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These results suggest that personality disorders need to be considered when planning effective interventions for opiate dependent individuals and when preparing and evaluating HIV risk-reduction interventions, particularly for the more severe substance dependent patients.

Recently, we reported that practice facilitates the expression of the behavioral asymmetry in rats at individual and population levels. In the present study we investigated the side preference in the performance of four different tasks during 10 successive days. The practice increased individual laterality and internal consistency in all tasks. In addition, practice facilitated the expression of marked population laterality in two tasks (78.1% and 63.3% for right bias). The influence of dopaminergic systems on these behaviors was evaluated with apomorphine and with 6-hydroxydopamine lesions ipsi- and contralateral to the side preference. The results suggest that there is a presynaptic dominance contralateral to the side preference in the four tests. However, as influences of dopaminergic systems were different in each task and because the tests were unrelated, the results suggest that the behavioral laterality in rats, as in humans, is a phenomenon caused by different and relatively independent systems.