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PhD Thesis - Solowij, N

Event-related potential indices of cognitive functioning in long term cannabis users
Nadia Solowij (1995)

Abstract:
This thesis investigates cognitive impairments associated with chronic use of cannabis in a series of brain event-related potential (ERP) studies of selective attention. The first experiment found few differences between users and controls in a simple auditory discrimination paradigm. In experiment two, a complex auditory selective attention task showed that users differed significantly from controls in efficiency of information processing. Subjects attended to tones that varied in location, pitch and duration and responded to long duration tones of a particular location and pitch. Cannabis users' task performance was poorer than that of controls and users showed enhanced early processing negativity (PN) to stimuli of irrelevant pitch in the attended ear. This indicates that users engaged in unnecessary pitch processing and had difficulty in filtering out irrelevant information. P300 was reduced in the user group, suggesting a dysfunction in the allocation of attentional resources and stimulus evaluation strategies. Experiment three replicated the finding of large PN to pitch irrelevant stimuli in a larger sample, and examined the effects of frequency and duration of cannabis use. The ability to focus attention and reject irrelevant information, measured by PN to irrelevant stimuli, was progressively impaired with the number of years of use but was unrelated to frequency of use. The speed of information processing, measured by P300 latency, was significantly delayed with increasing frequency of use but was unrelated to duration of use. These results suggest that a chronic build up of cannabinoids produces both short and long term cognitive impairments. Experiment four assessed the reversibility of the PN effect in ex-cannabis users. The results showed that the large PN to irrelevant stimuli partially resolved following cessation of cannabis use. There was still a significant relationship between PN and past duration of cannabis use, and ex-users' task performance was poorer than that of controls. This suggests that past exposure to cannabis continues to affect electrophysiology and cognition well after discontinuing use. The conclusion from this research is that long term cannabis use progressively impairs the ability to process information efficiently, and there is only partial recovery with cessation of use.

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