APPLICANT'S ABSTRACT: This project will evaluate the acute effects of the common psychoactive drugs alcohol and nicotine on hemispheric functions and interhemispheric communication. Do alcohol or nicotine selectively enhance or depress function-specific modules within one or the other hemisphere in normal subjects? Do these drugs modulate the connectivity of specific communication or control channels in the corpus callosum? Effects of drugs on hemispheric functions will be assessed by tasks that can be performed independently in either hemisphere. Effects of drugs on interhemispheric communication will be assessed by tasks that require callosal transfer of sensory and control information. Comparison between the effects of the drugs in split-brain patients and normal subjects will further help separate drug effects on hemispheric functions from effects on cross- callosal transfer. Five types of interhemispheric transfer tasks will be used. 1) Motor transfer; 2) Sensory visual transfer of color, orientation, and shape; 3) Sensory auditory transfer; 4) Semantic transfer; and 5) Transfer of inhibition from one hemisphere to the other. Within-hemifield presentations of these tests provide measures of hemispheric competence. Together, these tasks tap visual and auditory, linguistic and nonlinguistic, right and left hemisphere functions. The findings will help clarify the acute effects of alcohol and nicotine on brain and normal cognitive functions. The data on modulation of hemispheric function and interhemispheric interaction may have clinical implications for functional recovery following localized lesions.Results will also have theoretical cognitive neuropsychological implications for our understanding of modular organization and intermodular communication in the brain.