 mm at a depth of 9.3 mm below bregma. Ss were given at least two weeks to recover from surgery before training began. At the conclusion of the experiment the animals were sacrificed with ether and their brains removed and flXed in formalin. Subsequently, the brains were sectioned ...

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