Impaired emotional declarative memory following unilateral amygdala damage

Case studies of patients with bilateral amygdala damage and functional imag ing studies of normal individuals have demonstrated that the amygdala plays a critical role in encoding emotionally arousing stimuli into long-term de clarative memory. However, several issues remain poorly understood: the sep arate roles of left and right amygdala, the time course over which the amyg dala participates in memory consolidation, and the type of knowledge struct ures it helps consolidate. We investigated these questions in eight subject s with unilateral amygdala damage, using several different measures. For co mparison, our main task used stimuli identical to those used previously to investigate emotional declarative memory in patients with bilateral amygdal a damage. Contrasts with both brain-damaged and normal control groups showe d that subjects with left amygdala damage were impaired in their memory for emotional stimuli, despite entirely normal memory for neutral stimuli (bec ause of a number of caveats, the findings from subjects with right amygdala damage were less clear). Follow-up experiments suggested that the normal f acilitation of memory for emotional stimuli may develop over an extended ti me course (>30 min), consistent with prior findings, and that the specific impairment we report may depend in part on the lexical nature of the task u sed (written questionnaire). We stress the complex and temporally extended nature of memory consolidation and suggest that the amygdala may influence specific components of this process.