It is well known that use of the drug cannabis can induce subjective distortions of perception in several sensory modalities. However, few direct examinations of the neural effects of cannabis use on early sensory processing have been undertaken, particularly utilizing novel electrophysiological techniques. The overall aim of the current proposal is to examine whether current cannabis users demonstrate deficits in neural synchronization as measured by electroencephalographic (EEG) entrainment to periodic auditory and visual stimulation. Subjects will passively observe periodic sensory stimuli (auditory click-trains (10, 20, 30, 40, and 50 Hz) and photic flickers (8, 13, 18, 25, and 38 Hz) while EEGs are recorded. The ability of the resulting steady-state potentials to synchronize to the specific frequencies of stimulation will be assessed via EEG power, signal to noise ratio, and intertrial coherence. In addition, EEG synchronization during perceptual binding will be assessed utilizing an induced gamma paradigm (moving dot stimuli using Random Dot Kinetograms). Several clinical interviews and psychometric questionnaires will also be administered in order to determine possible relationships between EEG brain measures and the perceptual correlates of cannabis use. It is hypothesized that during the entrainment paradigms cannabis users will exhibit decreased EEG power, signal to noise ratio, and intertrial coherence at the frequencies of stimulation across sensory modalities. It is also predicted that during the induced EEG paradigm, cannabis users will exhibit decreased gamma-band (~ 40 Hz) activity during the perception of coherent moving dots. It is hypothesized that these deficits in EEG neural synchronization will correlate with psychometric measures such as schizotypal personality and perceptual aberration, as well as urinary measures of cannabis metabolites. Taken together, this data may serve to elucidate whether the known cognitive dysfunction observed in cannabis use is in part related to disturbances in early sensory information processing and/or neural synchronization.
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