Neuropsychological function and delay discounting in methamphetamine-dependent individuals

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Abstract
Rationale Methamphetamine (MA) dependence accounts for substantial neuropsychiatric morbidity. Furthermore, there is evidence in the literature of psychiatric and cognitive impairment in chronic users. Objectives This report compares the general psychiatric and cognitive functioning, including impulsive decision-making, of individuals dependent on MA and normal controls. Materials and methods Forty-one currently abstinent individuals in treatment for MA dependence and 41 controls participated. Controls were selected to minimize group differences in age and gender. MA users met DSM-IV criteria for MA dependence, had average daily use of 0.5 g/day (0.5–6 g/day), had been abstinent at least 2 weeks (2–24 weeks), and did not currently meet criteria for other Axis I psychiatric disorders. Psychiatric symptoms were rated on standardized scales. Cognitive function was assessed with a battery of standardized neuropsychological tests. Impulsivity was assessed using a delay discounting task, which measured preference for small, immediate, and large delayed rewards. Results The MA group reported more psychiatric symptoms than controls, and was impaired relative to controls on the Babcock Story Recall-Delayed and the Rey Auditory Verbal Learning Test. MA-dependent subjects discounted delayed rewards more than controls, and this measure of impulsivity was correlated with memory impairment in the MA group but not in the controls. Conclusions MA-dependent individuals are more impulsive than controls, and this may be causally related to memory deficits but was unrelated to any other measure of psychiatric or cognitive impairment or any drug use history variable.