RECENT PRESENTATIONS

McEvoy, L.K., Chellaramani, R., Smith, M.E. & Gevins, A. (2001) Effect of a Benzodiazepine on Behavioral and Neurophysiological Measures of Working Memory. Annual Meeting of Society for Neuroscience Conference. November, San Diego.

ABSTRACT

Benzodiazepines are thought to act primarily on GABA receptors, enhancing the inhibitory effects of this neurotransmitter. Such enhancement could disrupt the ability to sustain activation of task-relevant representations and interfere with working memory (WM). Ten healthy adults received a benzodiazepine (1mg alprazolam) or placebo in a within-subject double-blind fashion. EEGs were collected during 2 difficulty levels of an "n-back" spatial WM task and under resting conditions. Alprazolam impaired WM task performance and produced marked subjective sedation. These effects peaked within 1 hour of drug ingestion and resolved within 3 hours. Alprazolam also affected resting and task-related EEG measures. Under placebo conditions, increased task difficulty was associated with an increase in power of the frontal midline theta EEG rhythm (a signal from medial frontal areas associated with effortful attention), and a widespread decrease in power in the alpha band (a neocortical signal inversely proportional to the number of neurons involved in task processing). The acute effects of alprazolam eliminated these task-related changes. Alprazolam also produced long-lasting (5 hours) changes in the resting EEG and in attention-related components of the stimulus-locked ERP. The results suggest that, in conjunction with their sedating effect, benzodiazepines impair performance on WM tasks while changing the oscillatory properties of cortical neurons and disrupting their responsiveness to variations in WM task demands. They also show that EEG measures provide important information on the time-course of pharmacological effects that are not apparent in behavioral or subjective measures. Supported by the NIMH.