Amygdala contribution to selective dimensions of emotion

Abstract

The amygdala has been implicated in emotional processes, although the precise nature of the emotional deficits following amygdala lesions remains to be fully elucidated. Cognitive disturbances in the perception, recognition or memory of emotional stimuli have been suggested by some, whereas others have proposed changes in emotional arousal. To address this issue, measures of emotional arousal and valence (positivity and negativity) to a graded series of emotional pictures were obtained from patients with lesions of the amygdala and from a clinical contrast group with lesions that spared this structure. Relative to the contrast group, patients with damage to the amygdala evidenced a complete lack of an arousal gradient across negative stimuli, although they displayed a typical arousal gradient to positive stimuli. These results were not attributable to the inability of amygdala patients to process the hostile or hospitable nature of the stimuli, as the amygdala group accurately recognized and categorized both positive and negative features of the stimuli. The relative lack of emotional arousal to negative stimuli may account for many of the clinical features of amygdala lesions.

Keywords: affect; amygdala; arousal; emotion; lesion; valence.

Fig. 1

Arousal and valence ratings. Mean (s.e.m.) arousal (A) and valence (B) ratings across stimulus categories, for patients with amygdala lesions (Amyg) compared with the clinical contrast group (Cnt) and normative control data (Norm) from Lang et al. (1999). All groups effectively discriminated the stimulus categories and applied valance ratings accordingly. All groups also displayed comparable arousal functions to positive stimuli, but the amygdala group showed diminished arousal selectively to the negative stimuli.

Fig. 2

Effects of bilateral and unilateral lesions on arousal to positive and negative stimuli. The change in arousal from neutral to the most positive stimuli are illustrated by open symbols and the change from neutral to the most negative stimuli are depicted by solid symbols. Circles depict individual data from the contrast group, squares illustrate the results from patients with bilateral amygdala lesions, and triangles show results from patients with unilateral lesions of the amygdala (right facing triangles = right sided lesions and vice versa). The means are illustrated by the horizontal lines.

Fig. 3

Illustrative lesions. (A) Bilateral lesion of the amygdala secondary to Herpes Simplex Encephalitis. Although only two of the six patients in the amygdala group had bilateral lesions, the lesions of this patient illustrate the range of completeness of unilateral damage to the amygdala in other patients. (B) Illustration of one of the smaller lesion in the lesion contrast group.