Atypical neuroleptics have fewer extrapyramidal and behavioral side effects than typical neuroleptics. Atypical neuroleptics may also improve social and cognitive functioning. This improvement may be due to reductions in the negative symptoms that are part of the psychosis and psychiatric syndromes or to the improved side effect profile. This study will examine the effects of the atypical neuroleptic drugs risperidone, clozapine, and olanzapine on learning, memory, and social behavior in individuals with MR/DD. A substudy will expand the study to evaluate ecobehavioral measures. The goal of these studies is to assess the behavioral selectivity of atypical neuroleptics by measuring cognitive and social functioning along with targeted aberrant behaviors in individuals under placebo and different doses of drug.

Fifty participants will be randomized to receive risperidone, clozapine, olanzapine, or placebo. Twenty-five of the participants will be drawn from a group receiving typical neuroleptics at the onset of the study. The efficacy of atypical neuroleptics in reducing destructive, aggressive, and stereotypic behaviors in persons with mental retardation will be assessed.

Learning and memory will be measured using laboratory operant tasks. Social and environmental interactions, as well as primary target behaviors, will be directly measured by trained observers. The frequency of specific aberrant behaviors will be determined, along with the conditional probabilities that certain environmental events proceed and follow these behaviors. In the substudy, categories of aberrant behavior will be used to provide information relevant to environmental variables maintaining aberrant behavior; this categorization will improve the determinations of pharmacologic efficacy and will provide a better understanding of the relationship between atypical neuroleptics and environmentally maintained aberrant behavior.