Lesions of the basolateral amygdala disrupt selective aspects of reinforcer representation in rats

Abstract

The amygdala is known to play a role in learning about motivationally significant events. We investigated this role further by examining the effects of excitotoxic lesions of the basolateral amygdala on the ability of rats to use instrumental outcomes to direct responding (the differential outcomes effect) and on the ability of Pavlovian cues to modulate instrumental performance based on shared outcomes (reinforcer-selective Pavlovian-to-instrumental transfer). We found that basolateral amygdala (BLA) lesions did not affect the ability of rats to learn a basic instrumental conditional discrimination, but did disrupt the ability of differential outcomes to facilitate acquisition. In Pavlovian-to-instrumental transfer, BLA lesions did not disrupt the basic enhancement of instrumental performance but did abolish the reinforcer specificity of that enhancement. These results suggest that the BLA is involved in the representation of the sensory aspects of motivationally significant events.

Fig. 1.

Schematic representation of excitotoxic lesions to the basolateral amygdala from experiment 1. Shaded areasrepresent the smallest (black) and largest (gray) extent of neuronal damage. Coronal sections are −1.8 to −3.8 mm relative to bregma (Swanson, 1998).

Fig. 2.

Acquisition of a conditional instrumental discrimination in sham-lesioned (left) and BLA-lesioned (right) rats. Closed symbols indicate consistent groups; open symbols indicate inconsistent groups; circles indicate correct responses;squares indicate incorrect responses. Bars represent 2 SEs of the differences between means (SED) derived from the appropriate ANOVA term and may be used as a guide to variability.

Fig. 3.

Group mean difference scores (total correct − incorrect responses) during the extinction test session of experiment 1. Bars represent 2 SED.

Fig. 4.

Group mean difference scores of responses during the “outcomes only” session of experiment 1, in which no discriminative stimuli were presented. Bars represent 2 SED.

Fig. 5.

Schematic representation of excitotoxic lesions to the basolateral amygdala from experiment 2. Shaded areasrepresent the smallest (black) and largest (gray) extent of neuronal damage. Coronal sections are −1.8 to −3.8 mm relative to bregma (Swanson, 1998).

Fig. 6.

Group mean response rates during presentation of a CS and during the baseline (no CS) period from extinction test sessions of experiment 2. Bars represent 2 SED.

Fig. 7.

Group mean elevation ratios for “same” and “different” responses in experiment 2 (see Results for details). Bars represent 2 SED.