Original ArticlesReduced P50 auditory gating response in psychiatrically normal chronic marihuana users: a pilot study
Introduction
Our previous studies Struve et al 1989, Struve et al 1994, Struve et al 1995, Struve et al in submission have demonstrated and replicated a significant association between chronic marihuana (THC) use and topographic quantitative electroencephalographic (EEG) patterns of persistent “alpha hyperfrontality” (i.e., elevations of alpha absolute power, relative power, and interhemispheric coherence over frontal cortex) as well as reductions of alpha mean frequency. These findings from chronic users are consistent with both nontopographic Rodin et al 1970, Dornbush et al 1971, Dornbush et al 1972, Hockman et al 1971, Galanter et al 1973, Tassinari et al 1976, Volavka et al 1971, Volavka et al 1973, Volavka et al 1977 and topographic Manno et al 1993, Struve et al 1993, Struve et al 1996, Lukas et al 1995 transient EEG effects of acute THC administration; however, our attempts to demonstrate evoked potential sequelae of chronic marihuana use have been less successful. Although our initial pilot studies involving psychiatric patient chronic THC users and nonuser control subjects suggested that significant alterations of several evoked potential measures might be associated with chronic THC exposure (Straumanis et al 1991), subsequent work from our laboratory, using rigorously screened normal subjects Patrick and Struve 1994, Patrick et al 1995, Patrick et al 1997, failed to confirm these evoked potential findings.
This report presents pilot findings relating the P50 auditory sensory gating response to chronic cumulative THC exposure using a population of medically and psychiatrically screened normal subjects. In this evoked potential paradigm two auditory stimuli are presented very close together with the result that the amplitude of the second (“test”) stimulus evoked P50 wave is normally attenuated by the effects of the first (“conditioned”) stimulus (Davis et al 1966), a phenomenon first used by Adler et al (1982) to explore auditory evoked response differences between normal and clinical populations. The diminished P50 amplitude to the second stimulus constitutes sensory gating. A robust inhibitory gating mechanism can completely suppress the response to the test stimulus, whereas a total absence of gating would result in identical P50 amplitude response to both conditioning and test stimuli.
Section snippets
Subjects
The P50 sensory gating paradigm was introduced as a dependent measure late in an ongoing neurophysiological study of chronic THC exposure in normal subjects, and because of this, data were only available on a relatively small subsample of subjects still being entered into the parent project. Twenty-four chronic marihuana users and 19 nonuser control subjects were initially entered into a pilot P50 sensory gating study. Of these, data from 5 THC subjects and 5 control subjects had to be omitted
Results
Chronic THC use had no measurable effect on the P50 response to the first, or conditioning, click stimulus (THC group: mean latency = 56.7 msec, σ = 4.7 msec, range = 24 msec, control group: mean latency = 56.8 msec, σ = 4.9 msec, range = 20 msec, t = 0.028, df = 31, p = ns; mean amplitude: THC = 4.08 μV, control = 3.38 μV, t = 1.16, df = 31, p = ns). Thus both groups were found to be entirely comparable on the primary auditory P50 evoked response.
The distribution of auditory P50 gating ratios
Discussion
Evoked potential techniques have not been widely used to study the acute and chronic effects of THC exposure, and attempts to demonstrate changes in auditory, visual, and somatosensory early and middle latency evoked potentials have been variable, with no replicable findings clearly emerging Kopell et al 1978, Lewis et al 1973, Low et al 1973, Panayiotopoulos and Stefanis 1977, Rodin et al 1970, Roth et al 1973, Roth et al 1977, Straumanis et al 1991, Tassinari et al 1974, Tinklenberg 1972.
Acknowledgements
Supported in part by NIDA grant DA06643.
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2013, International Journal of PsychophysiologyCitation Excerpt :A small body of research has examined P50 sensory gating in cannabis users. This work has reported reduced P50 suppression in chronic cannabis users compared to non-user controls (Edwards et al., 2009; Patrick et al., 1999; Patrick and Struve, 2000, 2002; Rentzsch et al., 2007), and interestingly in comparison to patients with schizophrenia with and without concurrent cannabis use (Rentzsch et al., 2007). Some of these studies found that poor sensory gating in cannabis users is associated with prolonged durations of exposure (Rentzsch et al., 2007) and dose (the number of joints smoked in the previous six months, Edwards et al., 2009).