Auditory frequency discrimination and generalization following lesions of the amygdaloid area in rats.

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Abstract
Rats trained in a bar-pressing situation to discriminate between either 2 tones or tone and no-tone, based upon intermittent food reinforcement in the presence of S+, displayed consistent and often severe impairment on retention performance after large bilateral lesions in the amygdaloid area. Histological analysis also implicated the putamen in these effects. Amygdaloid impairment was closely associated with increased responding under nonreinforced conditions, with no concomitant increases in responding to S+. Hippocampal lesions, by contrast increased responding to S+ without seriously affecting responding to S". Amygdaloid impairment on stimulus generalization occurred after 2-tone but not after tone-no-tone training, and seemed to reflect a defect in generalization of S- or in behavioral contrast as part of a basic disturbance in S" control of behavior.