Gloria Patrick

Topographic quantitative EEG sequelae of chronic marihuana use: a replication using medically and psychiatrically screened normal subjects

In two previous studies it was reported that chronic marihuana (THC) use was associated with unique quantitative EEG features which were present in the non-intoxicated state. THC users, as contrasted with controls, had significant elevations of Absolute Power, Relative Power, and Coherence of alpha activity over the bilateral frontal cortex. Furthermore, a quantitative EEG discriminant function analyses permitted a 95% correct user versus non-user classification. However, because all of the THC users and 58% of the non-user controls were psychiatric inpatients, diagnostic and medication effects, if any, were uncontrolled. In the present study the same quantitative EEG methods were used to study daily THC users and non-user controls who underwent a rigorous screening process to insure that they were medically and psychiatrically healthy. The results of previous studies were replicated and an additional EEG correlate of chronic THC exposure (reduced alpha frequency) was identified.

Reduction of auditory P50 gating response in marihuana users: further supporting data.

This report attempts to replicate our recent finding of a significantly reduced sensory gating response in medically and psychiatrically normal chronic marihuana users. After exclusions, 10 normal heavy marihuana users (> or = 3 times per week) and 10 normal non-user controls were tested with the paired auditory P50 sensory gating procedure. Sensory gating ratios were significantly higher (i.e., impaired suppression) for THC users as compared to controls. Using combined data from the current and previous report, the degree of sensory gating impairment among THC users was significantly correlated with the frequency of marihuana use per week. Suggestions for further research are offered.

Topographic mapping of quantitative EEG variables in chronic heavy marihuana users: empirical findings with psychiatric patients.

EEG studies of marihuana use dating back to 1945 were reviewed. The earlier studies depended upon visual analysis of the tracing, and while some minor frequency and amplitude variations occurred in some subjects, there was no consistent THC induced change noticeable across subjects. Quantitative EEG studies of acute exposure to THC came later and produced reliable findings of a placebo controlled dose dependent THC induced increase in relative power of alpha, combined with decreased alpha frequency and a reduction of beta activity. These findings were reported for data collected from central-occipital derivations only. In our present investigation, we report that chronic heavy THC users have EEGs characterized by (1) increased absolute power of all frequencies over all cortical areas (2) hyperfrontality of elevated relative and absolute power and coherence values of alpha activity, and (3) a decrease in relative power of all non-alpha frequencies. Methodological issues were discussed and some suggestions were made for continuing research in this area.

Auditory and visual P300 event related potentials are not altered in medically and psychiatrically normal chronic marihuana users

Attempts to use Event Related Potentials, particularly the cognitive or P300 evoked potential, as measures of CNS effects of THC use have been infrequent and have produced inconsistent results. We published a pilot study in which psychiatric patient THC users had significantly prolonged auditory P300 latencies and reduced amplitudes as contrasted with non-users. Because psychiatric diagnoses and medication effects could not be controlled, we repeated the study with medically and psychiatrically normal subjects selected with extremely stringent exclusion criteria and screening procedures. P300 latency differences between THC users and controls were not detected. Using all subjects, THC users displayed reduced auditory and visual P300 amplitudes. However, when age differences between THC users and controls were removed, all significant P300 amplitude differences were removed as well. The contaminating effect of using psychiatric patients in THC research is discussed and the importance of using carefully screened normal subjects in studies of neurophysiological abuse drug effects is stressed.

Habituation and Motion Sickness

The vestibular, cerebellar, and reticular systems are central in importance, in motion sickness and habituation, to the effects of motion. Nuclear medicine single photon emission computed tomography (SPECT) studies of cerebral blood flow and power spectral electroencephalographic recordings during motion sickness were used to determine alterations in the central nervous system. The rotating chair with and without visual stimulation was used to study the rate of habituation and the effect of antimotion sickness medications on this rate. An increase of theta waves over the frontal cortex indicated a decreased activation of the higher centers during motion sickness. Motion sickness also produces an increase of blood flow in the central cerebellum that has connections to the reticular system. This increase in cerebellar activity is relayed to the reticular system whereby neural recruitment builds up to trigger the vomiting center, producing motion sickness. Habituation may be a conditioned compensatory activation of the reticular neurons that prevents this disruption of normal activation. The rate of habituation when motion sickness was prevented by scopolamine was slowed, indicating that, if the central nervous system is not challenged by disruption of normal activation, it does not produce the compensatory reactions that result in habituation.

Early and Middle Latency Evoked Potentials in Medically and Psychiatrically Normal Daily Marihuana Users: A Paucity of Significant Findings

The use of evoked potentials to study CNS effects of marihuana (THC) have produced inconsistent findings. Our previous pilot studies suggested that auditory P300 latencies and amplitudes, auditory P50 and somatosensory P30 amplitudes and brainstem auditory evoked potential latencies were altered in THC users. Because these findings were flawed by uncontrolled psychiatric diagnostic and medication variables, we undertook a controlled investigation of screened medically and psychiatrically normal THC users and controls. When age effects were controlled, THC related alterations of brain stem and both auditory and visual P300 responses could not be seen. This report extends our analyses to other auditory, somatosensory and visual evoked potentials. With the possible exception of an elevated auditory P50 amplitude, significant evoked potential correlates to daily THC use were not seen when normals were studied and age effects controlled.

Decreased multi-band posterior interhemispheric coherence with a lipoma on the corpus callosum: a case report of a possible association.

The corpus callosum plays a role in mediating interhemisphere communication. Coherence may be a quantitative EEG-based measure of this communication. The present report is of a female schizophrenic patient with a marked coherence deficit in the temporal-parietal-occipital region involving multiple frequency bands. An MRI scan of her brain revealed a lipoma involving the splenium of the corpus callosum. It is speculated that this lipoma may have caused a physical impingment on or developmental aberration of adjacent callosal fibers, resulting in the observed coherence deficit. Further studies of coherence measures in patients with collosal lipomas are proposed.

Topographic Quantitative EEG Measures of Alpha and Theta Power Changes during Caffeine Withdrawal: Preliminary Findings from Normal Subjects

Neurophysiological consequences of withdrawal from caffeine are poorly understood. In particular, quantitative studies of EEG changes that may occur during the period of caffeine abstinence in caffeine dependent individuals have not been reported. In this pilot study, 13 physically- and psychiatrically-normal caffeine users were asked to abstain from caffeine for a period of 4 days. Quantitative EEGs were obtained prior to stopping caffeine and on Days 1, 2, and 4 of the caffeine abstinence period. Results indicated that significant increases in alpha and theta absolute power accompany the caffeine withdrawal process with return to the pre-abstinent EEG levels when caffeine usage is resumed. The implications of these findings are discussed with special reference to the possible need to control for the variable of caffeine usage in quantitative EEG studies of other phenomena.

Acute Marihuana (THC) Exposure Produces a “Transient” Topographic Quantitative EEG Profile Identical to the “Persistent” Profile Seen in Chronic Heavy Users

In two published pilot studies and a controlled replication using screened normals, chronic marihuana (THC) use was associated with a unique topographic quantitative EEG profile, consisting of significant elevations of Absolute and Relative Power and Coherence of alpha activity over the bilateral frontal cortex as well as a significant decrease in alpha frequency. This report attempts to establish the causal influence of THC in the above findings by the transient production of this exact quantitative EEG profile in subjects who did not display it at the beginning. Using paced smoking of marihuana with high and low dose THC content and placebo marihuana in a counterbalanced design under double blind conditions, all four of the topographic features of chronic THC exposure were produced as transient effects by THC but not by placebo.

EEG does not predict response to valproate treatment of aggression in patients with borderline and antisocial personality disorders

Previous investigations of the role of EEG in predicting response of aggressive patients to valproate therapy have yielded mixed results. In this study of borderline and antisocial personality disorder patients hospitalized with aggressive behavior, EEGs were obtained prior to treatment with valproate. Eight of 22 (36.4%) patients subsequently responsive to valproate had nonepileptiform EEG abnormalities, while 5 of 20 (25%) patients not responsive to valproate had nonepileptiform EEG abnormalities. Although more of the valproate responders than nonresponders had EEG abnormalities, the presence of nonepileptiform EEG abnormalities was not a statistically significant (X2 = 0.213, df = 1, p = 0.64) predictor of valproate response in personality disorder patients with aggression.