Cannabinoid modulations of resting state EEG θ power and working memory are correlated in humans

Chronic cannabis use alters the spontaneous and oscillatory gamma dynamics serving cognitive control

Regular cannabis use is associated with cortex-wide changes in spontaneous and oscillatory activity, although the functional significance of such changes remains unclear. We hypothesized that regular cannabis use would suppress spontaneous gamma activity in regions serving cognitive control and scale with task performance. Participants (34 cannabis users, 33 nonusers) underwent an interview regarding their substance use history and completed the Eriksen flanker task during magnetoencephalography (MEG). MEG data were imaged in the time-frequency domain and virtual sensors were extracted from the peak voxels of the grand-averaged oscillatory interference maps to quantify spontaneous gamma activity during the pre-stimulus baseline period. We then assessed group-level differences in spontaneous and oscillatory gamma activity, and their relationship with task performance and cannabis use metrics. Both groups exhibited a significant behavioral flanker interference effect, with slower responses during incongruent relative to congruent trials. Mixed-model ANOVAs indicated significant gamma-frequency neural interference effects in the left frontal eye fields (FEF) and left temporoparietal junction (TPJ). Further, a group-by-condition interaction was detected in the left FEF, with nonusers exhibiting stronger gamma oscillations during incongruent relative to congruent trials and cannabis users showing no difference. In addition, spontaneous gamma activity was sharply suppressed in cannabis users relative to nonusers in the left FEF and TPJ. Finally, spontaneous gamma activity in the left FEF and TPJ was associated with task performance across all participants, and greater cannabis use was associated with weaker spontaneous gamma activity in the left TPJ of the cannabis users. Regular cannabis use was associated with weaker spontaneous gamma in the TPJ and FEF. Further, the degree of use may be proportionally related to the degree of suppression in spontaneous activity in the left TPJ.

Regular recreational Cannabis users exhibit altered neural oscillatory dynamics during attention reorientation

BACKGROUND

Cannabis is the most widely used illicit drug in the United States and is often associated with changes in attention function, which may ultimately impact numerous other cognitive faculties (e.g. memory, executive function). Importantly, despite the increasing rates of cannabis use and widespread legalization in the United States, the neural mechanisms underlying attentional dysfunction in chronic users are poorly understood.

METHODS

We used magnetoencephalography (MEG) and a modified Posner cueing task in 21 regular cannabis users and 32 demographically matched non-user controls. MEG data were imaged in the time-frequency domain using a beamformer and peak voxel time series were extracted to quantify the oscillatory dynamics underlying use-related aberrations in attentional reorienting, as well as the impact on spontaneous neural activity immediately preceding stimulus onset.

RESULTS

Behavioral performance on the task (e.g. reaction time) was similar between regular cannabis users and non-user controls. However, the neural data indicated robust theta-band synchronizations across a distributed network during attentional reorienting, with activity in the bilateral inferior frontal gyri being markedly stronger in users relative to controls (p's < 0.036). Additionally, we observed significantly reduced spontaneous theta activity across this distributed network during the pre-stimulus baseline in cannabis users relative to controls (p's < 0.020).

CONCLUSIONS

Despite similar performance on the task, we observed specific alterations in the neural dynamics serving attentional reorienting in regular cannabis users compared to controls. These data suggest that regular cannabis users may employ compensatory processing in the prefrontal cortices to efficiently reorient their attention relative to non-user controls.

The Relationship Between Cannabinoids and Neural Oscillations: How Cannabis Disrupts Sensation, Perception, and Cognition

Disruptions in neural oscillations are believed to be one critical mechanism by which cannabinoids, such as delta-9-tetrahyrdrocannabinol (THC; the primary psychoactive constituent of cannabis), perturbs brain function. Here we briefly review the role of synchronized neural activity, particularly in the gamma (30-80 Hz) and theta (4-7 Hz) frequency range, in sensation, perception, and cognition. This is followed by a review of clinical studies utilizing electroencephalography (EEG) which have demonstrated that both chronic and acute cannabinoid exposure disrupts neural oscillations in humans. We also offer a hypothetical framework through which endocannabinoids modulate neural synchrony at the network level. This also includes speculation on how both chronic and acute cannabinoids disrupt functionally relevant neural oscillations by altering the fine tuning of oscillations and the inhibitory/excitatory balance of neural circuits. Finally, we highlight important clinical implications of such oscillatory disruptions, such as the potential relationship between cannabis use, altered neural synchrony, and disruptions in sensation, perception, and cognition, which are perturbed in disorders such as schizophrenia.

Adolescents are more sensitive than adults to acute behavioral and cognitive effects of THC

Increased cannabis availability has contributed to increased use with concomitant incidence of adverse effects. One risk factor for adverse drug reactions may be age. There is preclinical evidence that acute effects of delta-9-tetrahydrocannabinol (THC), the primary active constituent of cannabis, are greater during adolescence, but this has not been fully studied in humans. The present study sought to determine whether adolescent men and women are more sensitive than adults to acute THC. Adolescents aged 18-20 (N = 12) and adults aged 30-40 (N = 12), with less than 20 total lifetime uses of THC-containing products, received capsules of THC (7.5, 15 mg) and placebo across three study sessions in randomized order under double blind conditions. During each session, subjective, cardiovascular, behavioral, and EEG measures were obtained. Behavioral measures included Simple Reaction Time, Stop Task, Time Production and N-back and EEG measures included P300 amplitudes during an auditory oddball task and eyes-closed resting state. THC affected subjective state and heart rate similarly in both age groups. However, adolescents were more sensitive to performance impairing effects, exhibiting dose-dependent impairments on reaction time, response accuracy, and time perception. On EEG measures, THC dose-dependently decreased P300 amplitude in adolescents but not adults. Adolescents were more sensitive to behavioral and cognitive effects of THC, but not to cardiovascular effects or subjective measures. Thus, at doses that produce comparable ratings of intoxication, adolescents may exhibit greater cognitive impairment and alterations in brain function.

The Construct of Medical and Non-Medical Marijuana—Critical Review

The rising popularity of medical marijuana and its potential therapeutic uses has resulted in passionate discussions that have mainly focused on its possible benefits and applications. Although the concept itself seems promising, the multitude of presented information has noticeable ramifications—terminological chaos being one. This work aimed to synthesize and critically analyze scientific evidence on the therapeutic uses of cannabinoids in the field of psychiatry. Emphasis was placed on the anxiolytic effects of cannabis constituents and their effects on post-traumatic stress disorder, anxiety disorders, schizophrenia spectrum, and other psychotic disorders. The review was carried out from an addictological perspective. A database search of interchangeably combined keywords resulted in the identification of subject-related records. The data were then analyzed in terms of relevance, contents, methodologies, and cited papers. The results were clear in supporting one common conclusion: while most findings provide support for beneficial applications of medical marijuana in psychiatry, no certain conclusions can be drawn until larger-scaled, more methodologically rigorous, and (preferably) controlled randomized trials verify these discoveries.

Theta and Alpha Oscillatory Activity During Working Memory Maintenance in Long-Term Cannabis Users: The Importance of the Polydrug Use Context

Background: Impairments in various subdomains of memory have been associated with chronic cannabis use, but less is known about their neural underpinnings, especially in the domain of the brain's oscillatory activity. Aims: To investigate neural oscillatory activity supporting working memory (WM) in regular cannabis users and non-using controls. We focused our analyses on frontal midline theta and posterior alpha asymmetry as oscillatory fingerprints for the WM's maintenance process. Methods: 30 non-using controls (CG) and 57 regular cannabis users-27 exclusive cannabis users (CU) and 30 polydrug cannabis users (PU) completed a Sternberg modified WM task with a concurrent electroencephalography recording. Theta, alpha and beta frequency bands were examined during WM maintenance. Results: When compared to non-using controls, the PU group displayed increased frontal midline theta (FMT) power during WM maintenance, which was positively correlated with RT. The posterior alpha asymmetry during the maintenance phase, on the other hand, was negatively correlated with RT in the CU group. WM performance did not differ between groups. Conclusions: Both groups of cannabis users (CU and PU), when compared to the control group, displayed differences in oscillatory activity during WM maintenance, unique for each group (in CU posterior alpha and in PU FMT correlated with performance). We interpret those differences as a reflection of compensatory strategies, as there were no differences between groups in task performance. Understanding the psychophysiological processes in regular cannabis users may provide insight on how chronic use may affect neural networks underlying cognitive processes, however, a polydrug use context (i.e., combining cannabis with other illegal substances) seems to be an important factor.

Alterations in Electroencephalography Theta as Candidate Biomarkers of Acute Cannabis Intoxication

The trend toward cannabis legalization in the United States over the past two decades has unsurprisingly been accompanied by an increase in the number of cannabis users and use patterns that potentially pose wider risks to the public like driving under the influence. As such, it is becoming increasingly important to develop methods to accurately quantify cannabis intoxication and its associated impairments on cognitive and motor function. Electroencephalography (EEG) offers a non-invasive method for quantitatively assessing neurophysiological biomarkers of intoxication and impairment with a high degree of temporal resolution. Twelve healthy, young recreational cannabis users completed a series of neurocognitive tasks with concurrent EEG acquisition using the ABM STAT X24 EEG headset in a within-subject counterbalanced design. The 1-h testbed consisted of resting state tasks and tests of attention and memory. Spectral densities were computed for resting state tasks, and event-related potentials (ERPs) were obtained for the attention and memory tasks. Theta band power (3–5 Hz) was decreased during cannabis intoxication compared to placebo during resting state tasks, as were average P400 and late positive potential (LPP) amplitudes during attention and memory tasks. Cannabis intoxication was also associated with elevated frontal coherence and diminished anterior–posterior coherence in the Theta frequency band. This work highlights the utility of EEG to identify and quantify neurophysiological biomarkers from recordings obtained during a short neurocognitive testbed as a method for profiling cannabis intoxication. These biomarkers may prove efficacious in distinguishing intoxicated from non-intoxicated individuals in lab and real-world settings.

Dynamics of the accommodative response after smoking cannabis

PURPOSE

Cannabis is the most widely consumed illicit drug worldwide. It has been suggested that cannabis could generate blurred vision during reading tasks. The goal of this study was to objectively assess the acute effects of smoking cannabis on the dynamics of ocular accommodation. The influence of other factors, including target distance and the direction of accommodation, as well as personal characteristics, were also analysed.

METHODS

Nineteen young people who were occasional cannabis users participated in the study (mean age 22.53 [3.12] years). Their usage profiles were evaluated by means of the Cannabis Use Disorders Identification Test-revised (CUDIT-r). The dynamics of the accommodative response were evaluated using an open-field auto refractor (Grand Seiko WAM-5500). The participants completed two different experimental sessions, one week apart, and in random order (baseline session and after smoking cannabis). During these sessions, the amplitude of the response (D), mean velocity (D/s), peak velocity (D/s), response time (s), accommodative lag (D) and accommodation variability (D) were measured.

RESULTS

The results indicated that cannabis use had a significant main effect on the mean accommodation/disaccommodation velocity (F_1,13  = 7.21; p = 0.02; η p 2  = 0.396). Cannabis consumption also interacted significantly with other factors. Response time showed a significant two-way interaction between condition × target distance (F_1,13  = 11.71; p = 0.005; η p 2  = 0.474) and condition × accommodation direction (F_1,13  = 8.71; p = 0.01; η p 2  = 0.401). For mean velocity, two-way interactions were found between condition × age (F_1,13  = 6.03; p = 0.03; η p 2  = 0.354), condition × CUDIT-r score (F_1,13  = 6.03; p = 0.03; η p 2  = 0.356) and condition × target distance (F_1,13  = 7.20; p = 0.02; η p 2  = 0.396).

CONCLUSIONS

These findings suggest that cannabis use can alter the accommodation process, although further studies should be carried out to explore the role of attention deficits. According to these results, certain daily activities that depend on an accurate accommodative function may be affected by cannabis use.

Effects of Cannabis Consumption on Sleep

Despite the fact that medical properties of Cannabis have been recognized for more than 5000 years, the use of Cannabis for medical purposes have recently reemerged and became more accessible. Cannabis is usually employed as a self-medication for the treatment of insomnia disorder. However, the effects of Cannabis on sleep depend on multiple factors such as metabolomic composition of the plant, dosage and route of administration. In the present chapter, we reviewed the main effect Cannabis on sleep. We focused on the effect of "crude or whole plant" Cannabis consumption (i.e., smoked, oral or vaporized) both in humans and experimental animal models.The data reviewed establish that Cannabis modifies sleep. Furthermore, a recent experimental study in animals suggests that vaporization (which is a recommended route for medical purposes) of Cannabis with high THC and negligible CBD, promotes NREM sleep. However, it is imperative to perform new clinical studies in order to confirm if the administration of Cannabis could be a beneficial therapy for the treatment of sleep disorders.

Vulnerability to addiction

Addiction is a chronic brain disease that has dramatic health and socioeconomic consequences worldwide. Multiple approaches have been used for decades to clarify the neurobiological basis of this disease and to identify novel potential treatments. This review summarizes the main brain networks involved in the vulnerability to addiction and specific innovative technological approaches to investigate these neural circuits. First, the evolution of the definition of addiction across the Diagnostic and Statistical Manual of Mental Disorders (DSM) is revised. We next discuss several innovative experimental techniques that, combined with behavioral approaches, have allowed recent critical advances in understanding the neural circuits involved in addiction, including DREADDs, calcium imaging, and electrophysiology. All these techniques have been used to investigate specific neural circuits involved in vulnerability to addiction and have been extremely useful to clarify the neurobiological basis of each specific component of the addictive process. These novel tools targeting specific brain regions are of great interest to further understand the different aspects of this complex disease. This article is part of the special issue on 'Vulnerabilities to Substance Abuse.'.

Acute effects of partial CB1 receptor agonists on cognition - A meta-analysis of human studies

BACKGROUND

Impairment in cognition is frequently associated with acute cannabis consumption. However, some questions remain unanswered as to which deficits are most prominent and which demographic groups are most vulnerable.

METHODS

A literature search yielded 52 experimental studies of acute administration of partial CB₁ receptor agonists (i.e. cannabis, THC, and nabilone) that assessed cognitive dysfunction in 1580 healthy volunteers. Effect size estimates were calculated using the Comprehensive Meta-Analysis for the following six cognitive domains: attention, executive functions, impulsivity, speed of processing, verbal learning/memory, and working memory.

RESULTS

There were small-to-moderate impairments across all cognitive domains. Deficits in verbal learning/memory and working memory were more prominent, whereas attention and impulsivity were the least affected. Meta-regression analysis revealed that the greater the male ratio is in a sample, the greater the negative effect of cannabinoids on speed of processing and impulsivity. Analysis of route of administration showed that the deficits in speed of processing were smaller in the oral, relative to smoking, vaping, and intravenous administration studies. A publication bias was observed.

DISCUSSION

Verbal learning/memory and working memory are most prominently affected by acute administration of partial CB₁ receptor agonists. The results are consistent with the residual cognitive effects that have been documented among chronic cannabis users.

Investigation of Safety and Tolerability of ASP3652 Based on Clinical Studies of Cerebrospinal Fluid Transfer After Multiple Doses and Exposure After Single Doses at High Dose Levels

INTRODUCTION

The studies described here were conducted to investigate the central nervous system (CNS) transfer of ASP3652, a peripherally acting inhibitor of fatty acid amide hydrolase, after multiple doses at around the anticipated therapeutic dose and the safety, tolerability, and pharmacokinetics after single doses at corresponding supratherapeutic doses in healthy subjects.

METHODS

Study 1 was an open-label multiple dose study in which ASP3652 (300 mg bid) or matching placebo was administered in multiple doses to healthy subjects. Study 2 was a placebo-controlled, randomized 4 × 4 crossover study in which ASP3652 was given as three single ascending doses of ASP3652 (600-1800 mg) or matching placebo to healthy subjects. Levels of ASP3652 and endocannabinoids (eCBs) in plasma, cerebrospinal fluid (CSF) (study 1 only), and safety were evaluated.

RESULTS

In study 1, ASP3652 was readily absorbed to reach C_max at 1 h after dosing. AUC_tau and C_max of ASP3652 in CSF were approximately 0.2% and 0.06% of the AUC_tau and C_max in plasma after multiple doses of ASP3652 300 mg bid. At steady state the area under the response-time curve (AURC) from 0 to 12 h and the maximum response for anandamide in plasma were approximately 550-fold and 230-fold higher than those in CSF. In study 2, the C_max and AUC of ASP3652 increased higher than dose proportionally in subjects receiving 600-1800 mg ASP3652. For eCBs, although the AURC increased less than dose proportionally, maximum plasma levels were comparable across all treatment groups. The incidence of adverse events (AEs) was similar across all treatment groups including the placebo group. There was no evidence of CNS-related side effects.

CONCLUSIONS

ASP3652 showed low CNS penetration at the anticipated therapeutic dose and was well tolerable without any CNS-related AEs at supratherapeutic doses, supporting that the drug can be safely tested at the anticipated therapeutic dose.

TRIAL REGISTRATION

ClinicalTrials.gov identifier, NCT02034734 for study 1, NCT01815684 for study 2.

The neuropsychopharmacology of cannabis: A review of human imaging studies

The laws governing cannabis are evolving worldwide and associated with changing patterns of use. The main psychoactive drug in cannabis is Δ⁹-tetrahydrocannabinol (THC), a partial agonist at the endocannabinoid CB₁ receptor. Acutely, cannabis and THC produce a range of effects on several neurocognitive and pharmacological systems. These include effects on executive, emotional, reward and memory processing via direct interactions with the endocannabinoid system and indirect effects on the glutamatergic, GABAergic and dopaminergic systems. Cannabidiol, a non-intoxicating cannabinoid found in some forms of cannabis, may offset some of these acute effects. Heavy repeated cannabis use, particularly during adolescence, has been associated with adverse effects on these systems, which increase the risk of mental illnesses including addiction and psychosis. Here, we provide a comprehensive state of the art review on the acute and chronic neuropsychopharmacology of cannabis by synthesizing the available neuroimaging research in humans. We describe the effects of drug exposure during development, implications for understanding psychosis and cannabis use disorder, and methodological considerations. Greater understanding of the precise mechanisms underlying the effects of cannabis may also give rise to new treatment targets.

Cannabis users exhibit increased cortical activation during resting state compared to non-users

Studies have shown altered task-based brain functioning as a result of cannabis use. To date, however, whether similar alterations in baseline resting state and functional organization of neural activity are observable in cannabis users remains unknown. We characterized global resting state cortical activations and functional connectivity via electroencephalography (EEG) in cannabis users and related these activations to measures of cannabis use. Resting state EEG in the eyes closed condition was collected from age- and sex-matched cannabis users (N = 17; 6 females; mean age = 30.9 ± 7.4 years) and non-using controls (N = 21; 9 females; mean age = 33.1 ± 11.6 years). Power spectral density and spectral coherence were computed to determine differences in cortical activations and connectivity between the two groups in the delta (1-4Hz), theta (4-7 Hz), alpha (8-12 Hz), beta (13-30 Hz), and gamma (31-50 Hz) frequency bands. Cannabis users exhibited decreased delta and increased theta, beta, and gamma power compared to controls, suggesting increased cortical activation in resting state and a disinhibition of inhibitory functions that may interrupt cognitive processes. Cannabis users also exhibited increased interhemispheric and intrahemispheric coherence relative to controls, reduced mean network degree, and increased clustering coefficient in specific regions and frequencies. This increased cortical activity may indicate a loss of neural refinement and efficiency that may indicate a "noisy" brain. Lastly, measures related to cannabis use were correlated with spectral power and functional connectivity measures, indicating that specific electrophysiological signals are associated with cannabis use. These results suggest that there are differences in cortical activity and connectivity between cannabis users and non-using controls in the resting state that may be related to putative cognitive impairments and can inform effectiveness of intervention programs.

Practice effects in nutrition intervention studies with repeated cognitive testing

BACKGROUND:

There is growing interest in the use of nutrition interventions to improve cognitive function. To determine intervention efficacy, repeated cognitive testing is often required. However, performance on tasks can improve through practice, irrespective of any intervention.

OBJECTIVE:

This study investigated practice effects for commonly used cognitive tasks (immediate and delayed recall, serial subtractions, Stroop and the Sternberg task) to identify appropriate methodology for minimising their impact on nutrition intervention outcomes.

METHODS:

Twenty-nine healthy young adults completed six repetitions of the cognitive battery (two sessions on each of three separate visits). Subjective measures of mood, motivation and task difficulty were also recorded at each repetition.

RESULTS:

Significant practice effects were apparent for all tasks investigated and were attenuated, but not fully eliminated, at later visits compared with the earlier visits. Motivation predicted cognitive performance for the tasks rated most difficult by participants (serial 7s, immediate and delayed recall). While increases in mental fatigue and corresponding decreases in positive mood were observed between test sessions occurring on the same day, there were no negative consequences of long term testing on mood across the duration of the study.

CONCLUSION:

Practice effects were evident for all investigated cognitive tasks, with strongest effects apparent between visits one and two. Methodological recommendations to reduce the impact of practice on the statistical power of future intervention studies have been made, including the use of alternate task forms at each repetition and the provision of a familiarisation visit on a separate day prior to data collection.

Cannabinoid receptor-mediated disruption of sensory gating and neural oscillations: A translational study in rats and humans

Cannabis use has been associated with altered sensory gating and neural oscillations. However, it is unclear which constituent in cannabis is responsible for these effects, or whether these are cannabinoid receptor 1 (CB1R) mediated. Therefore, the present study in humans and rats examined whether cannabinoid administration would disrupt sensory gating and evoked oscillations utilizing electroencephalography (EEG) and local field potentials (LFPs), respectively. Human subjects (n = 15) completed four test days during which they received intravenous delta-9-tetrahydrocannabinol (Δ⁹-THC), cannabidiol (CBD), Δ⁹-THC + CBD, or placebo. Subjects engaged in a dual-click paradigm, and outcome measures included P50 gating ratio (S2/S1) and evoked power to S1 and S2. In order to examine CB1R specificity, rats (n = 6) were administered the CB1R agonist CP-55940, CP-55940+AM-251 (a CB1R antagonist), or vehicle using the same paradigm. LFPs were recorded from CA3 and entorhinal cortex. Both Δ⁹-THC (p < 0.007) and Δ⁹-THC + CBD (p < 0.004) disrupted P50 gating ratio compared to placebo, while CBD alone had no effect. Δ⁹-THC (p < 0.048) and Δ⁹-THC + CBD (p < 0.035) decreased S1 evoked theta power, and in the Δ⁹-THC condition, S1 theta negatively correlated with gating ratios (r = -0.629, p < 0.012 (p < 0.048 adjusted)). In rats, CP-55940 disrupted gating in both brain regions (p < 0.0001), and this was reversed by AM-251. Further, CP-55940 decreased evoked theta (p < 0.0077) and gamma (p < 0.011) power to S1, which was partially blocked by AM-251. These convergent human/animal data suggest that CB1R agonists disrupt sensory gating by altering neural oscillations in the theta-band. Moreover, this suggests that the endocannabinoid system mediates theta oscillations relevant to perception and cognition.

Cannabinoids and Vanilloids in Schizophrenia: Neurophysiological Evidence and Directions for Basic Research

Much of our knowledge of the endocannabinoid system in schizophrenia comes from behavioral measures in rodents, like prepulse inhibition of the acoustic startle and open-field locomotion, which are commonly used along with neurochemical approaches or drug challenge designs. Such methods continue to map fundamental mechanisms of sensorimotor gating, hyperlocomotion, social interaction, and underlying monoaminergic, glutamatergic, and GABAergic disturbances. These strategies will require, however, a greater use of neurophysiological tools to better inform clinical research. In this sense, electrophysiology and viral vector-based circuit dissection, like optogenetics, can further elucidate how exogenous cannabinoids worsen (e.g., tetrahydrocannabinol, THC) or ameliorate (e.g., cannabidiol, CBD) schizophrenia symptoms, like hallucinations, delusions, and cognitive deficits. Also, recent studies point to a complex endocannabinoid-endovanilloid interplay, including the influence of anandamide (endogenous CB₁ and TRPV₁ agonist) on cognitive variables, such as aversive memory extinction. In fact, growing interest has been devoted to TRPV₁ receptors as promising therapeutic targets. Here, these issues are reviewed with an emphasis on the neurophysiological evidence. First, we contextualize imaging and electrographic findings in humans. Then, we present a comprehensive review on rodent electrophysiology. Finally, we discuss how basic research will benefit from further combining psychopharmacological and neurophysiological tools.

Cannabis-associated psychosis: Neural substrate and clinical impact

Prospective epidemiological studies have consistently demonstrated that cannabis use is associated with an increased subsequent risk of both psychotic symptoms and schizophrenia-like psychoses. Early onset of use, daily use of high-potency cannabis, and synthetic cannabinoids carry the greatest risk. The risk-increasing effects are not explained by shared genetic predisposition between schizophrenia and cannabis use. Experimental studies in healthy humans show that cannabis and its active ingredient, delta-9-tetrahydrocannabinol (THC), can produce transient, dose-dependent, psychotic symptoms, as well as an array of psychosis-relevant behavioral, cognitive and psychophysiological effects; the psychotogenic effects can be ameliorated by cannabidiol (CBD). Findings from structural imaging studies in cannabis users have been inconsistent but functional MRI studies have linked the psychotomimetic and cognitive effects of THC to activation in brain regions implicated in psychosis. Human PET studies have shown that acute administration of THC weakly releases dopamine in the striatum but that chronic users are characterised by low striatal dopamine. We are beginning to understand how cannabis use impacts on the endocannabinoid system but there is much still to learn about the biological mechanisms underlying how cannabis increases risk of psychosis. This article is part of the Special Issue entitled "A New Dawn in Cannabinoid Neurobiology".

Human Laboratory Studies on Cannabinoids and Psychosis

Some of the most compelling evidence supporting an association between cannabinoid agonists and psychosis comes from controlled laboratory studies in humans. Randomized, double-blind, placebo-controlled, crossover laboratory studies demonstrate that cannabinoid agonists, including phytocannabinoids and synthetic cannabinoids, produce a wide range of positive, negative, and cognitive symptoms and psychophysiologic deficits in healthy human subjects that resemble the phenomenology of schizophrenia. These effects are time locked to drug administration, are dose related, and are transient and rarely necessitate intervention. The magnitude of effects is similar to the effects of ketamine but qualitatively distinct from other psychotomimetic drugs, including ketamine, amphetamine, and salvinorin A. Cannabinoid agonists have also been shown to transiently exacerbate symptoms in individuals with schizophrenia in laboratory studies. Patients with schizophrenia are more vulnerable than healthy control subjects to the acute behavioral and cognitive effects of cannabinoid agonists and experience transient exacerbation of symptoms despite treatment with antipsychotic medications. Furthermore, laboratory studies have failed to demonstrate any "beneficial" effects of cannabinoid agonists in individuals with schizophrenia-challenging the cannabis self-medication hypothesis. Emerging evidence suggests that polymorphisms of several genes related to dopamine metabolism (e.g., COMT, DAT1, and AKT1) may moderate the effects of cannabinoid agonists in laboratory studies. Cannabinoid agonists induce dopamine release, although the magnitude of release does not appear to be commensurate to the magnitude and spectrum of their acute psychotomimetic effects. Interactions between the endocannabinoid, gamma-aminobutyric acid, and glutamate systems and their individual and interactive effects on neural oscillations provide a plausible mechanism underlying the psychotomimetic effects of cannabinoids.

It's All in the Rhythm: The Role of Cannabinoids in Neural Oscillations and Psychosis

Evidence has accumulated over the past several decades suggesting that both exocannabinoids and endocannabinoids play a role in the pathophysiology of schizophrenia. The current article presents evidence suggesting that one of the mechanisms whereby cannabinoids induce psychosis is through the alteration in synchronized neural oscillations. Neural oscillations, particularly in the gamma (30-80 Hz) and theta (4-7 Hz) ranges, are disrupted in schizophrenia and are involved in various areas of perceptual and cognitive function. Regarding cannabinoids, preclinical evidence from slice and local field potential recordings has shown that central cannabinoid receptor (cannabinoid receptor type 1) agonists decrease the power of neural oscillations, particularly in the gamma and theta bands. Further, the administration of cannabinoids during critical stages of neural development has been shown to disrupt the brain's ability to generate synchronized neural oscillations in adulthood. In humans, studies examining the effects of chronic cannabis use (utilizing electroencephalography) have shown abnormalities in neural oscillations in a pattern similar to those observed in schizophrenia. Finally, recent studies in humans have also shown disruptions in neural oscillations after the acute administration of delta-9-tetrahydrocannabinol, the primary psychoactive constituent in cannabis. Taken together, these data suggest that both acute and chronic cannabinoids can disrupt the ability of the brain to generate synchronized oscillations at functionally relevant frequencies. Hence, this may represent one of the primary mechanisms whereby cannabinoids induce disruptions in attention, working memory, sensory-motor integration, and many other psychosis-related behavioral effects.

Distinguishing cognitive state with multifractal complexity of hippocampal interspike interval sequences

Fractality, represented as self-similar repeating patterns, is ubiquitous in nature and the brain. Dynamic patterns of hippocampal spike trains are known to exhibit multifractal properties during working memory processing; however, it is unclear whether the multifractal properties inherent to hippocampal spike trains reflect active cognitive processing. To examine this possibility, hippocampal neuronal ensembles were recorded from rats before, during and after a spatial working memory task following administration of tetrahydrocannabinol (THC), a memory-impairing component of cannabis. Multifractal detrended fluctuation analysis was performed on hippocampal interspike interval sequences to determine characteristics of monofractal long-range temporal correlations (LRTCs), quantified by the Hurst exponent, and the degree/magnitude of multifractal complexity, quantified by the width of the singularity spectrum. Our results demonstrate that multifractal firing patterns of hippocampal spike trains are a marker of functional memory processing, as they are more complex during the working memory task and significantly reduced following administration of memory impairing THC doses. Conversely, LRTCs are largest during resting state recordings, therefore reflecting different information compared to multifractality. In order to deepen conceptual understanding of multifractal complexity and LRTCs, these measures were compared to classical methods using hippocampal frequency content and firing variability measures. These results showed that LRTCs, multifractality, and theta rhythm represent independent processes, while delta rhythm correlated with multifractality. Taken together, these results provide a novel perspective on memory function by demonstrating that the multifractal nature of spike trains reflects hippocampal microcircuit activity that can be used to detect and quantify cognitive, physiological, and pathological states.

Weeding out bad waves: towards selective cannabinoid circuit control in epilepsy

Endocannabinoids are lipid-derived messengers, and both their synthesis and breakdown are under tight spatiotemporal regulation. As retrograde signalling molecules, endocannabinoids are synthesized postsynaptically but activate presynaptic cannabinoid receptor 1 (CB1) receptors to inhibit neurotransmitter release. In turn, CB1-expressing inhibitory and excitatory synapses act as strategically placed control points for activity-dependent regulation of dynamically changing normal and pathological oscillatory network activity. Here, we highlight emerging principles of cannabinoid circuit control and plasticity, and discuss their relevance for epilepsy and related comorbidities. New insights into cannabinoid signalling may facilitate the translation of the recent interest in cannabis-related substances as antiseizure medications to evidence-based treatment strategies.

Delta-9-tetrahydrocannabinol, neural oscillations above 20 Hz and induced acute psychosis

RATIONALE

An acute challenge with delta-9-tetrahydrocannabinol (THC) can induce psychotic symptoms including delusions. High electroencephalography (EEG) frequencies, above 20 Hz, have previously been implicated in psychosis and schizophrenia.

OBJECTIVES

The objective of this study is to determine the effect of intravenous THC compared to placebo on high-frequency EEG.

METHODS

A double-blind cross-over study design was used. In the resting state, the high-beta to low-gamma magnitude (21-45 Hz) was investigated (n = 13 pairs + 4 THC only). Also, the event-related synchronisation (ERS) of motor-associated high gamma was studied using a self-paced button press task (n = 15).

RESULTS

In the resting state, there was a significant condition × frequency interaction (p = 0.00017), consisting of a shift towards higher frequencies under THC conditions (reduced high beta [21-27 Hz] and increased low gamma [27-45 Hz]). There was also a condition × frequency × location interaction (p = 0.006), such that the reduction in 21-27-Hz magnitude tended to be more prominent in anterior regions, whilst posterior areas tended to show greater 27-45-Hz increases. This effect was correlated with positive symptoms, as assessed on the Positive and Negative Syndrome Scale (PANSS) (r = 0.429, p = 0.042). In the motor task, there was a main effect of THC to increase 65-130-Hz ERS (p = 0.035) over contra-lateral sensorimotor areas, which was driven by increased magnitude in the higher, 85-130-Hz band (p = 0.02) and not the 65-85-Hz band.

CONCLUSIONS

The THC-induced shift to faster gamma oscillations may represent an over-activation of the cortex, possibly related to saliency misattribution in the delusional state.

Genetic variability in the human cannabinoid receptor 1 is associated with resting state EEG theta power in humans

It has long been postulated that exogenous cannabinoids have a profound effect on human cognitive functioning. These cannabinoid effects are thought to depend, at least in parts, on alterations of phase-locking of local field potential neuronal firing. The latter can be measured as activity in the theta frequency band (4-7Hz) by electroencephalogram. Theta oscillations are supposed to serve as a mechanism in neural representations of behaviorally relevant information. However, it remains unknown whether variability in endogenous cannabinoid activity is involved in theta rhythms and therefore, may serve as an individual differences index of human cognitive functioning. To clarify this issue, we recorded resting state EEG activity in 164 healthy human subjects and extracted EEG power across frequency bands (δ, θ, α, and β). To assess variability in the endocannabinoid system, two genetic polymorphisms (rs1049353, rs2180619) within the cannabinoid receptor 1 (CB1) were determined in all participants. As expected, we observed significant effects of rs1049353 on EEG power in the theta band at frontal, central and parietal electrode regions. Crucially, these effects were specific for the theta band, with no effects on activity in the other frequency bands. Rs2180619 showed no significant associations with theta power after Bonferroni correction. Taken together, we provide novel evidence in humans showing that genetic variability in the cannabinoid receptor 1 is associated with resting state EEG power in the theta frequency band. This extends prior findings of exogenous cannabinoid effects on theta power to the endogenous cannabinoid system.

Multifractal analysis of information processing in hippocampal neural ensembles during working memory under Δ⁹-tetrahydrocannabinol administration

BACKGROUND

Multifractal analysis quantifies the time-scale-invariant properties in data by describing the structure of variability over time. By applying this analysis to hippocampal interspike interval sequences recorded during performance of a working memory task, a measure of long-range temporal correlations and multifractal dynamics can reveal single neuron correlates of information processing.

NEW METHOD

Wavelet leaders-based multifractal analysis (WLMA) was applied to hippocampal interspike intervals recorded during a working memory task. WLMA can be used to identify neurons likely to exhibit information processing relevant to operation of brain-computer interfaces and nonlinear neuronal models.

RESULTS

Neurons involved in memory processing ("Functional Cell Types" or FCTs) showed a greater degree of multifractal firing properties than neurons without task-relevant firing characteristics. In addition, previously unidentified FCTs were revealed because multifractal analysis suggested further functional classification. The cannabinoid type-1 receptor (CB1R) partial agonist, tetrahydrocannabinol (THC), selectively reduced multifractal dynamics in FCT neurons compared to non-FCT neurons.

COMPARISON WITH EXISTING METHODS

WLMA is an objective tool for quantifying the memory-correlated complexity represented by FCTs that reveals additional information compared to classification of FCTs using traditional z-scores to identify neuronal correlates of behavioral events.

CONCLUSION

z-Score-based FCT classification provides limited information about the dynamical range of neuronal activity characterized by WLMA. Increased complexity, as measured with multifractal analysis, may be a marker of functional involvement in memory processing. The level of multifractal attributes can be used to differentially emphasize neural signals to improve computational models and algorithms underlying brain-computer interfaces.

Role of the endocannabinoid system in brain functions relevant for schizophrenia: an overview of human challenge studies with cannabis or ∆9-tetrahydrocannabinol (THC)

Accumulating evidence suggests involvement of the endocannabinoid system in the pathophysiology of schizophrenia, which signifies a potential application for this system in the treatment of this disorder. However, before new research can focus on potential treatments that work by manipulating the endocannabinoid system, it needs to be elucidated how this system is involved in symptoms of schizophrenia. Here we review human studies that investigated acute effects of cannabis or ∆9-tetrahydrocannabinol (THC) on brain functions that are implicated in schizophrenia. Results suggest that the impact of THC administration depends on the difficulty of the task performed. Impaired performance of cognitive paradigms is reported on more challenging tasks, which is associated with both activity deficits in temporal and prefrontal areas and a failure to deactivate regions of the default mode network. Comparable reductions in prefrontal activity and impairments in deactivation of the default mode network are seen in patients during performance of cognitive paradigms. Normal performance levels after THC administration demonstrated for less demanding tasks are shown to be related to either increased neural effort in task-specific regions ('neurophysiological inefficiency'), or recruitment of alternative brain areas, which suggests a change in strategy to meet cognitive demands. Particularly a pattern of performance and brain activity corresponding with an inefficient working memory system is consistently demonstrated in patients. These similarities in brain function between intoxicated healthy volunteers and schizophrenia patients provide an argument for a role of the endocannabinoid system in symptoms of schizophrenia, and further emphasize this system as a potential novel target for treatment of these symptoms.

Impact of Cannabis Use on the Development of Psychotic Disorders

The link between cannabis use and psychosis comprises three distinct relationships: acute psychosis associated with cannabis intoxication, acute psychosis that lasts beyond the period of acute intoxication, and persistent psychosis not time-locked to exposure. Experimental studies reveal that cannabis, tetrahydrocannabinol (THC) and synthetic cannabinoids reliably produce transient positive, negative, and cognitive symptoms in healthy volunteers. Case-studies indicate that cannabinoids can induce acute psychosis which lasts beyond the period of acute intoxication but resolves within a month. Exposure to cannabis in adolescence is associated with a risk for later psychotic disorder in adulthood; this association is consistent, temporally related, shows a dose-response, and is biologically plausible. However, cannabis is neither necessary nor sufficient to cause a persistent psychotic disorder. More likely it is a component cause that interacts with other factors to result in psychosis. The link between cannabis and psychosis is moderated by age at onset of cannabis use, childhood abuse and genetic vulnerability. While more research is needed to better characterize the relationship between cannabinoid use and the onset and persistence of psychosis, clinicians should be mindful of the potential risk of psychosis especially in vulnerable populations, including adolescents and those with a psychosis diathesis.

Impact of dronabinol on quantitative electroencephalogram (qEEG) measures of sleep in obstructive sleep apnea syndrome

STUDY OBJECTIVES

To determine the effects of dronabinol on quantitative electroencephalogram (EEG) markers of the sleep process, including power distribution and ultradian cycling in 15 patients with obstructive sleep apnea (OSA).

METHODS

EEG (C4-A1) relative power (% total) in the delta, theta, alpha, and sigma bands was quantified by fast Fourier transformation (FFT) over 28-second intervals. An activation ratio (AR = [alpha + sigma] / [delta + theta]) also was computed for each interval. To assess ultradian rhythms, the best-fitting cosine wave was determined for AR and each frequency band in each polysomnogram (PSG).

RESULTS

Fifteen subjects were included in the analysis. Dronabinol was associated with significantly increased theta power (p = 0.002). During the first half of the night, dronabinol decreased sigma power (p = 0.03) and AR (p = 0.03), and increased theta power (p = 0.0006). At increasing dronabinol doses, ultradian rhythms accounted for a greater fraction of EEG power variance in the delta band (p = 0.04) and AR (p = 0.03). Females had higher amplitude ultradian rhythms than males (theta: p = 0.01; sigma: p = 0.01). Decreasing AHI was associated with increasing ultradian rhythm amplitudes (sigma: p < 0.001; AR: p = 0.02). At the end of treatment, lower relative power in the theta band (p = 0.02) and lower AHI (p = 0.05) correlated with a greater decrease in sleepiness from baseline.

CONCLUSIONS

This exploratory study demonstrates that in individuals with OSA, dronabinol treatment may yield a shift in EEG power toward delta and theta frequencies and a strengthening of ultradian rhythms in the sleep EEG.

Gone to Pot - A Review of the Association between Cannabis and Psychosis

Cannabis is the most commonly used illicit drug worldwide, with ~5 million daily users worldwide. Emerging evidence supports a number of associations between cannabis and psychosis/psychotic disorders, including schizophrenia. These associations-based on case-studies, surveys, epidemiological studies, and experimental studies indicate that cannabinoids can produce acute, transient effects; acute, persistent effects; and delayed, persistent effects that recapitulate the psychopathology and psychophysiology seen in schizophrenia. Acute exposure to both cannabis and synthetic cannabinoids (Spice/K2) can produce a full range of transient psychotomimetic symptoms, cognitive deficits, and psychophysiological abnormalities that bear a striking resemblance to symptoms of schizophrenia. In individuals with an established psychotic disorder, cannabinoids can exacerbate symptoms, trigger relapse, and have negative consequences on the course of the illness. Several factors appear to moderate these associations, including family history, genetic factors, history of childhood abuse, and the age at onset of cannabis use. Exposure to cannabinoids in adolescence confers a higher risk for psychosis outcomes in later life and the risk is dose-related. Individuals with polymorphisms of COMT and AKT1 genes may be at increased risk for psychotic disorders in association with cannabinoids, as are individuals with a family history of psychotic disorders or a history of childhood trauma. The relationship between cannabis and schizophrenia fulfills many but not all of the standard criteria for causality, including temporality, biological gradient, biological plausibility, experimental evidence, consistency, and coherence. At the present time, the evidence indicates that cannabis may be a component cause in the emergence of psychosis, and this warrants serious consideration from the point of view of public health policy.

Functional connectivity and cannabis use in high-risk adolescents

BACKGROUND

Adolescence is a unique neurodevelopmental period when regions of the brain most able to assess risk and reward are still in development. Cannabis use during adolescence has been associated with persistent negative outcomes. Although measures of resting brain activity are useful in assessing functional connectivity, such measures have not been broadly applied in adolescent cannabis-users.

OBJECTIVES

The goal of the present study was to analyze the associations between cannabis use and resting brain activity in a sample of high-risk adolescents.

METHODS

Eighty-two high-risk youth between 14-18 years old were recruited from a juvenile justice day program. Youth completed a brief neurocognitive battery including assessments of cannabis use and a 5-minute resting functional magnetic resonance imaging (fMRI) scan. Intrinsic connectivity networks were extracted using the GIFT toolbox. Brain activity in a fronto-temporal network was compared in youth with high cannabis use vs. low cannabis use using an independent-samples t-test with alcohol use entered as a covariate.

RESULTS

Analysis revealed two elements within the fronto-temporal network related to cannabis use: one in middle frontal gyrus related to high cannabis use, and one in middle temporal gyrus related to low cannabis use. Only the frontal source survived application of a cluster size threshold and was significant at p < 0.005.

CONCLUSIONS

These results are consistent with patterns of activity in adult cannabis-users. The observed effect may reflect either pre-existing risk factors or near-term consequences of cannabis use. Prevention and intervention strategies that address fronto-temporal functioning may be particularly helpful in this population.

The effect of cannabis use on memory function: an update

Investigating the effects of cannabis use on memory function appears challenging. While early observational investigations aimed to elucidate the longer-term effects of cannabis use on memory function in humans, findings remained equivocal and pointed to a pattern of interacting factors impacting on the relationship between cannabis use and memory function, rather than a simple direct effect of cannabis. Only recently, a clearer picture of the chronic and acute effects of cannabis use on memory function has emerged once studies have controlled for potential confounding factors and started to investigate the acute effects of delta-9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD), the main ingredients in the extract of the cannabis plant in pharmacological challenge experiments. Relatively consistent findings have been reported regarding the acute impairments induced by a single dose of Δ9-THC on verbal and working memory. It is unclear whether they may persist beyond the intoxication state. In the long-term, these impairments seem particularly likely to manifest and may also persist following abstinence if regular and heavy use of cannabis strains high in Δ9-THC is started at an early age. Although still at an early stage, studies that employed advanced neuroimaging techniques have started to model the neural underpinnings of the effects of cannabis use and implicate a network of functional and morphological alterations that may moderate the effects of cannabis on memory function. Future experimental and epidemiological studies that take into consideration individual differences, particularly previous cannabis history and demographic characteristics, but also the precise mixture of the ingredients of the consumed cannabis are necessary to clarify the magnitude and the mechanisms by which cannabis-induced memory impairments occur and to elucidate underlying neurobiological mechanisms.

Dose-related behavioral, subjective, endocrine, and psychophysiological effects of the κ opioid agonist Salvinorin A in humans

BACKGROUND

Salvia divinorum (Salvia) is an increasingly popular recreational drug amongst adolescents and young adults. Its primary active ingredient, Salvinorin A (SA)-a highly selective agonist at the κ opiate receptor-is believed to be one of the most potent naturally occurring hallucinogens. However, there is little experimental data on the effects of SA in humans.

METHODS

In a 3-day, double-blind, randomized, crossover, counterbalanced study, the behavioral, subjective, cognitive, psychophysiological, and endocrine effects of 0 mg, 8 mg, and 12 mg of inhaled SA were characterized in 10 healthy individuals who had previously used Salvia.

RESULTS

SA produced psychotomimetic effects and perceptual alterations, including dissociative and somaesthetic effects, increased plasma cortisol and prolactin, and reduced resting electroencephalogram spectral power. The SA administration was associated with a rapid increase of its levels in the blood. SA did not produce euphoria, cognitive deficits, or changes in vital signs. The effects were transient and not dose-related. SA administration was very well-tolerated without acute or delayed adverse effects.

CONCLUSIONS

SA produced a wide range of transient effects in healthy subjects. The perceptual altering effects and lack of euphoric effects would explain its intermittent use pattern. Such a profile would also suggest a low addictive potential similar to other hallucinogens and consistent with κ opiate receptor agonism. Further work is warranted to carefully characterize a full spectrum of its effects in humans, to elucidate the underlying mechanisms involved, and to explore the basis for individual variability in its effects.

The effect of chronic cannabinoids on broadband EEG neural oscillations in humans

Animal and cellular work has shown that central cannabinoid-1 receptors modulate neural oscillations in the gamma range (40 Hz), which may be important for normal perceptual and cognitive processes. In order to assess the effect of cannabinoids on broadband-frequency neural oscillations in humans, the current study examined the effect of chronic cannabis use on auditory steady-state responses (ASSRs) utilizing electroencephalography (EEG). Passive ASSRs were assessed using varying rates of binaural stimulation (auditory click-trains; 10-50 Hz in increments of 5 Hz; 80 dB SPL) in carefully screened cannabis users and controls. Chronic cannabis users (n=22; 12 h abstinence before study; positive 11-nor-9-carboxy-delta-9-tetrahydrocannabinol urine levels) and cannabis naïve controls (n=24) were evaluated. Time X frequency analyses on EEG data were performed using Fourier-based mean trial power (MTP) and phase-locking (inter-trial coherence; ITC). Transient ERPs to stimulus onset (auditory N100 components) were also evaluated. As predicted, a decrease in spectral power (MTP) at 40 Hz was observed in the cannabis group (p<0.018). No effects on phase-locking (ITC) or the N100 were observed. Further, within the cannabis group, lower 40 Hz power correlated with an earlier age of onset of cannabis use (p<0.04). These data suggest that chronic exposure to exogenous cannabinoids can alter the ability to generate neural oscillations, particularly in the gamma range. This is consistent with preclinical animal and cellular data, which may have implications for understanding the short- and long-term psychopharmacological effects of cannabis.

Manipulating brain connectivity with δ⁹-tetrahydrocannabinol: a pharmacological resting state FMRI study

Resting state-functional magnetic resonance imaging (RS-FMRI) is a neuroimaging technique that allows repeated assessments of functional connectivity in resting state. While task-related FMRI is limited to indirectly measured drug effects in areas affected by the task, resting state can show direct CNS effects across all brain networks. Hence, RS-FMRI could be an objective measure for compounds affecting the CNS. Several studies on the effects of cannabinoid receptor type 1 (CB(1))-receptor agonist δ(9)-tetrahydrocannabinol (THC) on task-dependent FMRI have been performed. However, no studies on the effects of cannabinoids on resting state networks using RS-FMRI have been published. Therefore, we investigated the effects of THC on functional brain connectivity using RS-FMRI. Twelve healthy volunteers (9 male, 3 female) inhaled 2, 6 and 6 mg THC or placebo with 90-minute intervals in a randomized, double blind, cross-over trial. Eight RS-FMRI scans of 8 min were obtained per occasion. Subjects rated subjective psychedelic effects on a visual analog scale after each scan, as pharmacodynamic effect measures. Drug-induced effects on functional connectivity were examined using dual regression with FSL software (FMRIB Analysis Group, Oxford). Eight maps of voxel-wise connectivity throughout the entire brain were provided per RS-FMRI series with eight predefined resting-state networks of interest. These maps were used in a mixed effects model group analysis to determine brain regions with a statistically significant drug-by-time interaction. Statistical images were cluster-corrected, and results were Bonferroni-corrected across multiple contrasts. THC administration increased functional connectivity in the sensorimotor network, and was associated with dissociable lateralized connectivity changes in the right and left dorsal visual stream networks. The brain regions showing connectivity changes included the cerebellum and dorsal frontal cortical regions. Clear increases were found for feeling high, external perception, heart rate and cortisol, whereas prolactin decreased. This study shows that THC induces both increases and (to a lesser extent) decreases in functional brain connectivity, mainly in brain regions with high densities of CB(1)-receptors. Some of the involved regions could be functionally related to robust THC-induced CNS-effects that have been found in previous studies (Zuurman et al., 2008), such as postural stability, feeling high and altered time perception.

Effects of δ9-tetrahydrocannabinol on human working memory function

BACKGROUND

Evidence indicates involvement of the endocannabinoid (eCB) system in both the pathophysiology of schizophrenia and working memory (WM) function. Additionally, schizophrenia patients exhibit relatively strong WM deficits. These findings suggest the possibility that the eCB system is also involved in WM deficits in schizophrenia. In the present study, we examined if perturbation of the eCB system can induce abnormal WM activity in healthy subjects.

METHODS

A pharmacological functional magnetic resonance imaging study was conducted with a placebo-controlled, cross-over design, investigating effects of the eCB agonist Δ9-tetrahydrocannabinol on WM function in 17 healthy volunteers, by means of a parametric Sternberg item-recognition paradigm with five difficulty levels.

RESULTS

Performance accuracy was significantly reduced after Δ9-tetrahydrocannabinol. In the placebo condition, brain activity increased linearly with rising WM load. Δ9-Tetrahydrocannabinol administration enhanced activity for low WM loads and reduced the linear relationship between WM load and activity in the WM system as a whole and in left dorsolateral prefrontal cortex, inferior temporal gyrus, inferior parietal gyrus, and cerebellum in particular.

CONCLUSIONS

Δ9-Tetrahydrocannabinol enhanced WM activity network-wide for low loads, while reducing the load-dependent response for increasing WM loads. These results indicate that a challenged eCB system can induce both abnormal WM activity and WM performance deficits and provide an argument for the possibility of eCB involvement in WM deficits in schizophrenia.

Disruption of frontal θ coherence by Δ9-tetrahydrocannabinol is associated with positive psychotic symptoms

The main ingredient in cannabis, Δ(9)-tetrahydrocannabinol (THC), can elicit acute psychotic reactions in healthy individuals and precipitate relapse in schizophrenic patients. However, the neural mechanism of this is unknown. We tested the hypothesis that THC psychopathology is related to changes in electroencephalography (EEG) power or inter-regional coherence. In a within-subjects design, participants (n=16) were given intravenous THC (1.25 mg) or placebo under double-blind conditions, during EEG recordings. Using fast-Fourier transform, EEG data were analyzed for power and coherence in the delta (1-3.5 Hz), theta (3.5-7 Hz), alpha (8-13 Hz), beta (14-25 Hz), low-gamma (30-40 Hz), and high-gamma (60-70 Hz) bands during engagement in the n-back test of working memory (WM). Compared with placebo, THC evoked positive and negative psychotic symptoms, as measured by the positive and negative syndrome scale (p<0.001) and slowed WM performance (p<0.05). Under THC, theta power was specifically reduced, (p<0.001) regardless of WM load; however, the reduction showed no relationship with psychotic symptoms or WM impairment. Coherence between bi-frontal electrodes in the theta band was also reduced by THC (p<0.05) and these reductions correlated with the change-in positive psychotic symptoms (rho=0.79, p<0.001). Bi-frontal specificity was suggested by the absence of a relationship between psychotic symptoms and fronto-parietal coherence. The results reveal that the pro-psychotic effects of THC might be related to impaired network dynamics with impaired communication between the right and left frontal lobes.

How human electrophysiology informs psychopharmacology: from bottom-up driven processing to top-down control

This review surveys human event-related brain potential (ERP) and event-related magnetic field (ERF) approaches to psychopharmacology and psychopathology, and the way in which they complement behavioral studies and other neuroimaging modalities. The major paradigms involving ERP/ERF are P50 suppression, loudness-dependent auditory evoked potential (LDAEP), mismatch negativity (MMN), P300, mental chronometry, inhibitory control, and conflict processing (eg, error-related negativity (ERN)). Together these paradigms cover a range of more bottom-up driven to more top-down controlled processes. A number of relationships between the major neurotransmitter systems and electrocortical mechanisms are highlighted. These include the role of dopamine in conflict processing, and perceptual processing vs motor preparation; the role of serotonin in P50 suppression, LDAEP, and MMN; glutamate/NMDA and MMN; and the role of acetylcholine in P300 generation and memory-related processes. A preliminary taxonomy for these relationships is provided, which should be helpful in attuning possible new treatments or new applications of existing treatments to various disorders.

Acute effects of MDMA (3,4-methylenedioxymethamphetamine) on EEG oscillations: alone and in combination with ethanol or THC (delta-9-tetrahydrocannabinol)

RATIONALE

Typical users of 3,4-methylenedioxymethamphetamine (MDMA or "ecstasy") are polydrug users, combining MDMA with alcohol or cannabis [most active compound: delta-9-tetrahydrocannabinol (THC)].

OBJECTIVES

The aim of the present study was to investigate whether co-administration of alcohol or THC with MDMA differentially affects ongoing electroencephalogram (EEG) oscillations compared to the administration of each drug alone.

METHODS

In two separate experiments, 16 volunteers received four different drug conditions: (1) MDMA (100 mg); (2) alcohol clamp (blood alcohol concentration = 0.6‰) or THC (inhalation of 4, 6 and 6 mg, interval of 1.5 h); (3) MDMA in combination with alcohol or THC; and (4) placebo. Before and after drug administration, electroencephalography was recorded during an eyes closed resting state.

RESULTS

Theta and alpha power increased after alcohol intake compared to placebo and reduced after MDMA intake. No interaction between alcohol and MDMA was found. Significant MDMA x THC effects for theta and lower-1-alpha power indicated that the power attenuation after the combined intake of MDMA and THC was less than the sum of each drug alone. For the lower-2-alpha band, the intake of MDMA or THC alone did not significantly affect power, but the intake of combined MDMA and THC significantly decreased lower-2-alpha power.

CONCLUSIONS

The present findings indicate that the combined intake of MDMA and THC, but not of MDMA and alcohol, affects ongoing EEG oscillations differently than the sum of either one drug alone. Changes in ongoing EEG oscillations may be related to the impaired task performance that has often been reported after drug intake.

Identifying robust and sensitive frequency bands for interrogating neural oscillations

Recent years have seen an explosion of interest in using neural oscillations to characterize the mechanisms supporting cognition and emotion. Oftentimes, oscillatory activity is indexed by mean power density in predefined frequency bands. Some investigators use broad bands originally defined by prominent surface features of the spectrum. Others rely on narrower bands originally defined by spectral factor analysis (SFA). Presently, the robustness and sensitivity of these competing band definitions remains unclear. Here, a Monte Carlo-based SFA strategy was used to decompose the tonic ("resting" or "spontaneous") electroencephalogram (EEG) into five bands: delta (1-5Hz), alpha-low (6-9Hz), alpha-high (10-11Hz), beta (12-19Hz), and gamma (>21Hz). This pattern was consistent across SFA methods, artifact correction/rejection procedures, scalp regions, and samples. Subsequent analyses revealed that SFA failed to deliver enhanced sensitivity; narrow alpha sub-bands proved no more sensitive than the classical broadband to individual differences in temperament or mean differences in task-induced activation. Other analyses suggested that residual ocular and muscular artifact was the dominant source of activity during quiescence in the delta and gamma bands. This was observed following threshold-based artifact rejection or independent component analysis (ICA)-based artifact correction, indicating that such procedures do not necessarily confer adequate protection. Collectively, these findings highlight the limitations of several commonly used EEG procedures and underscore the necessity of routinely performing exploratory data analyses, particularly data visualization, prior to hypothesis testing. They also suggest the potential benefits of using techniques other than SFA for interrogating high-dimensional EEG datasets in the frequency or time-frequency (event-related spectral perturbation, event-related synchronization/desynchronization) domains.