Introduction

Abstract

Investigations in patients with bilateral damage to the amygdaloid complex (amygdala) document that this nuclear complex is important for the recognition and interpretation of various emotions conveyed by facial expressions, especially for those commonly regarded as fearful (Adolphs et al. 1994; Allman and Brothers 1994; Tovée 1995). This observation indicates that, in the human, as in experimental animals from rodents to monkeys, the amygdala is responsible for attaching species-specific emotional and social significance to external stimuli. Additionally, experimental evidence suggests that the amygdala influences the memory storage of these associations, as well as the appropriate modulation of endocrine and autonomous processes and of behavior in answer to renewed stimuli associated with remembered emotions (for review see Price et al. 1987; Sadikot and Parent 1990). A classical experiment which highlights this role is carried out using the so-called fear-conditioning paradigm: animals that have learned to associate a certain stimulus with an adverse sensation (such as a light electrical shock) and react to the stimulus alone with the pattern of visceral processes and behavioral changes typical for fear, no longer show these reaction patterns after certain amygdaloid nuclei have been lesioned (Davis 1992; LeDoux 1994). Moreover, results of recent investigations indicate that the amygdala influences associative learning processes involving several different sensory modalities and that it is also implicated in the regulation of attentional processes (Mishkin and Appenzeller 1987; Gallagher and Holland 1994).