A preliminary study of functional brain activation among marijuana users during performance of a virtual water maze task

Effects of Cannabis Use on Neurocognition: A Scoping Review of MRI Studies

Cannabis is one of the most commonly utilized recreational drugs. However, increasing evidence from the literature suggests harmful implications on cognition. Thus, the main aim of the current review is to summarize literature findings pertaining to the impact of cannabis on neurocognitive skills, focusing on the imaging biomarkers provided by MRI. Two reviewers navigated the literature independently using four main search engines including PubMed and Cochrane. Articles were first evaluated through their title and abstract, followed by full-text assessment. Study characteristics and findings were extracted, and the studies' quality was appraised. 47 articles were included. The majority of the studies were of a case-control design (66%), and the most studied neurocognitive skill was memory (40.4%). With task-based fMRI being the most commonly utilized MRI technique, findings have shown significantly varying decreased and increased neuronal activity within brain regions associated with the cognitive tasks performed. Results suggest that cannabis users are significantly suffering from cognitive deficits. The major significance of this review is attributed to highlighting the role of MRI. Future research needs to delve more into validating the negative effects of cannabis, to enable stakeholders to take action to limit cannabis usage, to foster public health and wellbeing.

CannaCount: an improved metric for quantifying estimates of maximum possible cannabinoid exposure

Increasing numbers of individuals have access to cannabinoid-based products containing various amounts of delta-9-tetrahydrocannabinol (THC), cannabidiol (CBD), and other cannabinoids. Exposure to specific cannabinoids likely influences outcomes; however, current methods for quantifying cannabis exposure do not account for the cannabinoid concentrations of the products used. We developed CannaCount, an examiner-driven metric that quantifies estimated maximum possible cannabinoid exposure by accounting for variables related to cannabinoid concentration, duration, frequency, and quantity of use. To demonstrate feasibility and applicability, CannaCount was used to quantify estimated maximum THC and CBD exposure in 60 medical cannabis patients enrolled in a two-year, longitudinal, observational study. Medical cannabis patients reported using a variety of product types and routes of administration. Calculating estimated exposure to THC and CBD was possible for the majority of study visits, and the ability to generate estimated cannabinoid exposure improved over time, likely a function of improved product labeling, laboratory testing, and more informed consumers. CannaCount is the first metric to provide estimated maximum possible exposure to individual cannabinoids based on actual cannabinoid concentrations. This metric will ultimately facilitate cross-study comparisons and can provide researchers and clinicians with detailed information regarding exposure to specific cannabinoids, which will likely have significant clinical impact.

The role of endocannabinoid pathway in the neuropathology of Alzheimer's disease: Can the inhibitors of MAGL and FAAH prove to be potential therapeutic targets against the cognitive impairment associated with Alzheimer's disease?

Alzheimer's disease is a neurodegenerative disease characterized by progressive decline of cognitive function in combination with neuronal death. Current approved treatment target single dysregulated pathway instead of multiple mechanism, resulting in lack of efficacy in slowing down disease progression. The proclivity of endocannabinoid system to exert neuroprotective action and mitigate symptoms of neurodegeneration condition has received substantial interest. Growing evidence suggest the endocannabinoids (eCB) system, viz. anadamide (AEA) and arachidonoyl glycerol (2-AG), as potential therapeutic targets with the ability to modify Alzheimer's pathology by targeting the inflammatory, neurodegenerative and cognitive aspects of the disease. In order to modulate endocannabinoid system, number of agents have been reported amongst which are inhibitors of the monoacylglycerol (MAGL) and fatty acid amide hydrolase (FAAH), the enzymes that hydrolyses 2-AG and AEA respectively. However, little is known regarding the exact mechanistic signalling and their effects on pathophysiology and cognitive decline associated with Alzheimer's disease. Both MAGL and FAAH inhibitors possess fascinating properties that may offer a multi-faceted approach for the treatment of Alzheimer's disease such as potential to protect neurons from deleterious effect of amyloid-β, reducing phosphorylation of tau, reducing amyloid-β induced oxidative stress, stimulating neurotrophin to support brain intrinsic repair mechanism etc. Based on empirical evidence, MAGL and FAAH inhibitors might have potential for therapeutic efficacy against cognitive impairment associated with Alzheimer's disease. The aim of this review is to summarize the experimental studies demonstrating the polyvalent properties of MAGL or FAAH inhibitor compounds for the treatment of Alzheimer's disease, and also effect of these on learning and types of memories, which together encourage to study these compounds over other therapeutics targets. Further research in this direction would enhance the molecular mechanisms and development of applicable interventions for the treatment of Alzheimer's disease, which nevertheless stay as the primary unmet need.

Disrupted parahippocampal and midbrain function underlie slower verbal learning in adolescent-onset regular cannabis use

RATIONALE

Prolonged use of cannabis, the most widely used illicit drug worldwide, has been consistently associated with impairment in memory and verbal learning. Although the neurophysiological underpinnings of these impairments have been investigated previously using functional magnetic resonance imaging (fMRI), while performing memory tasks, the results of these studies have been inconsistent and no clear picture has emerged yet. Furthermore, no previous studies have investigated trial-by-trial learning.

OBJECTIVES

We aimed to investigate the neural underpinnings of impaired verbal learning in cannabis users as estimated over repeated learning trials.

METHODS

We studied 21 adolescent-onset regular cannabis users and 21 non-users using fMRI performed at least 12 h after last cannabis use, while they performed a paired associate verbal learning task that allowed us to examine trial-by-trial learning. Brain activation during repeated verbal encoding and recall conditions of the task was indexed using the blood oxygen level-dependent haemodynamic response fMRI signal.

RESULTS

There was a significant improvement in recall score over repeated trials indicating learning occurring across the two groups of participants. However, learning was significantly slower in cannabis users compared to non-users (p = 0.032, partial eta-squared = 0.108). While learning verbal stimuli over repeated encoding blocks, non-users displayed progressive increase in recruitment of the midbrain, parahippocampal gyrus and thalamus (p = 0.00939, partial eta-squared = 0.180). In contrast, cannabis users displayed a greater but disrupted activation pattern in these regions, which showed a stronger correlation with new word-pairs learnt over the same blocks in cannabis users than in non-users.

CONCLUSIONS

These results suggest that disrupted medial temporal and midbrain function underlie slower learning in adolescent-onset cannabis users.

Brain Activation during Memory Retrieval is Associated with Depression Severity in Women

Major depressive disorder (MDD) is a debilitating disorder that interferes with daily functioning, and that occurs at higher rates in women than in men. Structural and functional alterations in hippocampus and frontal lobe have been reported in MDD, which likely contribute to the multifaceted nature of MDD. One area impacted by MDD is hippocampal-mediated memory, which can be probed using a spatial virtual Morris water task (MWT). Women (n=24) across a spectrum of depression severity underwent functional magnetic resonance imaging (fMRI) during MWT. Depression severity, assessed via Beck Depression Inventory (BDI), was examined relative to brain activation during task performance. Significant brain activation was evident in areas traditionally implicated in spatial memory processing, including right hippocampus and frontal lobe regions, for retrieval > motor contrast. When BDI was included as a regressor, significantly less functional activation was evident in left hippocampus, and other non-frontal, task relevant regions for retrieval > rest contrast. Consistent with previous studies, depression severity was associated with functional alterations observed during spatial memory performance. These findings may contribute to understanding neurobiological underpinnings of depression severity and associated memory impairments, which may have implications for treatment approaches aimed at alleviating effects of depression in women.

Investigating the Residual Effects of Chronic Cannabis Use and Abstinence on Verbal and Visuospatial Learning

Rationale: Regular cannabis users have been shown to differ from non-using controls in learning performance. It is unclear if these differences are specific to distinct domains of learning (verbal, visuospatial), exacerbate with extent of cannabis exposure and dissipate with sustained abstinence. Objective: This study examines different domains of learning (verbal, visuospatial) in current and abstaining cannabis users, and the role of chronicity of use. Methods: In a cross-sectional design, we examined 127 psychiatrically healthy participants (65 female) with mean aged of 34 years. Of these, 69 individuals were current regular cannabis users (mean 15 years use), 12 were former cannabis users abstinent for ~2.5 yrs (after a mean of 16 years use), and 46 were non-cannabis using controls. Groups were compared on verbal learning performance assessed via the California Verbal Learning Test (CVLT-II) and for visuospatial learning measured with the Brown Location Test (BLT). We explored the association between CVLT/BLT performance and cannabis use levels in current and former users. Results: Current cannabis use compared to non-use was associated with worse performance on select aspects of verbal learning (Long Delay Cued Recall) and of visuospatial learning (Retroactive Interference and LD Rotated Recall). Prolonged abstinence was associated with altered verbal learning but intact visuospatial learning. There were non-significant correlations between distinct cannabis use measures, age and learning in both current and former users. Conclusions: Our findings suggest cannabis use status (current use, former use) affects different domains of learning (verbal and visuospatial) in a distinct fashion. These findings might be accounted for in the design of cognitive interventions aimed to support abstinence in cannabis users.

A Systematic Review of Human Neuroimaging Evidence of Memory-Related Functional Alterations Associated with Cannabis Use Complemented with Preclinical and Human Evidence of Memory Performance Alterations

Cannabis has been associated with deficits in memory performance. However, the neural correlates that may underpin impairments remain unclear. We carried out a systematic review of functional magnetic resonance imaging (fMRI) studies investigating brain functional alterations in cannabis users (CU) compared to nonusing controls while performing memory tasks, complemented with focused narrative reviews of relevant preclinical and human studies. Twelve studies employing fMRI were identified finding functional brain activation during memory tasks altered in CU. Memory performance studies showed CU performed worse particularly during verbal memory tasks. Longitudinal studies suggest that cannabis use may have a causal role in memory deficits. Preclinical studies have not provided conclusive evidence of memory deficits following cannabinoid exposure, although they have shown evidence of cannabinoid-induced structural and histological alteration. Memory performance deficits may be related to cannabis use, with lower performance possibly underpinned by altered functional activation. Memory impairments may be associated with the level of cannabis exposure and use of cannabis during developmentally sensitive periods, with possible improvement following cessation of cannabis use.

Intrinsic Frontolimbic Connectivity and Mood Symptoms in Young Adult Cannabis Users

Objective: The endocannbinoid system and cannabis exposure has been implicated in emotional processing. The current study examined whether regular cannabis users demonstrated abnormal intrinsic (a.k.a. resting state) frontolimbic connectivity compared to non-users. A secondary aim examined the relationship between cannabis group connectivity differences and self-reported mood and affect symptoms.

Method: Participants included 79 cannabis-using and 80 non-using control emerging adults (ages of 18–30), balanced for gender, reading ability, and age. Standard multiple regressions were used to predict if cannabis group status was associated with frontolimbic connectivity after controlling for site, past month alcohol and nicotine use, and days of abstinence from cannabis.

Results: After controlling for research site, past month alcohol and nicotine use, and days of abstinence from cannabis, cannabis users demonstrated significantly greater connectivity between left rACC and the following: right rACC (p = 0.001; corrected p = 0.05; f² = 0.55), left amygdala (p = 0.03; corrected p = 0.47; f² = 0.17), and left insula (p = 0.03; corrected p = 0.47; f² = 0.16). Among cannabis users, greater bilateral rACC connectivity was significantly associated with greater subthreshold depressive symptoms (p = 0.02).

Conclusions: Cannabis using young adults demonstrated greater connectivity within frontolimbic regions compared to controls. In cannabis users, greater bilateral rACC intrinsic connectivity was associated with greater levels of subthreshold depression symptoms. Current findings suggest that regular cannabis use during adolescence is associated with abnormal frontolimbic connectivity, especially in cognitive control and emotion regulation regions.

Interactions between recreational cannabis use and cognitive function: lessons from functional magnetic resonance imaging

Cannabis use is becoming increasingly popular as a growing number of states pass legislation to legalize cannabis and cannabis-derived products for recreational and/or medical purposes. Given the widespread use of cannabis, it is critical to understand the neural consequences related to cannabis use. In this review, we focus on evidence from functional magnetic resonance imaging studies that document acute and residual alterations in brain function during tasks spanning a variety of cognitive domains: executive function, attention and working memory, memory, motor skills, error monitoring, and reward and affective processing. Although it is clear that cannabis affects brain function, the findings are somewhat inconsistent; variables that potentially affect study outcomes are outlined, including a discussion of the impact of chronological age and age of cannabis onset as well as length of abstinence at the time of assessment, which are important considerations when measuring cannabis use patterns. Inherent differences between recreational/adult cannabis use versus use for medical purposes are also discussed, given their importance to public policy decisions.

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.

Relationship between fMRI response during a nonverbal memory task and marijuana use in college students

Marijuana (MJ) is widely used among college students, with peak use between ages 18-22. Research suggests memory dysfunction in adolescent and young adult MJ users, but the neural correlates are unclear. We examined functional magnetic resonance imaging (fMRI) response during a memory task among college students with varying degrees of MJ involvement. Participants were 64 college students, ages 18-20, who performed a visual encoding and recognition task during fMRI. MJ use was ascertained for 3 months prior to scanning; 27 individuals reported past 3-month MJ use, and 33 individuals did not. fMRI response was modeled during encoding based on whether targets were subsequently recognized (correct encoding), and during recognition based on target identification (hits). fMRI response in left and right inferior frontal gyrus (IFG) and hippocampal regions of interest was examined between MJ users and controls. There were no group differences between MJ users and controls on fMRI response during encoding, although single sample t-tests revealed that MJ users failed to activate the hippocampus. During recognition, MJ users showed less fMRI response than controls in right hippocampus (Cohen's d = 0.55), left hippocampus (Cohen's d = 0.67) and left IFG (Cohen's d = 0.61). Heavier MJ involvement was associated with lower fMRI response in left hippocampus and left IFG. This study provides evidence of MJ-related prefrontal and hippocampal dysfunction during recognition memory in college students. These findings may contribute to our previously identified decrements in academic performance in college MJ users and could have substantial implications for academic and occupational functioning.

Adolescent Hippocampal and Prefrontal Brain Activation During Performance of the Virtual Morris Water Task

The frontal cortex undergoes substantial structural and functional changes during adolescence and significant developmental changes also occur in the hippocampus. Both of these regions are notably vulnerable to alcohol and other substance use, which is typically initiated during adolescence. Identifying measures of brain function during adolescence, particularly before initiation of drug or alcohol use, is critical to understanding how such behaviors may affect brain development, especially in these vulnerable brain regions. While there is a substantial developmental literature on adolescent working memory, less is known about spatial memory. Thus, a virtual Morris water task (vMWT) was applied to probe function of the adolescent hippocampus. Multiband blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) data were acquired at 3T during task performance. Participants included 32 healthy, alcohol- and drug-naïve adolescents, 13–14 years old, examined at baseline of a 3-year longitudinal MRI study. Significantly greater BOLD activation was observed in the hippocampus and surrounding areas, and in prefrontal regions involved in executive function, during retrieval relative to motor performance. In contrast, significantly greater BOLD activation was observed in components of the default mode network, including frontal medial cortex, during the motor condition (when task demands were minimal) relative to the retrieval condition. Worse performance (longer path length) during retrieval was associated with greater activation of angular gyrus/supramarginal gyrus, whereas worse performance (longer path length/latency) during motor control was associated with less activation of frontal pole. Furthermore, while latency (time to complete task) was greater in females than in males, there were no sex differences in path length (accuracy), suggesting that females required more time to navigate the virtual environment, but did so as effectively as males. These findings demonstrate that performance of the vMWT elicits hippocampal and prefrontal activation patterns in early adolescence, similar to activation observed during spatial memory retrieval in adults. Given that this task is sensitive to hippocampal function, and that the adolescent hippocampus is notably vulnerable to the effects of alcohol and other substances, data acquired using this task during healthy adolescent development may provide a framework for understanding neurobiological impact of later initiation of use.

Marijuana matters: reviewing the impact of marijuana on cognition, brain structure and function, & exploring policy implications and barriers to research

The neurobiologic effects of cannabis, commonly referred to as 'marijuana' (MJ), have been studied for decades. The impact of recreational MJ use on cognition and measures of brain function and structure is outlined, and variables influencing study results are discussed, including age of the consumer, patterns of MJ use, variations in MJ potency, and the presence of additional cannabinoids. Although evidence suggests that chronic, heavy recreational MJ use is related to cognitive decrements and neural changes, particularly when use begins in adolescence, findings from studies of recreational MJ users may not be applicable to medical marijuana (MMJ) patients given differences in demographic variables, product selection, and reasons for use. Although additional research is needed to fully understand the impact of MJ and individual cannabinoids on the brain, current findings are beginning to inform public policy, including considerations for age limits, potential limits for some cannabinoids, and guidelines for use. However, barriers continue to impede researchers' ability to conduct studies that will guide policy change and provide vital information to consumers and patients regarding best practices and safest methods for use. The need for information is critical, as legalization of MJ for medical and recreational use is increasingly widespread.

Neuroimaging meta-analysis of cannabis use studies reveals convergent functional alterations in brain regions supporting cognitive control and reward processing

Lagging behind rapid changes to state laws, societal views, and medical practice is the scientific investigation of cannabis's impact on the human brain. While several brain imaging studies have contributed important insight into neurobiological alterations linked with cannabis use, our understanding remains limited. Here, we sought to delineate those brain regions that consistently demonstrate functional alterations among cannabis users versus non-users across neuroimaging studies using the activation likelihood estimation meta-analysis framework. In ancillary analyses, we characterized task-related brain networks that co-activate with cannabis-affected regions using data archived in a large neuroimaging repository, and then determined which psychological processes may be disrupted via functional decoding techniques. When considering convergent alterations among users, decreased activation was observed in the anterior cingulate cortex, which co-activated with frontal, parietal, and limbic areas and was linked with cognitive control processes. Similarly, decreased activation was observed in the dorsolateral prefrontal cortex, which co-activated with frontal and occipital areas and linked with attention-related processes. Conversely, increased activation among users was observed in the striatum, which co-activated with frontal, parietal, and other limbic areas and linked with reward processing. These meta-analytic outcomes indicate that cannabis use is linked with differential, region-specific effects across the brain.

Virtual Morris task responses in individuals in an abstinence phase from alcohol

The present study was aimed at examining spatial learning and memory, in 33 men and 12 women with alcohol use disorder (AUD) undergoing ethanol detoxification, by using a virtual Morris task. As controls, we recruited 29 men and 10 women among episodic drinkers without a history of alcohol addiction or alcohol-related diseases. Elevated latency to the first movement in all trials was observed only in AUD persons; furthermore, control women had longer latencies compared with control men. Increased time spent to reach the hidden platform in the learning phase was found for women of both groups compared with men, in particular during trial 3. As predicted, AUD persons (more evident in men) spent less time in the target quadrant during the probe trial; however, AUD women had longer latencies to reach the platform in the visible condition during trials 6 and 7 that resulted in a greater distance moved. As for the probe trial, men of both groups showed increased virtual locomotion compared with the women of both groups. The present investigation confirms and extends previous studies showing (i) different gender responses in spatial learning tasks, (ii) some alterations due to alcohol addiction in virtual spatial learning, and (iii) differences between AUD men and AUD women in spatial-behaviour-related paradigms.

Marijuana on the Mind? The Impact of Marijuana on Cognition, Brain Structure, and Brain Function, and Related Public Policy Implications

Although marijuana (MJ) has been used for thousands of years, the public’s opinion of MJ has shifted drastically over the past century, leaving many wondering about its potential risks and benefits. This article summarizes research detailing the impact of recreational MJ and related variables (frequency, magnitude, potency, and mode of MJ use) on cognition, brain structure, and brain function. MJ use, particularly at young ages, has been reported to undermine cognition, as well as alter brain structure and function. Furthermore, we discuss how data from recreational MJ studies, as well as more recent medical marijuana (MMJ) research findings, relate to legalization efforts. Considerations for policymakers, such as age limits, guidelines for safe use, and the therapeutic potential of certain constituents of MJ (i.e., cannabidiol), are also outlined. In recent years, policy has outpaced science; important areas in need of further research are noted.

Comorbid Cannabis and Tobacco Use in Adolescents and Adults

The prevalence of comorbid cannabis and tobacco use has been increasing among adolescents and adults and has been shown to be associated with a range of changes or deficits in physical, psychological and behavioral outcomes. Moreover, comorbid use has been shown to have a differential effect on the structure and function of the brain, especially as it relates to the reward circuitry and learning and memory. This interaction might be mediated by the involvement of the endocannabinoid system and alterations in dopamine signaling in regions associated with reward and cognitive functioning. While current findings demonstrate a differential effect of comorbid use on neurobiological and behavioral correlates compared with single substance use, additional studies are needed controlling for potential psychiatric comorbidities, age of onset of use and use of other substances. Understanding the neurobiological mechanisms associated with comorbid cannabis and tobacco use will be important in developing successful treatment outcomes in the future.

Cortical thinness and volume differences associated with marijuana abuse in emerging adults

BACKGROUND

The prevalence of marijuana (MJ) use among youth and its legalization for medical or recreational use has intensified public health endeavors of understanding MJ effects on brain structure and function. Studies indicate that MJ use is related to impaired cognitive performance, and altered functional brain activation and chemistry in adolescents and adults, but MJ effects on brain morphology in emerging adults are less understood.

METHODS

Fifteen MJ users (age 21.8±3.6, 2 females) and 15 non-user (NU) participants (age 22.3±3.5, 2 females) were included, demographically matched on age, education and alcohol use. High-resolution structural MR images were acquired at 3Tesla. Cortical thickness (CT) and volumetric analyses were performed using Freesurfer. A priori regions of interest (ROI) included orbitofrontal and cingulate cortices, amygdala, hippocampus and thalamus.

RESULTS

Whole brain CT analysis did not result in significant group differences in a priori ROIs but revealed MJ users had significantly less CT (i.e., thinness) in right fusiform gyrus (rFG) compared to NU (p<0.05). Thalamic volume was significantly smaller in MJ users compared to NU (right, p=0.05; left, p=0.01) and associated with greater non-planning (p<0.01) and overall impulsivity (p=0.04). There were no other group differences.

CONCLUSIONS

RFG cortical thinness and smaller thalamic volume in emerging adults is associated with MJ abuse. Furthermore, smaller thalamic volume associated with greater impulsivity contributes to growing evidence that the thalamus is neurobiologically perturbed by MJ use. Collectively, altered thalamic and rFG structural integrity may interfere with their known roles in regulating visuoperceptual and object information processing.

Effects of marijuana use on prefrontal and parietal volumes and cognition in emerging adults

RATIONALE

Chronic marijuana (MJ) use among adolescents has been associated with structural and functional abnormalities, particularly in developing regions responsible for higher order cognition.

OBJECTIVES

This study investigated prefrontal (PFC) and parietal volumes and executive function in emerging adult MJ users and explored potential gender differences.

METHODS

Participants (ages 18-25) were 27 MJ users and 32 controls without neurologic or psychiatric disorders or heavy other drug use. A series of multiple regressions examined whether group status, past year MJ use, and their interactions with gender predicted ROI volumes. Post hoc analyses consisted of brain-behavior correlations between volumes and cognitive variables and Fisher's z tests to assess group differences.

RESULTS

MJ users demonstrated significantly smaller medial orbitofrontal (mOFC; p = 0.004, FDR p = 0.024) and inferior parietal volumes (p = 0.04, FDR p = 0.12); follow-up regressions found that increased past year MJ use did not significantly dose-dependently predict smaller mOFC volume in a sub-sample of individuals with at least one past year MJ use. There were no significant gender interactions. There was a significant brain-behavior difference by group, such that smaller mOFC volumes were associated with poorer complex attention for MJ users (p < 0.05).

CONCLUSIONS

Smaller mOFC volumes among MJ users suggest disruption of typical neurodevelopmental processes associated with regular MJ use for both genders. These results highlight the need for longitudinal, multi-modal imaging studies providing clearer information on timing of neurodevelopmental processes and neurocognitive impacts of youth MJ initiation.

Spatial learning in men undergoing alcohol detoxification

Alcohol dependence is a major public health problem worldwide. Brain and behavioral disruptions including changes in cognitive abilities are common features of alcohol addiction. Thus, the present study was aimed to investigate spatial learning and memory in 29 alcoholic men undergoing alcohol detoxification by using a virtual Morris maze task. As age-matched controls we recruited 29 men among occasional drinkers without history of alcohol dependence and/or alcohol related diseases and with a negative blood alcohol level at the time of testing. We found that the responses to the virtual Morris maze are impaired in men undergoing alcohol detoxification. Notably they showed increased latencies in the first movement during the trials, increased latencies in retrieving the hidden platform and increased latencies in reaching the visible platform. These findings were associated with reduced swimming time in the target quadrant of the pool where the platform had been during the 4 hidden platform trials of the learning phase compared to controls. Such increasing latency responses may suggest motor control, attentional and motivational deficits due to alcohol detoxification.

Task-specific enhancement of hippocampus-dependent learning in mice deficient in monoacylglycerol lipase, the major hydrolyzing enzyme of the endocannabinoid 2-arachidonoylglycerol

Growing evidence indicates that the endocannabinoid system is important for the acquisition and/or extinction of learning and memory. However, it is unclear which endocannabinoid(s) play(s) a crucial role in these cognitive functions, especially memory extinction. To elucidate the physiological role of 2-arachidonoylglycerol (2-AG), a major endocannabinoid, in behavioral and cognitive functions, we conducted a comprehensive behavioral test battery in knockout (KO) mice deficient in monoacylglycerol lipase (MGL), the major hydrolyzing enzyme of 2-AG. We found age-dependent increases in spontaneous physical activity (SPA) in MGL KO mice. Next, we tested the MGL KO mice using 5 hippocampus-dependent learning paradigms (i.e., Morris water maze (MWM), contextual fear conditioning, novel object recognition test, trace eyeblink conditioning, and water-finding test). In the MWM, MGL KO mice showed normal acquisition of reference memory, but exhibited significantly faster extinction of the learned behavior. Moreover, they showed faster memory acquisition on the reversal-learning task of the MWM. In contrast, in the contextual fear conditioning, MGL KO mice tended to show slower memory extinction. In the novel object recognition and water-finding tests, MGL KO mice exhibited enhanced memory acquisition. Trace eyeblink conditioning was not altered in MGL KO mice throughout the acquisition and extinction phases. These results indicate that 2-AG signaling is important for hippocampus-dependent learning and memory, but its contribution is highly task-dependent.

Hippocampal-dorsolateral prefrontal coupling as a species-conserved cognitive mechanism: a human translational imaging study

Hippocampal-prefrontal cortex (HC-PFC) interactions are implicated in working memory (WM) and altered in psychiatric conditions with cognitive impairment such as schizophrenia. While coupling between both structures is crucial for WM performance in rodents, evidence from human studies is conflicting and translation of findings is complicated by the use of differing paradigms across species. We therefore used functional magnetic resonance imaging together with a spatial WM paradigm adapted from rodent research to examine HC-PFC coupling in humans. A PFC-parietal network was functionally connected to hippocampus (HC) during task stages requiring high levels of executive control but not during a matched control condition. The magnitude of coupling in a network comprising HC, bilateral dorsolateral PFC (DLPFC), and right supramarginal gyrus explained one-fourth of the variability in an independent spatial WM task but was unrelated to visual WM performance. HC-DLPFC coupling may thus represent a systems-level mechanism specific to spatial WM that is conserved across species, suggesting its utility for modeling cognitive dysfunction in translational neuroscience.

Sex differences in spatial navigation and perception in human adolescents and emerging adults

Males typically outperform females on spatial tasks, beginning early in life and continuing into adulthood. This study aimed to characterize age and sex differences in human spatial ability using a virtual Water Maze Task (vWMT), which is based on the classic Morris water maze spatial navigation task used in rodents. Performance on the vWMT and on a task assessing visuospatial perception, Mental Rotations Test (MRT), was examined in 33 adolescents and 39 emerging adults. For the vWMT, significant effects of age and sex were observed for path length in the target region (narrower spatial sampling), and heading error, with emerging adults performing better than adolescents, and an overall male advantage. For the MRT, males scored higher than females, but only in emerging adulthood. Overall, sex differences in visuospatial perception (MRT) emerge differently from those observed on a classic navigation task, with age and sex-specific superior vWMT performance likely related to the use of more efficient strategies. Importantly, these results extend the developmental timeline of spatial ability characterization to include adolescent males and females performing a virtual version of the classic vWMT.

Long-term effects of marijuana use on the brain

Questions surrounding the effects of chronic marijuana use on brain structure continue to increase. To date, however, findings remain inconclusive. In this comprehensive study that aimed to characterize brain alterations associated with chronic marijuana use, we measured gray matter (GM) volume via structural MRI across the whole brain by using voxel-based morphology, synchrony among abnormal GM regions during resting state via functional connectivity MRI, and white matter integrity (i.e., structural connectivity) between the abnormal GM regions via diffusion tensor imaging in 48 marijuana users and 62 age- and sex-matched nonusing controls. The results showed that compared with controls, marijuana users had significantly less bilateral orbitofrontal gyri volume, higher functional connectivity in the orbitofrontal cortex (OFC) network, and higher structural connectivity in tracts that innervate the OFC (forceps minor) as measured by fractional anisotropy (FA). Increased OFC functional connectivity in marijuana users was associated with earlier age of onset. Lastly, a quadratic trend was observed suggesting that the FA of the forceps minor tract initially increased following regular marijuana use but decreased with protracted regular use. This pattern may indicate differential effects of initial and chronic marijuana use that may reflect complex neuroadaptive processes in response to marijuana use. Despite the observed age of onset effects, longitudinal studies are needed to determine causality of these effects.

Neurofunctional changes in adolescent cannabis users with and without bipolar disorder

AIMS

To compare regional brain activation among adolescents with bipolar disorder and co-occurring cannabis use disorder.

DESIGN

Cross-sectional study.

SETTING

Cincinnati, OH, USA.

PARTICIPANTS

Adolescents with bipolar disorder (BP, n = 14), adolescents with cannabis use disorder (MJ, n = 13), adolescents with co-occurring cannabis use and bipolar disorders (BPMJ, n = 25) and healthy adolescents (HC, n = 15).

MEASUREMENTS

Cannabis craving, substance use, Blood Oxygenation Level Dependent (BOLD) signal assessed by the Marijuana Craving Questionnaire (MCQ), Teen-Addiction Severity Index (T-ASI) and a cannabis cue-reactivity task during a functional magnetic resonance imaging (fMRI) session, respectively.

FINDINGS

The BP group exhibited significantly greater brain activation than the BPMJ group in the right amygdala (F = 4.14, P = 0.046), left nucleus accumbens (F = 3.8, P = 0.02), left thalamus (F = 3.8, P < 0.05) and the right thalamus (F = 6.2, P = 0.02). The BP group exhibited significantly greater activation than the HC group in the left nucleus accumbens (F = 11.5, P = 0.0001), right thalamus (F = 4.9, P = 0.03) and the left striatum (F = 3.6, P = 0.04). Left amygdala activation of the BPMJ group trended towards being significantly negatively correlated with the number of joints smoked (R = -0.4, P = 0.06).

CONCLUSIONS

Bipolar adolescents with comorbid cannabis use do not exhibit the same over-activation of the regions involved in emotional processing as seen in adolescents with bipolar disorder alone. The absence of these findings in patients with comorbid bipolar and cannabis use disorders suggests that these individuals may have a unique endophenotype of bipolar disorder or that cannabis use may alter brain activation uniquely in bipolar disorder patients who use cannabis.

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.

Differential effects of binge drinking on learning and memory in emerging adults

Alterations in memory function due to alcohol exposure have been observed in both animal models and human populations. The human literature on neurocognitive consequences of binge alcohol use in emerging adults has not systematically investigated its potential negative impacts on visuospatial memory. For instance, these impacts have not yet been assessed using a human analogue of the Morris Water Maze Task (WMT), a key memory measure in the animal literature. Accordingly, this study compared performance between emerging adult binge drinkers (BD, n=22) and age- and sex-matched light drinkers (LD, n=29) using the Morris WMT, as well as verbal memory using the California Verbal Learning Test (CVLT). Emerging adult BD demonstrated worse performance on verbal learning and memory relative to LD. However, no significant group differences were observed on spatial learning and memory. Furthermore, no sex differences or interactions with drinking status were observed on either memory domain. These data suggest that in emerging adults who are at a heightened risk for alcohol abuse disorders, but who do not yet meet diagnostic criteria, verbal learning is uniquely impacted by the neurotoxic effects of binge drinking, whereas spatial learning is relatively spared between bouts of intoxication.

A Review of Magnetic Resonance Spectroscopy Studies in Marijuana using Adolescents and Adults

Marijuana (MJ) remains the most widely used illicit drug of abuse, and accordingly, is associated with adverse effects on mental and physical health, and neurocognitive decline. Studies investigating the neurobiology of underlying MJ effects have demonstrated structural and functional alterations in brain areas that contain moderate to high concentrations of cannabinoid (CB1) receptors and that are implicated in MJ-related cognitive decrements. Proton magnetic resonance spectroscopy (1H MRS), a non-invasive imaging technique used to assess neurochemistry, has been widely applied to probe a variety of substance-abusing populations. To date, however, there is a relative paucity of MRS published studies characterizing changes in neurometabolite concentrations in MJ users. Thus, the current review provides a summary of data from the eight existing MRS studies of MJ use in adolescents and adults, as well as interpretations and implications of study findings. Future MRS studies that address additional factors such as sex differences, onset and duration of use, abstinence and age, are warranted, and would lead to a more thorough characterization of potential neurochemical correlates of chronic MJ use, which would fill critical gaps in the existing literature.