RECENT PRESENTATIONS

Ilan, A.B., Nichols, E.A., Smith, M.E., Gevins, A. (2002). Acute Effects of Marijuana on Neurophysiological Signals of Memory and Focused Attention. Cognitive Neuroscience Society Ninth Annual Meeting. April, San Francisco.

ABSTRACT

The medial-prefrontal cortex and hippocampus are crucial for attentional control, working memory (WM), and the creation of more lasting memories. Acute marijuana usage often diminishes attention and memory capabilities, likely by altering the activity of CB1 cannabinoid receptors in these brain regions. To examine marijuana's effects on neurophysiological measures of WM, focused attention, and recent memory, a double-blind, counterbalanced study was performed in which 40-channel EEG recordings were obtained before and after 10 casual marijuana users smoked active or placebo marijuana. A spatial N-back task was used to measure WM and focused attention, and memory over a period of 5-10 minutes was measured with a word recognition task. Objective and subjective measures of intoxication increased after smoking marijuana, but alertness and motivation were unchanged. Marijuana smoking reduced EEG power in the theta band (4-6 Hz) but increased power in the alpha band (8-11 Hz), a signal inversely proportional to task-related cortical activation. Amplitudes of N1, P3, and slow wave event-related potentials (ERPs) decreased, also suggesting that marijuana smoking reduced the attentional resources allocated to task performance. In sum, marijuana slowed behavioral responses, altered neuronal synchronization in the cortex, and attenuated attention-related ERP amplitudes. Marijuana also appeared to hamper the ability to distinguish between words not recently seen and those presented 5 minutes earlier. Marijuana's impairment of attention and memory may result from alterations in the fine-tuning of synchronized, rhythmic neuronal populations in brain areas with dense concentrations of CB1 receptors. Supported by NIDA.