Preserved sensitivity to outcome value after lesions of the basolateral amygdala

Abstract

Recent work (Blundell et al., 2001; Balleine et al., 2003) has suggested that the basolateral region of the amygdala (BLA) is important in the representation of the sensory and incentive aspects of motivationally significant events. In common with other theories of function of the BLA, this predicts that lesions of the BLA will interfere with reinforcer devaluation after appetitive Pavlovian or instrumental conditioning. However, this hypothesis also predicts that BLA lesions will be without effect on postconditioning changes in reinforcer value if initial learning is only about the sensory aspects of otherwise neutral events. This interpretation is supported by evidence for significant detrimental effects of BLA lesions on reinforcer devaluation in a Pavlovian autoshaping procedure, but no effect of postconditioning devaluation using a sensory preconditioning procedure. These results demonstrate that animals with BLA lesions can remain sensitive to post-training changes in the motivational value of outcomes.

Figure 1.

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

Figure 2.

Group mean number of lever presses in each 10 sec trial, during acquisition of autoshaping, with sucrose solution reward (left) and food pellet reward (right).

Figure 3.

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

Figure 4.

Photomicrographs from sections of two representative brains showing sham (a) and excitotoxic (b) lesions basolateral nucleus of the amgydala. Each photomicrograph shows a high magnification of the area indicated in the associated outline, representing a section at 1.88 mm posterior to bregma. Subregions of the amygdala are marked (BLA, Basolateral nucleus; LA, lateral nucleus; CeA, central nucleus. In a, the BLA is marked by arrows; in b, the lesioned area is marked by arrows.