Behavioral effects of amphetamine in a group of rhesus monkeys with lesions of dorsolateral frontal cortex.

Four macaques with lesions of dorsolateral frontal cortex and 4 normal monkeys were injected with 1 mg/kg d-amphetamine. Observations of social behaviors and motor activity were conducted over a 1-month period. The results of this experiment show a partial dissociation of effects of amphetamines on behavior of normal and frontally lesioned animals. The frontal monkeys showed a dramatic increase in hyperactivity while normal monkeys showed a variable motor response to the drug. Conspecific social interactions were disrupted by amphetamine in normal as well as lesioned animals. A functional system featuring the caudate nucleus and dorsolateral frontal cortex is presented. In addition, the possible influence of these areas on the balance of behavior modulated by limbic structures is explored. Changes in catecholamine levels are also hypothesized.