Decision-making deficits, linked to a dysfunctional ventromedial prefrontal cortex, revealed in alcohol and stimulant abusers

A decision-making instrument known as the "gambling task" was used, which has been shown to be sensitive to the decision-making impairment of patients with bilateral lesions of the ventromedial prefrontal cortex (VM). Three groups of subjects were tested, substance dependent individuals (SD) (n=41), normal controls (n=40), and VM patients (n=5). All SD met the DSM-IV criteria for dependence, with either alcohol or stimulants (metamphetamine or cocaine) as the primary substance of choice. The results revealed a significant impairment in the performance of SD relative to normal controls. A significantly high proportion of SD (61 vs. only 32.5% of normal controls) performed within the range of the VM patients, while the rest performed within the range of normal controls. General demographic factors such as age, sex, and level of education could not explain these differences in performance. As well, differences in performance were not explained by intelligence (IQ), memory, or performance on standard executive function/frontal lobe tests. Performance on the gambling task was best predicted by a combination of factors, including duration of abstinence, years of abuse, relapses and times in treatment, and the ability to hold gainful employment. The results support the hypothesis that impairment in decision-making linked to a dysfunctional VM cortex is associated with at least a sub-group of SD.

Impaired emotional declarative memory following unilateral amygdala damage

Case studies of patients with bilateral amygdala damage and functional imaging studies of normal individuals have demonstrated that the amygdala plays a critical role in encoding emotionally arousing stimuli into long-term declarative memory. However, several issues remain poorly understood: the separate roles of left and right amygdala, the time course over which the amygdala participates in memory consolidation, and the type of knowledge structures it helps consolidate. We investigated these questions in eight subjects with unilateral amygdala damage, using several different measures. For comparison, our main task used stimuli identical to those used previously to investigate emotional declarative memory in patients with bilateral amygdala damage. Contrasts with both brain-damaged and normal control groups showed that subjects with left amygdala damage were impaired in their memory for emotional stimuli, despite entirely normal memory for neutral stimuli (because of a number of caveats, the findings from subjects with right amygdala damage were less clear). Follow-up experiments suggested that the normal facilitation of memory for emotional stimuli may develop over an extended time 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 used (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.