The impact of early-onset cannabis use on functional brain correlates of working memory

Abnormal developmental of hippocampal subfields and amygdalar subnuclei volumes in young adults with heavy cannabis use: A three-year longitudinal study

BACKGROUND

Differences in the volumes of the hippocampus and amygdala have consistently been observed between young adults with heavy cannabis use relative to their non-using counterparts. However, it remains unclear whether the subfields of these functionally and structurally heterogenous regions exhibit similar patterns of change in young adults with long-term heavy cannabis use disorder (CUD).

OBJECTIVES

This study aims to investigate the effects of long-term heavy cannabis use in young adults on the subregional structures of the hippocampus and amygdala, as well as their longitudinal alterations.

METHODS

The study sample comprised 20 young adults with heavy cannabis use and 22 matched non-cannabis using healthy volunteers. All participants completed the Cannabis Use Disorder Identification Test (CUDIT) and underwent two T1-structural magnetic resonance imaging (MRI) scans, one at baseline and another at follow-up 3 years later. The amygdala, hippocampus, and their subregions were segmented on T1-weighted anatomical MRI scans, using a previously validated procedure.

RESULTS

At baseline, young adults with heavy CUD exhibited significantly larger volumes in several hippocampal (bilateral presubiculum, subiculum, Cornu Ammonis (CA) regions CA1, CA2-CA3, and right CA4-Dentate Gyrus (DG)) and amygdala (bilateral paralaminar nuclei, right medial nucleus, and right lateral nucleus) subregions compared to healthy controls, but these differences were attenuated at follow-up. Longitudinal analysis revealed an accelerated volumetric decrease in these subregions in young adults with heavy CUD relative to controls. Particularly, compared to healthy controls, significant accelerated volume decreases were observed in the right hippocampal subfields of the parasubiculum, subiculum, and CA4-DG. In the amygdala, similar trends of accelerated volumetric decreases were observed in the left central nucleus, right paralaminar nucleus, right basal nucleus, and right accessory basal nucleus.

CONCLUSIONS

The current findings suggest that long-term heavy cannabis use impacts maturational process of the amygdala and hippocampus, especially in subregions with high concentrations of cannabinoid type 1 receptors (CB1Rs) and involvement in adult neurogenesis.

Year-Long Cannabis Use for Medical Symptoms and Brain Activation During Cognitive Processes

Importance

Cannabis is increasingly being used to treat medical symptoms, but the effects on brain function in those using cannabis for these symptoms are not known.

Objective

To test whether 1 year of cannabis use for medical symptoms after obtaining a medical cannabis card was associated with increased brain activation during working memory, reward, and inhibitory control tasks, areas of cognition affected by cannabis.

Design, Setting, and Participants

This cohort study was conducted from July 2017 to July 2020 among participants from the greater Boston area who were recruited as part of a clinical trial of individuals seeking medical cannabis cards for anxiety, depression, pain, or insomnia symptoms. Participants were aged between 18 and 65 years. Exclusion criteria were daily cannabis use and cannabis use disorder at baseline. Data analysis was conducted from August 2021 to April 2024.

Main Outcomes and Measures

Outcomes were whole brain functional activation during tasks involving working memory, reward, and inhibitory control at baseline and after 1 year of medical cannabis card ownership.

Results

Imaging was collected from participants before and 1 year after obtaining medical cannabis cards, with 57 participants at baseline (38 female [66.7%]; 6 [10.5%] Black and 45 [78.9%] White participants; 1 [1.8%] Hispanic participant; median [IQR] age, 34.0 [24.0-51.0] years) and 54 participants at 1 year (37 female [68.5%]; 4 [7.4%] Black and 48 [88.9%] White participants; 1 [1.9%] Hispanic participant, median [IQR] age, 36.5 [25.0-51.0] years). Imaging was also collected in 32 healthy control participants at baseline (22 female [68.8%]; 2 [6.2%] Black and 27 [84.4%] White participants; 3 [9.4%] Hispanic participants; median [IQR] age, 33.0 [24.8-38.2] years). In all groups and at both time points, functional imaging revealed canonical activations of the probed cognitive processes. No statistically significant difference in brain activation between the 2 time points (baseline and 1 year) in those with medical cannabis cards and no associations between changes in cannabis use frequency and brain activation after 1 year were found.

Conclusions and Relevance

In this cohort study of adults obtaining medical cannabis cards for medical symptoms, no significant association between brain activation in the areas of cognition of working memory, reward, and inhibitory control and 1 year of cannabis use was observed. The results warrant further studies that probe the association of cannabis at higher doses, with greater frequency, in younger age groups, and with larger, more diverse cohorts.

A brief real-time fNIRS-informed neurofeedback training of the prefrontal cortex changes brain activity and connectivity during subsequent working memory challenge

Working memory (WM) represents a building-block of higher cognitive functions and a wide range of mental disorders are associated with WM impairments. Initial studies have shown that several sessions of functional near-infrared spectroscopy (fNIRS) informed real-time neurofeedback (NF) allow healthy individuals to volitionally increase activity in the dorsolateral prefrontal cortex (DLPFC), a region critically involved in WM. For the translation to therapeutic or neuroenhancement applications, however, it is critical to assess whether fNIRS-NF success transfers into neural and behavioral WM enhancement in the absence of feedback. We therefore combined single-session fNIRS-NF of the left DLPFC with a randomized sham-controlled design (N = 62 participants) and a subsequent WM challenge with concomitant functional MRI. Over four runs of fNIRS-NF, the left DLPFC NF training group demonstrated enhanced neural activity in this region, reflecting successful acquisition of neural self-regulation. During the subsequent WM challenge, we observed no evidence for performance differences between the training and the sham group. Importantly, however, examination of the fMRI data revealed that - compared to the sham group - the training group exhibited significantly increased regional activity in the bilateral DLPFC and decreased left DLPFC - left anterior insula functional connectivity during the WM challenge. Exploratory analyses revealed a negative association between DLPFC activity and WM reaction times in the NF group. Together, these findings indicate that healthy individuals can learn to volitionally increase left DLPFC activity in a single training session and that the training success translates into WM-related neural activation and connectivity changes in the absence of feedback. This renders fNIRS-NF as a promising and scalable WM intervention approach that could be applied to various mental disorders.

Impact of year-long cannabis use for medical symptoms on brain activation during cognitive processes

Importance

Cannabis is increasingly being used to treat medical symptoms, but the effects of cannabis use on brain function in those using cannabis for these symptoms is not known.

Objective

To test whether brain activation during working memory, reward, and inhibitory control tasks, areas of cognition impacted by cannabis, showed increases following one year of cannabis use for medical symptoms.

Design

This observational cohort study took place from July 2017 to July 2020 and is reported on in 2024.

Setting

Participants were from the greater Boston area.

Participants

Participants were recruited as part of a clinical trial based on seeking medical cannabis cards for anxiety, depression, pain, or sleep disorders, and were between 18 and 65 years. Exclusion criteria were daily cannabis use and cannabis use disorder at baseline.

Main Outcomes and Measures

Outcomes were whole brain functional activation during tasks involving working memory, reward and inhibitory control at baseline and after one year of cannabis use.

Results

Imaging was collected in participants before and one year after obtaining medical cannabis cards; 57 at baseline (38 female [66.7%]; mean [SD] age, 38.0 [14.6] years) at baseline, and 54 at one-year (37 female [68.5%]; mean [SD] age, 38.7 [14.3] years). Imaging was also collected in 32 healthy control participants (22 female [68.8%]; mean [SD] age, 33.8 [11.8] years) at baseline. In all groups and at both time points, functional imaging revealed canonical activations of the probed cognitive processes. No statistically significant difference in brain activation between the two timepoints (baseline and one-year) in those with medical cannabis cards and no association of changes in cannabis use frequency with brain activation were found.

Conclusions and Relevance

Findings suggest that adults do not show significant neural effects in the areas of cognition of working memory, reward, and inhibitory control after one year of cannabis use for medical symptoms. The results warrant further studies that probe effects of cannabis at higher doses, with greater frequency, in younger age groups, and with larger, more diverse cohorts.

Trial Registration

NCT03224468, https://clinicaltrials.gov/.

Nabilone Impairs Spatial and Verbal Working Memory in Healthy Volunteers

Background: Memory impairments and psychosis-like experiences can be adverse effects of cannabis use. However, reports on the cognitive impact of cannabis use are not consistent. There are also limited studies on the psychotomimetic effects of cannabinoid compounds to reveal the association between cannabis and psychosis. Therefore, we investigated the effect of acute cannabinoid intoxication on verbal working memory (VWM) and spatial working memory (SWM) following oral doses of the synthetic cannabinoid agonist, nabilone (1-2 mg, oral). We further investigated the effect of nabilone on psychosis-like experiences (schizotypy scores) and associations of schizotypy with VWM and SWM. Methods: Healthy participants (n=28) completed spatial and digit span tasks across different delay conditions (0, 6, 12, and 18 sec) after receiving nabilone (1-2 mg, PO) or placebo in a randomized, double-blind, counterbalanced, crossover manner. A subset of participants completed a short battery of schizotypy measures (n=25). Results: Nabilone impaired VWM (p=0.03, weak effect size η2=0.02) and SWM (p=0.00016, η2=0.08). Nabilone did not significantly change overall schizotypy scores. Schizotypy scores were negatively correlated with working memory (WM) averaged across all delays and both modalities, under placebo (ρ=-0.41, p=0.04). In addition, there were significant negative correlations between occasions of cannabis use and overall WM averaged scores across drug treatments (ρ=-0.49, p=0.007) and under placebo (ρ=-0.45, p=0.004). The results showed that the drug effect in the less frequent cannabis users was more pronounced on the SWM (p<0.01) and VWM (p<0.01), whereas there appeared to be little drug effect in the frequent cannabis users. Conclusion: Low doses of synthetic cannabinoid impaired SWM and VWM, indicating that exogenous activation of the cannabinoid system influences cognitive performance. Further, the results replicated previous findings that schizotypy is correlated with deficits in WM. Clinical Trial Registry Name: Nabilone and caffeine effects on the perceptions of visually, auditory, tactile and multimodal illusions in healthy volunteers. Clinical Trial Registration Number: CT-2018-CTN-02561 (Therapeutic Goods Administration Clinical Trial Registry) and ACTRN12618001292268 (The Australian New Zealand Clinical Trials Registry).

The Therapeutic Potential and Molecular Mechanisms Underlying the Neuroprotective Effects of Sativex® - A Cannabis-derived Spray

Sativex is a cannabis-based medicine that comes in the form of an oromucosal spray. It contains equal amounts of Δ9-tetrahydrocannabinol and cannabidiol, two compounds derived from cannabis plants. Sativex has been shown to have positive effects on symptoms of amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS), and sleep disorders. It also has analgesic, antiinflammatory, antitumoral, and neuroprotective properties, which make it a potential treatment option for other neurological disorders. The article reviews the results of recent preclinical and clinical studies that support the therapeutic potential of Sativex and the molecular mechanisms behind its neuroprotective benefits in various neurological disorders. The article also discusses the possible advantages and disadvantages of using Sativex as a neurotherapeutic agent, such as its safety, efficacy, availability, and legal status.

Nondisordered Cannabis Use Among US Adolescents

Importance

Cannabis use is increasingly viewed by adolescents as not harmful. Youths with cannabis use disorder (CUD) are recognized by clinicians as being at risk for adverse outcomes, yet little is known about the associations between subclinical cannabis use (ie, nondisordered cannabis use [NDCU]) and adverse psychosocial events.

Objective

To describe the prevalence and demographics of NDCU and to compare associations of cannabis use with adverse psychosocial events among adolescents with no cannabis use, NDCU, and CUD.

Design, Setting, and Participants

This cross-sectional study used a nationally representative sample derived from the 2015 to 2019 National Survey on Drug Use and Health. Participants were adolescents aged 12 to 17 years, separated into 3 distinct groups: nonuse (no recent cannabis use), NDCU (recent cannabis use below diagnostic threshold), and CUD. Analysis was conducted from January to May 2022.

Exposures

CUD, NDCU, or cannabis nonuse. NDCU was defined as endorsing recent cannabis use but not meeting the Diagnostic and Statistical Manual of Mental Disorders (Fifth Edition) (DSM-5) CUD criteria. CUD was defined using DSM-5 criteria.

Main Outcomes and Measures

The main outcomes were prevalence of adolescents meeting criteria for NDCU and associations between adverse psychosocial events and NDCU, adjusted for sociodemographic characteristics.

Results

The 68 263 respondents (mean [SD] age, 14.5 [1.7] years; 34 773 [50.9%] males) included in the analysis represented an estimated yearly mean of 25 million US adolescents during 2015 to 2019. Among respondents, 1675 adolescents (2.5%) had CUD, 6971 adolescents (10.2%) had NDCU, and 59 617 adolescents (87.3%) reported nonuse. Compared with nonusers, individuals with NDCU had approximately 2 to 4 times greater odds of all adverse psychosocial events examined, including major depression (adjusted odds ratio [aOR], 1.86; 95% CI, 1.67-2.08), suicidal ideation (aOR, 2.08; 95% CI, 1.88-2.29), slower thoughts (aOR, 1.76; 95% CI, 1.58-1.96), difficulty concentrating (aOR, 1.81; 95% CI, 1.65-2.00), truancy (aOR, 1.90; 95% CI, 1.67-2.16), low grade point average (aOR, 1.80; 95% CI, 1.62-2.00), arrest (aOR, 4.15; 95% CI, 3.17-5.43), fighting (aOR, 2.04; 95% CI, 1.80-2.31), and aggression (aOR, 2.16; 95% CI, 1.79-2.62). Prevalence of adverse psychosocial events was greatest for adolescents with CUD (range, 12.6% to 41.9%), followed by NDCU (range, 5.2% to 30.4%), then nonuse (range, 0.8% to 17.3%).

Conclusions and Relevance

In this cross-sectional study of US adolescents, past-year NDCU was approximately 4 times as prevalent as past-year CUD. A stepwise gradient association was observed for odds of adverse psychosocial events between adolescent NDCU and CUD. In the context of US normalization of cannabis use, prospective research into NDCU is necessary.

How do cannabis users mentally travel in time? Evidence from an fMRI study of episodic future thinking

RATIONALE

Episodic future thinking (EFT) is a cognitive function that allows individuals to imagine novel experiences that may happen in the future. Prior studies show that EFT is impaired in different groups of substance users. However, there is no evidence regarding the neurobiological mechanisms of EFT in cannabis users.

OBJECTIVES

We aimed to compare brain activations of regular cannabis users and non-using controls during an EFT fMRI task. Exploratory analyses were also conducted to investigate the association between EFT and cannabis use variables (e.g., duration of use, age onset, frequency of use).

METHODS

Twenty current cannabis users and 22 drug-naïve controls underwent an fMRI scanning session while completing a task involving envisioning future-related events and retrieval of past memories as a control condition. The EFT fMRI task was adapted from the autobiographical interview and composed of 20 auditory cue sentences (10 cues for past and 10 cues for future events). Participants were asked to recall a past or generate a future event, in response to the cues, and then rate their vividness after each response.

RESULTS

We found that cannabis users compared to non-user controls had lower activation within the cerebellum, medial and superior temporal gyrus, lateral occipital cortex, and occipital fusiform gyrus while envisioning future events. Cannabis users rated the vividness of past events significantly lower than non-users (P < 0.005). There were marginal group differences for rating the vividness of future events (P = 0.052). Significant correlations were also found between the medial and superior temporal gyrus activities and behavioral measures of EFT and episodic memory.

CONCLUSIONS

Cannabis users, compared to drug-naïve controls, have lower brain activation in EFT relevant regions. Thus, any attempts to improve aberrant EFT performance in cannabis users may benefit from EFT training.

Systematic review of structural and functional neuroimaging studies of cannabis use in adolescence and emerging adulthood: evidence from 90 studies and 9441 participants

Cannabis use peaks in adolescence, and adolescents may be more vulnerable to the neural effects of cannabis and cannabis-related harms due to ongoing brain development during this period. In light of ongoing cannabis policy changes, increased availability, reduced perceptions of harm, heightened interest in medicinal applications of cannabis, and drastic increases in cannabis potency, it is essential to establish an understanding of cannabis effects on the developing adolescent brain. This systematic review aims to: (1) synthesize extant literature on functional and structural neural alterations associated with cannabis use during adolescence and emerging adulthood; (2) identify gaps in the literature that critically impede our ability to accurately assess the effect of cannabis on adolescent brain function and development; and (3) provide recommendations for future research to bridge these gaps and elucidate the mechanisms underlying cannabis-related harms in adolescence and emerging adulthood, with the long-term goal of facilitating the development of improved prevention, early intervention, and treatment approaches targeting adolescent cannabis users (CU). Based on a systematic search of Medline and PsycInfo and other non-systematic sources, we identified 90 studies including 9441 adolescents and emerging adults (n = 3924 CU, n = 5517 non-CU), which provide preliminary evidence for functional and structural alterations in frontoparietal, frontolimbic, frontostriatal, and cerebellar regions among adolescent cannabis users. Larger, more rigorous studies are essential to reconcile divergent results, assess potential moderators of cannabis effects on the developing brain, disentangle risk factors for use from consequences of exposure, and elucidate the extent to which cannabis effects are reversible with abstinence. Guidelines for conducting this work are provided.

Chronic tobacco smoking, impaired reward-based decision-making, and role of insular cortex: A comparison between early-onset smokers and late-onset smokers

INTRODUCTION

The literature suggests that tobacco smoking may have a neurotoxic effect on the developing adolescent brain. Particularly, it may impair the decision-making process of early-onset smokers (<16 years), by rendering them more prone to impulsive and risky choices toward rewards, and therefore more prone to smoking relapses, in comparison to late-onset smokers (≥16 years). However, no study has ever investigated reward-based decision-making and structural brain differences between early-onset smokers and late-onset smokers.

METHODS

Computerized measures of reward-based decision-making [Cambridge Gambling Task (CGT); 5-trials adjusting delay discounting task (ADT-5)] were administered to 11 early-onset smokers (mean age at regular smoking initiation = 13.2 years), 17 late-onset smokers (mean age at regular smoking initiation = 18.0 years), and 24 non-smoker controls. Voxel-based morphometry (VBM) was utilized to investigate the gray matter (GM) and white matter (WM) volume differences in fronto-cortical and striatal brain regions between early-onset smokers, late-onset smokers, and non-smokers.

RESULTS

Early-onset smokers displayed a riskier decision-making behavior in comparison to non-smokers as assessed by the CGT (p < 0.01, Cohen's f = 0.48). However, no significant differences (p > 0.05) in reward-based decision-making were detected between early-onset smokers and late-onset smokers. VBM results revealed early-onset smokers to present lower GM volume in the bilateral anterior insular cortex (AI) in comparison to late-onset smokers and lower WM volume in the right AI in comparison to late-onset smokers.

CONCLUSION

Impairments in reward-based decision-making may not be affected by tobacco smoking initiation during early adolescence. Instead, lower GM and WM volume in the AI of early-onset smokers may underline a vulnerability to develop compulsive tobacco seeking and smoking behavior during adulthood.

Cannabis Use and Neuroadaptation: A Call for Δ 9 -Tetrahydrocannabinol Challenge Studies

Currently, the assessment of the neurobehavioral consequences of repeated cannabis use is restricted to studies in which brain function of chronic cannabis users is compared to that of non-cannabis using controls. The assumption of such studies is that changes in brain function of chronic users are caused by repeated and prolonged exposure to acute cannabis intoxication. However, differences in brain function between chronic cannabis users and non-users might also arise from confounding factors such as polydrug use, alcohol use, withdrawal, economic status, or lifestyle conditions. We propose a methodology that highlights the relevance of acute Δ⁹-tetrahydrocannabinol (THC) dosing studies for a direct assessment of neuroadaptations in chronic cannabis users. The approach includes quantification of neurochemical, receptor, and functional brain network changes in response to an acute cannabis challenge, as well as stratification of cannabis using groups ranging from occasional to cannabis-dependent individuals. The methodology allows for an evaluation of THC induced neuroadaptive and neurocognitive changes across cannabis use history, that can inform neurobiological models on reward driven, compulsive cannabis use.

Context dependent differences in working memory related brain activity in heavy cannabis users

RATIONALE

Compromised cognitive control in cannabis use-tempting situations is thought to play a key role in the development of cannabis use disorders. However, little is known about how exposure to cannabis cues and contexts may influence cognitive control and the underlying neural mechanisms in cannabis users.

OBJECTIVES

Working memory (WM) is an attention reliant executive function central to cognitive control. In this study, we investigated how distracting cannabis words affected WM load-dependent performance and related brain activity in near-daily cannabis users (N = 36) relative to controls (N = 33).

METHODS

Brain activity was recorded during a novel N-back flanker WM task with neutral and cannabis flankers added as task-irrelevant distractors.

RESULTS

On a behavioural level, WM performance did not differ between groups, and the presence of cannabis flankers did not affect performance. However, in cannabis users compared to controls, the presence of cannabis flankers reduced WM load-related activity in multiple regions, including the insula, thalamus, superior parietal lobe and supramarginal gyrus.

CONCLUSIONS

The group specificity of these effects suggest that cannabis users might differ from controls in the way they process cannabis-related cues and that cannabis cue exposure could interfere with other cognitive processes under cognitively demanding circumstances. Future studies should focus on the role of context in cognitive control-related processes like WM and attention to further elucidate potential cognitive impairments in heavy cannabis users and how these relate to loss of control over drug seeking itself.

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.

Cannabis use-related working memory deficit mediated by lower left hippocampal volume

The association between cannabis exposure and working memory impairment and its neural substrates remain unclear. In this cross-sectional observational study, we investigated this by examining the relationship between frequency of exposure to cannabis, working memory performance and regional brain volumes and tested whether lower volumes of cortical and subcortical structures mediate the association between cannabis exposure and working memory deficit using the Human Connectome Project data from 234 individuals with self-reported cannabis exposure and 174 individuals unexposed to cannabis. We tested the relationship between self-reported frequency of cannabis exposure and list-sorting working memory task performance (total number of correct responses), between T1 weighted MRI-derived regional grey-matter volumes and working memory task performance as well as between frequency of cannabis exposure and brain volumes after controlling for potential confounders. Finally, mediation analysis was carried out to test whether deficit in working memory performance associated with cannabis use was mediated by its association with lower grey-matter volume. Participants who reported higher frequency of cannabis use tended to have lower number of correct responses in the list-sorting working memory task and lower bilateral hippocampal volumes. Association between severity of cannabis exposure as indexed by frequency of cannabis use and impairment in working memory was mediated by lower left hippocampal volume in cannabis users. We report evidence in support of the left hippocampus volume-mediated working memory impairment associated with recreational cannabis exposure. Future studies employing prospective longitudinal design are necessary to examine the cause-effect relationships of cannabis exposure on working memory and brain volumes.

Disentangling the lasting effects of adolescent cannabinoid exposure

Cannabis is the most widely used illicit substance among adolescents, and adolescent cannabis use is associated with various neurocognitive deficits that can extend into adulthood. A growing body of evidence supports the hypothesis that adolescence encompasses a vulnerable period of development where exposure to exogenous cannabinoids can alter the normative trajectory of brain maturation. In this review, we present an overview of studies of human and rodent models that examine lasting effects of adolescent exposure. We include evidence from meta-analyses, longitudinal, or cross-sectional studies in humans that consider age of onset as a factor that contributes to the behavioral dysregulation and altered structural or functional development in cannabis users. We also discuss evidence from preclinical rodent models utilizing well-characterized or innovative routes of exposure, investigating the effects of dose and timing to produce behavioral deficits or alterations on a neuronal and behavioral level. Multiple studies from both humans and animals provide contrasting results regarding the magnitude of residual effects. Combined evidence suggests that exposure to psychoactive cannabinoids during adolescence has the potential to produce subtle, but lasting, alterations in neurobiology and behavior.

The Behavioral Sequelae of Cannabis Use in Healthy People: A Systematic Review

Background: Cannabis is known to have a broad range of effects on behavior, including experiencing a "high" and tranquility/relaxation. However, there are several adverse behavioral sequalae that can arise from cannabis use, depending on frequency of use, potency (e.g., THC content), age of onset, and cumulative exposure. This systematic review examined evidence for cannabis-related adverse behavioral sequalae in otherwise healthy human subjects. Methods: Following PRISMA guidelines, we conducted a systematic review of cross-sectional and longitudinal studies from 1990 to 2020 that identified cannabis-related adverse behavioral outcomes in subjects without psychiatric and medical co-morbidities from PubMed and PsychInfo searches. Key search terms included "cannabis" OR "tetrahydrocannabinol" OR "cannabidiol" OR "marijuana" AND "anxiety" OR "depression" OR "psychosis" OR "schizophrenia" "OR "IQ" OR "memory" OR "attention" OR "impulsivity" OR "cognition" OR "education" OR "occupation". Results: Our search detected a total of 2,870 studies, from which we extracted 124 relevant studies from the literature on cannabis effects in the non-clinical population. Effects of cannabis on several behavioral sequelae including cognition, motivation, impulsivity, mood, anxiety, psychosis intelligence, and psychosocial functioning were identified. The preponderance of the evidence suggests that frequency of cannabis use, THC (but not CBD) content, age of onset, and cumulative cannabis exposure can all contribute to these adverse outcomes in individuals without a pre-existing medical condition or psychiatric disorder. The strongest evidence for the negative effects of cannabis are for psychosis and psychosocial functioning. Conclusions: Although more research is needed to determine risk factors for development of adverse behavioral sequelae of cannabis use, these findings underline the importance of understanding vulnerability to the adverse effects of cannabis, which has implications for prevention and treatment of problematic cannabis use.

A Critical Review of the Role of the Cannabinoid Compounds Δ9-Tetrahydrocannabinol (Δ9-THC) and Cannabidiol (CBD) and their Combination in Multiple Sclerosis Treatment

Many people with MS (pwMS) use unregulated cannabis or cannabis products to treat the symptoms associated with the disease. In line with this, Sativex, a synthetic combination of cannabidiol (CBD) and Δ⁹-tetrahydrocannabinol (Δ⁹-THC) has been approved to treat symptoms of spasticity. In animals, CBD is effective in reducing the amounts of T-cell infiltrates in the spinal cord, suggesting CBD has anti-inflammatory properties. By doing this, CBD has shown to delay symptom onset in animal models of multiple sclerosis and slow disease progression. Importantly, combinations of CBD and Δ⁹-THC appear more effective in treating animal models of multiple sclerosis. While CBD reduces the amounts of cell infiltrates in the spinal cord, Δ⁹-THC reduces scores of spasticity. In human studies, the results are less encouraging and conflict with the findings in animals. Drugs which deliver a combination of Δ⁹-THC and CBD in a 1:1 ratio appear to be only moderately effective in reducing spasticity scores, but appear to be almost as effective as current front-line treatments and cause less severe side effects than other treatments, such as baclofen (a GABA-B receptor agonist) and tizanidine (an α2 adrenergic receptor agonist). The findings of the studies reviewed suggest that cannabinoids may help treat neuropathic pain in pwMS as an add-on therapy to already established pain treatments. It is important to note that treatment with cannabinoid compounds may cause significant cognitive dysfunction. Long term double-blind placebo studies are greatly needed to further our understanding of the role of cannabinoids in multiple sclerosis treatment.

Effects of early ketamine exposure on cerebral gray matter volume and functional connectivity

Ketamine has been used for medical purposes, most typically as an anesthetic, and recent studies support its use in the treatment of depression. However, ketamine tends to be abused by adolescents and young adults. In the current study, we examined the effects of early ketamine exposure on brain structure and function. We employed MRI to assess the effects of ketamine abuse on cerebral gray matter volume (GMV) and functional connectivity (FC) in 34 users and 19 non-users, employing covariates. Ketamine users were categorized as adolescent-onset and adult-onset based on when they were first exposed to ketamine. Imaging data were processed by published routines in SPM and AFNI. The results revealed lower GMV in the left precuneus in ketamine users, with a larger decrease in the adolescent-onset group. The results from a seed-based correlation analysis show that both ketamine groups had higher functional connectivity between left precuneus (seed) and right precuneus than the control group. Compared to controls, ketamine users showed decreased GMV in the right insula, left inferior parietal lobule, left dorsolateral prefrontal cortex/superior frontal gyrus, and left medial orbitofrontal cortex. These preliminary results characterize the effects of ketamine misuse on brain structure and function and highlight the influence of earlier exposure to ketamine on the development of the brain. The precuneus, a structure of central importance to cerebral functional organization, may be particularly vulnerable to the influences of early ketamine exposure. How these structural and functional brain changes may relate to the cognitive and affective deficits remains to be determined with a large cohort of participants.

Cognitive Function Impairments Linked to Alcohol and Cannabis Use During Adolescence: A Study of Gender Differences

Major neurocognitive changes occur during adolescence, making this phase one of the most critical developmental periods of life. Furthermore, this phase in life is also the time in which youth substance use begins. Several studies have demonstrated the differential associations of alcohol and cannabis use concerning the neurocognitive functioning of both males and females. Past and contemporary literature on gender-specific effects in neuroscience of addiction is predominantly based on cross-sectional datasets and data that is limited in terms of measurement variability. Given the importance of gender-specific effects in addiction studies, and in order to address the two above-mentioned gaps in the literature, the present study aimed to compare neurocognitive functioning of male and female adolescents in the context of cannabis and alcohol use, while employing a longitudinal design with multiple repeated measurements. Participants were 3,826 high school students (47% female; mean age, 12.7), who were recruited from 31 high schools in the greater Montreal area. Participants were requested to complete annual surveys for five consecutive years, from 7th to 11th grade, assessing their alcohol/cannabis use and neurocognitive functioning (working memory, delayed recall memory, perceptual reasoning, and inhibition control). The analytical strategy focused on the longitudinal association between each predictor (female, male) and each of the outcomes (domains of neurocognitive functioning). Multilevel linear models assessed the association of alcohol and cannabis consumption and the four domains of neurocognitive functioning. Results revealed a gender by within-subject interaction, suggesting a weaker effect of yearly fluctuation of cannabis use on working memory among males compared to females. Our findings suggest a different pattern of neurocognitive impairment of female and male working memory after using cannabis over the course of adolescence. Early initiation of cannabis use potentially results in more spatial working memory deficits in female adolescents. This may negatively influence young females' capacity in academic settings and lead to significant impairment in adulthood, which critically decreases the individual's quality of life.

Meta-analysis and review of functional neuroimaging differences underlying adolescent vulnerability to substance use

Adolescence is increasingly viewed as a sensitive period in the development of substance use disorders (SUDs). Neurodevelopmental 'dual-risk' theories suggest adolescent vulnerability to problematic substance use is driven by an overactive reward drive mediated by the striatum, and poor cognitive control mediated by the prefrontal cortex. To this end, there has been a growing number of neuroimaging studies examining cognitive and affective neural systems during adolescence for markers of vulnerability to problematic substance use. Here, we perform a coordinate-based meta-analysis on this emerging literature. Twenty-two task-based voxelwise fMRI studies with activation differences associated with substance use vulnerability, representative of approximately 1092 subjects, were identified through a systematic literature search (PubMed, Scopus) and coordinates of activation differences (N ​= ​190) were extracted. Adolescents were defined as 'at-risk' for problematic substance use based on a family history of SUD or through prospective prediction of substance use initiation or escalation. Multilevel kernel density analysis was used to identify the most consistent brain regions associated with adolescent substance use vulnerability. Across the included studies, substance use vulnerability was most reliably associated with activation differences in the striatum, where at-risk adolescents had hyper-activation in the dorsal subdivision (putamen). Follow-up analyses suggested striatal differences were driven by tasks sharing a motivational and/or reward component (e.g., monetary incentive) and common across subgroups of substance use risk (family history and prospective prediction studies). Analyses examining the role of psychiatric comorbidity revealed striatal activation differences were significantly more common in samples whose definition of substance use risk included cooccurring externalizing psychopathology. Furthermore, substance use risk meta-analytic results were no longer significant when excluding these studies, although this may reflect limitations in statistical power. No significant activation differences were observed in prefrontal cortex in any analysis. These results suggest striatal dysfunction, rather than prefrontal, may be a more primary neural feature of adolescent vulnerability to problematic substance use, possibly through a dimension of individual variability shared with externalizing psychopathology. However, our systematic literature search confirms this is still an emerging field. More studies, increased data sharing, and further quantitative integration are necessary for a comprehensive understanding of the neuroimaging markers of adolescent substance use risk.

Impaired cognitive performance under psychosocial stress in cannabis-dependent men is associated with attenuated precuneus activity

BACKGROUND

Deficient regulation of stress plays an important role in the escalation of substance use, addiction and relapse. Accumulating evidence suggests dysregulations in cognitive and reward-related processes and the underlying neural circuitry in cannabis dependence. However, despite the important regulatory role of the endocannabinoid system in the stress response, associations between chronic cannabis use and altered stress processing at the neural level have not been systematically examined.

METHODS

Against this background, the present functional MRI study examined psychosocial stress processing in cannabis-dependent men (n = 28) and matched controls (n = 23) using an established stress-induction paradigm (Montreal Imaging Stress Task) that combines computerized (adaptive) mental arithmetic challenges with social evaluative threat.

RESULTS

During psychosocial stress exposure, but not the no-stress condition, cannabis users demonstrated impaired performance relative to controls. In contrast, levels of experienced stress and cardiovascular stress responsivity did not differ from controls. Functional MRI data revealed that stress-induced performance deteriorations in cannabis users was accompanied by decreased precuneus activity and increased connectivity of this region with the superior frontal gyrus.

LIMITATIONS

Only male cannabis-dependent users were examined; the generalizability in female users remains to be determined.

CONCLUSION

Together, the present findings provide first evidence for exaggerated stress-induced cognitive performance deteriorations in cannabis users. The neural data suggest that deficient stress-related recruitment of the precuneus may be associated with the deterioration of performance at the behavioural level.

Probability and correlates of transition from cannabis use to DSM-5 cannabis use disorder: Results from a large-scale nationally representative study

INTRODUCTION AND AIMS

It has been previously reported that more than 34% of individuals who use cannabis may qualify for a diagnosis of DSM-IV cannabis abuse or dependence throughout their lifetime. The introduction of the DSM-5 cannabis use disorder (CUD) diagnostic criteria reflects several intrinsic changes in the perception of substance use disorders. However, little is known about the probability of transition from cannabis use to CUD over time nor about the sociodemographic and clinical correlates associated with this transition.

DESIGN AND METHODS

Participants were individuals ≥18 years interviewed in the National Epidemiologic Survey on Alcohol and Related Conditions-III in 2012-2013. Measurements included univariable and multivariable discrete-time survival analyses performed to examine the association between previously reported cannabis dependence predictors and the hazards of transitioning from cannabis use to CUD. Survival plots assessed the probability of transition from cannabis use to CUD over time since age of first use and differences in probability between predictor levels.

RESULTS

Among lifetime cannabis users (N = 11 272), lifetime probability of transition to CUD was approximately 27%. A higher probability of transition from cannabis use to CUD was observed in the following: men, participants belonging to an ethnic minority group, early-onset cannabis users and individuals who reported experiencing three or more childhood adverse events.

DISCUSSION AND CONCLUSIONS

This is the first study to explore transition from cannabis use to the DSM-5 CUD diagnosis. The current study identified specific predictors of this transition, which may assist in targeting at-risk populations.

Cannabis Use in Adolescence: A Review of Neuroimaging Findings

Objective: Shifting policies and widespread acceptance of cannabis for medical and/or recreational purposes have fueled worries of increased cannabis initiation and use in adolescents. In particular, the adolescent period is thought to be associated with an increased susceptibility to the potential harms of repeated cannabis use, due to being a critical period for neuromaturational events in the brain. This review investigates the neuroimaging evidence of brain harms attributable to adolescent cannabis use. Methods: PubMed and Scopus searches were conducted for empirical articles that examined neuroimaging effects in both adolescent cannabis users and adult user studies that explored the effect of age at cannabis use onset on the brain. Results: We found 43 studies that examined brain effect (structural and functional magnetic resonance imaging) in adolescent cannabis users and 20 that examined the link between onset age of cannabis use and brain effects in adult users. Studies on adolescent cannabis users relative to nonusers mainly implicate frontal and parietal regions and associated brain activation in relation to inhibitory control, reward, and memory. However, studies in adults are more mixed, many of which did not observe an effect of onset age of cannabis use on brain imaging metrics. Conclusions: While there is some evidence of compromised frontoparietal structure and function in adolescent cannabis use, it remains unclear whether the observed effects are specifically attributable to adolescent onset of use or general cannabis use-related factors such as depressive symptoms. The relative contribution of adolescent onset of cannabis use and use chronicity will have to be more comprehensively examined in prospective, longitudinal studies with more rigorous measures of cannabis use (dosage, exposure, dependence, constituent compounds such as the relative cannabinoid levels).

Is the Adolescent Brain at Greater Vulnerability to the Effects of Cannabis? A Narrative Review of the Evidence

Cannabis use during the critical neurodevelopmental period of adolescence, may lead to brain structural, functional, and histological alterations that may underpin some of the longer-term behavioral and psychological harms associated with it. The endocannabinoid system performs a key regulatory and homeostatic role, that undergoes developmental changes during adolescence making it potentially more susceptible to the effects of exposure to cannabis during adolescence. Here, we synthesize evidence from human studies of adolescent cannabis users showing alterations in cognitive performance as well as in brain structure and function with relevant preclinical evidence to summarize the current state of knowledge. We also focus on the limited evidence that speaks to the hypothesis that cannabis use during adolescence, may pose a greater risk than use during adulthood, identify gaps in current evidence and suggest directions for new research. Existing literature is consistent with the association of cannabis use during adolescence and neurological changes. Adolescence cannabis users show altered functional connectivity within known functional circuits, that may underlie inefficient recruitment of brain regions, as largely increased functional activation has been observed compared to controls. This disruption in some cases may contribute to the development of adverse mental health conditions; increasing the chances or accelerating the onset, of their development. Preclinical evidence, further supports disruption from cannabis use being specific to the developmental period. Future studies are required to better investigate adolescent cannabis use with more accuracy using better defined groups or longitudinal studies and examine the permanency of these changes following caseation of use. Furthermore, research is required to identify heritable risk factors to cannabis use. There is a need for caution when considering the therapeutic potential of cannabis for adolescence and particularly in public discourse leading to potential trivialization of possible harm from cannabis use in adolescence. Current evidence indicates that adolescence is a sensitive period during which cannabis use may result in adverse neurocognitive effects that appear to show a level of permanency into adulthood.

Cannabis Use and Consequences

As an increasing number of states legalize cannabis use for recreational and/or medical purposes, it is increasingly important to understand the neural and cognitive consequences of recreational cannabis use in adolescent consumers. Adolescence is marked by ongoing neuromaturational processes, making this a particularly vulnerable period, particularly regarding exposure to drugs, including cannabis. This review highlights evidence from studies documenting the neural impact of cannabis use in adolescence and explores mediating factors related to cannabis use.

Identification of biomarkers for the detection of subtle brain injury after cannabis and/or tramadol administration

Background

There is a need to identify biomarkers which could indicate the occurrence of brain injury in drug abuse.

Objectives

We aimed to investigate ubiquitin-C-terminal hydrolase-1 (UCH-L1), a neuronal cell body injury marker, the glial protein S-100 beta (S100β), and the glial fibrillary acidic protein (GFAP) as putative markers for neuronal injury due to cannabis, tramadol, or their combined use.

Materials and methods

Rats were treated with cannabis and/or tramadol subcutaneously daily for 6 weeks and UCH-L1, S100β, and GFAP were immunoassayed in the brain and serum.

Results

The results are as follows: (i) either cannabis or tramadol increased UCH-L1 and GFAP in the brain, (ii) serum UCH-L1 and GFAP increased by the highest dose of cannabis or tramadol, (iii) there was no additive effect for cannabis and tramadol on UCH-L1 or GFAP level in the brain or serum, (iv) S100β decreased in the brain by 5–20 mg/kg of cannabis and in the serum following 20 mg/kg of cannabis, and (v) S100β levels increased in the brain after 20 mg/kg of tramadol but decreased the brain and serum after both cannabis and tramadol. Cytoplasmic vacuolations, apoptotic cells, and gliosis were observed in the brain tissue of cannabis and/or tramadol-treated rats.

Conclusions

These results suggest that changes in UCH-L1, GFAP, or S100β are likely to reflect neurotoxicity and serum levels could be used to detect neuronal damage in chronic users.

Cannabis effects on brain structure, function, and cognition: considerations for medical uses of cannabis and its derivatives

Background: Cannabis is the most widely used illicit substance worldwide, and legalization for recreational and medical purposes has substantially increased its availability and use in the United States.Objectives: Decades of research have suggested that recreational cannabis use confers risk for cognitive impairment across various domains, and structural and functional differences in the brain have been linked to early and heavy cannabis use.Methods: With substantial evidence for the role of the endocannabinoid system in neural development and understanding that brain development continues into early adulthood, the rising use of cannabis in adolescents and young adults raises major concerns. Yet some formulations of cannabinoid compounds are FDA-approved for medical uses, including applications in children.Results: Potential effects on the trajectory of brain morphology and cognition, therefore, should be considered. The goal of this review is to update and consolidate relevant findings in order to inform attitudes and public policy regarding the recreational and medical use of cannabis and cannabinoid compounds.Conclusions: The findings point to considerations for age limits and guidelines for use.

Cannabis-associated impairments in the fading affect bias and autobiographical memory specificity

We investigated potential relationships between cannabis use and 2 phenomena associated with autobiographical remembering: the fading affect bias (FAB) and memory specificity. The FAB is an emotional affect regulation mechanism that is observed when the intensity of affect associated with experiencing negative memories fades faster than the intensity of affect associated with experiencing positive memories. Memory specificity refers to the level of detail with which events are recalled. No studies have examined the relationships between cannabis use, the FAB, and memory specificity simultaneously. Chronic cannabis users (N = 47) and non-users (N = 52) recalled and described positive and negative autobiographical events and rated the affective intensity for the events at the time of occurrence and at time of test. Participants retrieved additional memories using a sentence-completion recall task, which were coded for specificity. Cannabis users showed reduced fading affect for unpleasant events and reduced memory specificity compared to non-users.

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.

Shifted balance of dorsal versus ventral striatal communication with frontal reward and regulatory regions in cannabis-dependent males

The transition from voluntary to addictive behavior is characterized by a loss of regulatory control in favor of reward driven behavior. Animal models indicate that this process is neurally underpinned by a shift in ventral-dorsal striatal control of behavior; however, this shift has not been directly examined in humans. The present resting state functional magnetic resonance imaging (fMRI) study employed a two-step approach to: (a) precisely map striatal alterations using a novel, data-driven network classification strategy combining intrinsic connectivity contrast with multivoxel pattern analysis and, (b) to determine whether a ventral to dorsal striatal shift in connectivity with reward and regulatory control regions can be observed in abstinent (28 days) male cannabis-dependent individuals (n = 24) relative to matched controls (n = 28). Network classification revealed that the groups can be reliably discriminated by global connectivity profiles of two striatal regions that mapped onto the ventral (nucleus accumbens) and dorsal striatum (caudate). Subsequent functional connectivity analysis demonstrated a relative shift between ventral and dorsal striatal communication with fronto-limbic regions that have been consistently involved in reward processing (rostral anterior cingulate cortex [ACC]) and executive/regulatory functions (dorsomedial prefrontal cortex [PFC]). Specifically, in the cannabis-dependent subjects, connectivity between the ventral striatum with the rostral ACC increased, whereas both striatal regions were uncoupled from the regulatory dorsomedial PFC. Together, these findings suggest a shift in the balance between dorsal and ventral striatal control in cannabis dependence. Similar changes have been observed in animal models and may promote the loss of control central to addictive behavior.

Fronto-striatal effective connectivity of working memory in adults with cannabis use disorder

Previous working memory (WM) studies found that relative to controls, subjects with cannabis use disorder (CUD) showed greater brain activation in some regions (e.g., left [L] and right [R] ventrolateral prefrontal cortex [VLPFC], and L dorsolateral prefrontal cortex [L-DLPFC]), and lower activation in other regions (e.g., R-DLPFC). In this study, effective connectivity (EC) analysis was applied to functional magnetic resonance imaging data acquired from 23 CUD subjects and 23 controls (two groups matched for sociodemographic factors and substance use history) while performing an n-back WM task with interleaved 2-back and 0-back periods. A 2-back minus 0-back modulator was defined to measure the modulatory changes of EC corresponding to the 2-back relative to 0-back conditions. Compared to the controls, the CUD group showed smaller modulatory change in the R-DLPFC to L-caudate pathway, and greater modulatory changes in L-DLPFC to L-caudate, R-DLPFC to R-caudate, and R-VLPFC to L-caudate pathways. Based on previous fMRI studies consistently suggesting that greater brain activations are related to a compensatory mechanism for cannabis neural effects (less regional brain activations), the smaller modulatory change in the R-DLPFC to L-caudate EC may be compensated by the larger modulatory changes in the other prefrontal-striatal ECs in the CUD individuals.

Early Cannabis Use and Neurocognitive Risk: A Prospective Functional Neuroimaging Study

BACKGROUND

Retrospective neuroimaging studies have suggested an association between early cannabis onset and later neurocognitive impairment. However, these studies have been limited in their ability to distinguish substance use risk factors from cannabis-induced effects on neurocognition. We used a prospective cohort design to test whether neurocognitive differences preceded cannabis onset (substance use risk model) and if early cannabis use was associated with poorer neurocognitive development (cannabis exposure model).

METHODS

Participants (N = 85) completed a visuospatial working memory task during functional magnetic resonance imaging and multiple cognitive assessments (Wechsler Intelligence Scale for Children-IV, Cambridge Neuropsychological Test Automated Battery) at 12 years of age, before any reported cannabis use (baseline), and at 15 years of age (follow-up: N = 85 cognitive assessments, n = 67 neuroimaging). By follow-up, 22 participants reported using cannabis and/or failed a Δ⁹-tetrahydrocannabinol urine screen (users).

RESULTS

At baseline, group differences supported a risk model. Those who would initiate cannabis use by 15 years of age had activation differences in frontoparietal (increased) and visual association (decreased) regions and poorer executive planning scores (Stockings of Cambridge) compared with noninitiators. Limited support was found for a cannabis exposure model. At follow-up, activation in the cuneus displayed a significant cannabis dose-response relationship, although neither cannabis dose nor cuneus activation was associated with cognitive performance.

CONCLUSIONS

The purported neurocognitive effects of early cannabis onset may not be due to cannabis initiation alone but also driven by limitations or late development of neurocognitive systems predictive of substance use. In addition, more prolonged cannabis exposure may be required to observe the cognitive effects of early cannabis onset.

Early onset cigarette smokers exhibit greater P300 reactivity to smoking-related stimuli and report greater craving

Adolescence is a period during which a number of critical neuromaturation processes occur and the vulnerability for developing nicotine dependence is extremely high. Thus, early-onset (EO; age < 16 years old), relative to late-onset (LO; age ≥ 16 years old), tobacco smoking may be uniquely deleterious for developmentally immature systems that regulate neural signaling reactivity. This study investigated how age of tobacco smoking onset affects neurophysiological measures of smoking cue reactivity and reported craving in adult smokers. EO smokers (EOS; n = 8; 4 females), LO smokers (LOS; n = 10; 5 females), and healthy non-smokers (HNS; n = 10; 5 females) participated in an event-related potential (ERP) cue reactivity study with tactile and image stimuli. Participants handled neutral objects during one interval and smoking-related objects during a second interval. After each interval, they viewed smoking-related, neutral, or arousing images using an oddball paradigm. P300 ERPs and craving for tobacco were recorded during each session. P300 amplitudes were significantly higher in central midline (Cz) channel to smoking, but not neutral or arousing, images after handling smoking objects. Specifically, Cz P300 smoking amplitudes were significantly greater in EOS, relative to LOS and HNS, and associated with greater craving at baseline. There were no other group differences in mood or craving. EOS exhibited greater P300 reactivity to smoking-related stimuli, relative to LOS, suggesting a more sensitized neural response. EO smoking during early neuromaturation may alter neurophysiological signaling involved in responding to smoking-related stimuli, which could impact the outcome of smoking cessation interventions.

Working Memory Training for Adolescents With Cannabis Use Disorders: A Randomized Controlled Trial

Adolescent cannabis use is associated with working memory impairment. The present randomized controlled trial assigned adolescents ages 14 to 21 enrolled in cannabis use treatment to receive either working memory training (experimental group) or a control training (control group) as an adjunctive treatment. Cognitive function, drug use, and other outcomes were assessed before and after training. We observed few differences in cognitive, functional, or self-reported drug use outcomes as a function of training group, although tetrahydrocannabinol (THC) urinalysis results favored the experimental group. These findings are similar to previous studies in substance users, which have shown limited transfer effects for working memory training.

Adolescent cannabis use and brain systems supporting adult working memory encoding, maintenance, and retrieval

Given prior reports of adverse effects of cannabis use on working memory, an executive function with a protracted developmental course during adolescence, we examined associations between developmental patterns of cannabis use and adult working memory (WM) processes. Seventy-five adults with longitudinal assessments of cannabis use (60 with reported use, 15 with no reported use) and prenatal drug exposure assessment completed a spatial WM task during fMRI at age 28. All subjects passed a multi-drug urine screen on the day of testing and denied recreational drug use in the past week. A fast event-related design with partial trials was used to separate the BOLD response associated with encoding, maintenance, and retrieval periods of the WM task. Behavioral results showed that subjects who began using cannabis earlier in adolescence had longer reaction times (RT) than those with later initiation. Cannabis age of onset was further associated with reduced posterior parietal cortex (PPC) encoding BOLD activation, which significantly mediated age of onset WM RT associations. However, cannabis age of onset brain-behavior associations did not differ between groups with a single reported use and those with repeated use, suggesting age of onset effects may reflect substance use risk characteristics rather than a developmentally-timed cannabis exposure effect. Within repeated cannabis users, greater levels of total cannabis use were associated with performance-related increases in dorsolateral prefrontal cortex (DLPFC) activation during maintenance. This pattern of significant results remained unchanged with inclusion of demographic and prenatal measures as covariates. Surprisingly, however, at the group level, cannabis users generally performed better than participants who reported never using cannabis (faster RT, higher accuracy). We extend previous investigations by identifying that WM associations with cannabis age of onset may be primary to PPC stimulus encoding activity, while the amount of cannabis use is associated with DLPFC maintenance processes. Poorer performance of participants who reported never using cannabis and the consistency of cannabis age of onset associations across single and repeated users limit interpretation of direct developmental effects of cannabis on WM in adulthood.

Early onset tobacco cigarette smokers exhibit deficits in response inhibition and sustained attention

BACKGROUND

Initiation of cigarette smoking during adolescence coincides with structural and cognitive neuromaturation. Thus, early onset smokers (EOS; initiated <16 years old) may be at unique risk of altered development of executive function relative to late onset smokers (LOS; initiated >16 years old). This study quantified the effects of age of smoking onset on response impulsivity and inhibitory control using a novel smoking Go/NoGo task (Luijten et al., 2011).

METHODS

Nicotine deprived adult EOS (n = 10) and LOS (n = 10) and adult healthy non-smokers (HNS; n = 10) were shown smoking-related and neutral images with either a blue (Go) or yellow (NoGo) frame. Participants were instructed to respond to blue-framed Go trials quickly and accurately, and withhold responding for yellow-framed NoGo trials.

RESULTS

EOS made more Go response accuracy errors (p ≤ 0.02) and failed more frequently to inhibit responses to NoGo trials (p < 0.02) than LOS and HNS. EOS also made more errors in inhibiting responses to smoking-related (p ≤ 0.02) and neutral (p ≤ 0.02) NoGo trials. EOS reported greater baseline craving for cigarette smoking than LOS (p < 0.04), and craving was significantly associated with greater omission errors (p ≤ 0.04).

CONCLUSIONS

EOS exhibited greater difficulty than LOS in responding accurately to Go stimuli and withholding responses to both smoking and neutral NoGo stimuli, indicating greater response impulsivity, poor attention, and deficits in response inhibition. These findings suggest that EO smoking, in particular, contributes to diminished task-related attention and inhibitory control behaviors in adulthood and provide support for the tobacco-induced neurotoxicity of adolescent cognitive development (TINACD) theory (DeBry and Tiffany, 2008).

Altered orbitofrontal activity and dorsal striatal connectivity during emotion processing in dependent marijuana users after 28 days of abstinence

RATIONALE

Intact cognitive and emotional functioning is vital for the long-term success of addiction treatment strategies. Accumulating evidence suggests an association between chronic marijuana use and lasting alterations in cognitive brain function. Despite initial evidence for altered emotion processing in dependent marijuana users after short abstinence periods, adaptations in the domain of emotion processing after longer abstinence remain to be determined.

OBJECTIVE AND METHODS

Using task-based and resting state fMRI, the present study investigated emotion processing in 19 dependent marijuana users and 18 matched non-using controls after an abstinence period of > 28 days.

RESULTS

Relative to the control subjects, negative emotional stimuli elicited increased medial orbitofrontal cortex (mOFC) activity and stronger mOFC-dorsal striatal and mOFC-amygdala functional coupling in dependent marijuana users (p < 0.022, FWE-corrected). Furthermore, mOFC-dorsal striatal functional connectivity was increased at rest in marijuana users (p < 0.03, FWE-corrected). Yet, processing of positive stimuli and subjective ratings of valence and arousal were comparable in both groups.

CONCLUSIONS

Together, the present findings provide the first evidence for persisting emotion processing alterations in dependent marijuana users. Alterations might reflect long-term neural adaptations as a consequence of chronic marijuana use or predisposing risk factors for the development of marijuana dependence.

Impaired contrast sensitivity at low spatial frequency in cannabis users with early onset

The regular use of cannabis generates pronounced cognitive disorders, especially in users who begin before the age of 15-16. However, less is known about the impact of regular cannabis on visual function, especially in the case of early onset. Cannabinoid receptors (CB1) are expressed in areas of the visual system, like the thalamus and primary cortex, which might originate sensory disorders. Hence, we measured contrast sensitivity (CS) in three groups, i.e. cannabis users with late onset of cannabis use (after 16 years old), cannabis users with early onset". We used a constant method which allowed us to control for biased responses. Stimuli were presented at high and low spatial frequencies and in both static and dynamic conditions (8Hz). As contrast sensitivity is measured behaviorally based on an explicit response and could thus be impacted by attentional or vigilance disorders, participants' attention and vigilance were carefully monitored by means of the D2 test, CPT-AX for attention and pupillography for vigilance. Cannabis users with early onset were significantly impaired only at low spatial frequency. This effect was independent of response bias, vigilance and attention. These results show for the first time that early cannabis use impacts contrast sensitivity at low spatial frequency.

Adolescent cannabis use, change in neurocognitive function, and high-school graduation: A longitudinal study from early adolescence to young adulthood

The main objective of this prospective longitudinal study was to investigate bidirectional associations between adolescent cannabis use (CU) and neurocognitive performance in a community sample of 294 young men from ages 13 to 20 years. The results showed that in early adolescence, and prior to initiation to CU, poor short-term and working memory, but high verbal IQ, were associated with earlier age of onset of CU. In turn, age of CU onset and CU frequency across adolescence were associated with (a) specific neurocognitive decline in verbal IQ and executive function tasks tapping trial and error learning and reward processing by early adulthood and (b) lower rates of high-school graduation. The association between CU onset and change in neurocognitive function, however, was found to be accounted for by CU frequency. Whereas the link between CU frequency across adolescence and change in verbal IQ was explained (mediated) by high school graduation, the link between CU frequency and tasks tapping trial and error learning were independent from high school graduation, concurrent cannabis and other substance use, adolescent alcohol use, and externalizing behaviors. Findings support prevention efforts aimed at delaying onset and reducing frequency of CU.

Cognitive functioning of adolescent and young adult cannabis users in the Philadelphia Neurodevelopmental Cohort

Cannabis use in youth is rising and has been linked to deficits in cognitive functioning. However, cognitive findings have primarily been based on small samples of users seeking treatment, and few studies have evaluated cognition in occasional cannabis users. Here, we examined 4,568 adolescents and young adults (ages 14-21 years) drawn from the Philadelphia Neurodevelopmental Cohort, a prospective, population-based study. Participants were classified as cannabis Non-Users (n = 3,401), Occasional Users (twice per week or less; n = 940), or Frequent Users (>3 times per week; n = 227). Mixed-model analyses examined main effects of cannabis use and interactions between age and cannabis use on cognitive functioning. There was a significant interaction between cannabis group and age such that adolescent (but not young adult) Frequent Users performed worse than Non-Users on measures of executive control (p = .002). Earlier age of cannabis use was associated with worse performance in executive control in Occasional Users (p = .04). Unexpectedly, Occasional Users exhibited better executive control, memory, and social cognition than Non-Users (ps < .05). Although mild executive control deficits in adolescent frequent users and a relation between early cannabis initiation and cognitive performance are partially consistent with prior research, cognitive deficits were not found in other hypothesized domains in this community-based sample. Moreover, occasional cannabis users displayed equivalent or even slightly better executive control, social-cognitive, and memory abilities compared with nonusers, suggesting complex relationships between cannabis use and cognition in youth. Longitudinal studies with community samples are needed to identify variables affecting risk and resilience to cognitive deficits associated with cannabis. (PsycINFO Database Record

Evidence for the Risks and Consequences of Adolescent Cannabis Exposure

OBJECTIVE

This review of the scientific literature examines the potential adult sequelae of exposure to cannabis and related synthetic cannabinoids in adolescence. We examine the four neuropsychiatric outcomes that are likely most vulnerable to alteration by early cannabinoid use, as identified within both the clinical and preclinical research: cognition, emotional functioning, risk for psychosis, and addiction.

METHOD

A literature search was conducted through PubMed, PsychInfo, and Google Scholar with no publication date restrictions. The search terms used were "adolescent" and "adult," and either "cannabis," "marijuana," "delta-9-tetra-hydrocannabinol," or "cannabinoid," which was then crossed with one or more of the following terms: "deficit," "impairment," "alteration," "long-term," "persistent," "development," "maturation," and "pubescent."

RESULTS

The majority of the clinical and preclinical data point to a strong correlation between adolescent cannabinoid exposure and persistent, adverse neuropsychiatric outcomes in adulthood. Although the literature supports the hypothesis that adolescent cannabis use is connected to impaired cognition and mental health in adults, it does not conclusively demonstrate that cannabis consumption alone is sufficient to cause these deficits in humans. The animal literature, however, clearly indicates that adolescent-onset exposure to cannabinoids can catalyze molecular processes that lead to persistent functional deficits in adulthood, deficits that are not found to follow adult-onset exposure and that model some of the adverse outcomes reported in humans among adult populations of early-onset cannabis users.

CONCLUSION

Based on the data in the current literature, a strong association is found between early, frequent, and heavy adolescent cannabis exposure and poor cognitive and psychiatric outcomes in adulthood, yet definite conclusions cannot yet be made as to whether cannabis use alone has a negative impact on the human adolescent brain. Future research will require animal models and longitudinal studies to be carefully designed with a focus on integrating assessments of molecular, structural, and behavioral outcomes in order to elucidate the full range of potential adverse and long-term consequences of cannabinoid exposure in adolescence.

A longitudinal examination of the relationship between cannabis use and cognitive function in mid-life adults

BACKGROUND

The relationship between cannabis use and cognitive function in mid-life has rarely been examined despite verbal learning deficits in young adults.

METHOD

A longitudinal cohort study of 1,897 Australians recruited at 40-46 years of age and followed up 4 years (94%) and 8 years (87%) later. Random effects regression was used to assess within- and between-person associations between cannabis use and cognitive function across waves of data, and examine whether age-related changes in cognitive performance were modified by cannabis use. The first list of the California Verbal Learning Test (immediate and delayed recall), Symbol Digit Modality Test, Digit Backwards, simple and choice reaction time tasks, were administered at each wave. The Spot-the-Word test was used to assess premorbid verbal ability. Self-reported cannabis use in the past year (no use, < weekly use,≥weekly use) was assessed at each wave.

FINDINGS

Participants who used cannabis≥weekly had worse immediate recall (b=-0.68, p=0.014) and showed a trend toward worse delayed recall (b=-0.55, p=0.062) compared to non-users after adjusting for correlates of cannabis use and premorbid verbal ability. These effects were due to between-person differences. There were no significant within-person associations between cannabis use and recall, nor was there evidence of greater cognitive decline in cannabis users with age.

CONCLUSIONS

Mid-life cannabis users had poorer verbal recall than non-users, but this was not related to their current level of cannabis use, and cannabis use was not associated with accelerated cognitive decline.

The impact of ADHD persistence, recent cannabis use, and age of regular cannabis use onset on subcortical volume and cortical thickness in young adults

BACKGROUND

Both Attention Deficit Hyperactivity Disorder (ADHD) and chronic cannabis (CAN) use have been associated with brain structural abnormalities, although little is known about the effects of both in young adults.

METHODS

Participants included: those with a childhood diagnosis of ADHD who were CAN users (ADHD_CAN; n=37) and non-users (NU) (ADHD_NU; n=44) and a local normative comparison group (LNCG) who did (LNCG_CAN; n=18) and did not (LNCG_NU; n=21) use CAN regularly. Multiple regressions and MANCOVAs were used to examine the independent and interactive effects of a childhood ADHD diagnosis and CAN group status and age of onset (CUO) on subcortical volumes and cortical thickness.

RESULTS

After controlling for age, gender, total brain volume, nicotine use, and past-year binge drinking, childhood ADHD diagnosis did not predict brain structure; however, persistence of ADHD was associated with smaller left precentral/postcentral cortical thickness. Compared to all non-users, CAN users had decreased cortical thickness in right hemisphere superior frontal sulcus, anterior cingulate, and isthmus of cingulate gyrus regions and left hemisphere superior frontal sulcus and precentral gyrus regions. Early cannabis use age of onset (CUO) in those with ADHD predicted greater right hemisphere superior frontal and postcentral cortical thickness.

DISCUSSION

Young adults with persistent ADHD demonstrated brain structure abnormalities in regions underlying motor control, working memory and inhibitory control. Further, CAN use was linked with abnormal brain structure in regions with high concentrations of cannabinoid receptors. Additional large-scale longitudinal studies are needed to clarify how substance use impacts neurodevelopment in youth with and without ADHD.

The impact of initiation: Early onset marijuana smokers demonstrate altered Stroop performance and brain activation

Marijuana (MJ) use is on the rise, particularly among teens and emerging adults. This poses serious public health concern, given the potential deleterious effects of MJ on the developing brain. We examined 50 chronic MJ smokers divided into early onset (regular MJ use prior to age 16; n=24) and late onset (age 16 or later; n=26), and 34 healthy control participants (HCs). All completed a modified Stroop Color Word Test during fMRI. Results demonstrated that MJ smokers exhibited significantly poorer performance on the Interference subtest of the Stroop, as well as altered patterns of activation in the cingulate cortex relative to HCs. Further, early onset MJ smokers exhibited significantly poorer performance relative to both HCs and late onset smokers. Additionally, earlier age of MJ onset as well as increased frequency and magnitude (grams/week) of MJ use were predictive of poorer Stroop performance. fMRI results revealed that while late onset smokers demonstrated a more similar pattern of activation to the control group, a different pattern was evident in the early onset group. These findings underscore the importance of assessing age of onset and patterns of MJ use and support the need for widespread education and intervention efforts among youth.

Brain activation to negative stimuli mediates a relationship between adolescent marijuana use and later emotional functioning

This work investigated the impact of heavy marijuana use during adolescence on emotional functioning, as well as the brain functional mediators of this effect. Participants (n=40) were recruited from the Michigan Longitudinal Study (MLS). Data on marijuana use were collected prospectively beginning in childhood as part of the MLS. Participants were classified as heavy marijuana users (n=20) or controls with minimal marijuana use. Two facets of emotional functioning-negative emotionality and resiliency (a self-regulatory mechanism)-were assessed as part of the MLS at three time points: mean age 13.4, mean age 19.6, and mean age 23.1. Functional neuroimaging data during an emotion-arousal word task were collected at mean age 20.2. Negative emotionality decreased and resiliency increased across the three time points in controls but not heavy marijuana users. Compared with controls, heavy marijuana users had less activation to negative words in temporal, prefrontal, and occipital cortices, insula, and amygdala. Activation of dorsolateral prefrontal cortex to negative words mediated an association between marijuana group and later negative emotionality. Activation of the cuneus/lingual gyrus mediated an association between marijuana group and later resiliency. Results support growing evidence that heavy marijuana use during adolescence affects later emotional outcomes.

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.

Neuropsychological performance in adolescent marijuana users with co-occurring alcohol use: A three-year longitudinal study

OBJECTIVE

The effect of adolescent marijuana use on brain development remains unclear despite relaxing legal restrictions, decreased perceived harm, and increasing use rates among youth. The aim of this 3-year prospective study was to evaluate the long-term neurocognitive effects of adolescent marijuana use.

METHOD

Adolescent marijuana users with concomitant alcohol use (MJ + ALC, n = 49) and control teens with limited substance use histories (CON, n = 59) were given neuropsychological and substance use assessments at project baseline, when they were ages 16-19. They were then reassessed 18 and 36 months later. Changes in neuropsychological measures were evaluated with repeated measures analysis of covariance (ANCOVA), controlling for lifetime alcohol use, and examined the effects of group, time, and group by time interactions on cognitive functioning.

RESULTS

MJ + ALC users performed significantly worse than controls, across time points, in the domains of complex attention, memory, processing speed, and visuospatial functioning (ps <.05). Earlier age of marijuana use onset was associated with poorer processing speed and executive functioning by the 3-year follow-up (ps ≤.02).

CONCLUSIONS

Frequent marijuana use throughout adolescence and into young adulthood appeared linked to worsened cognitive performance. Earlier age of onset appears to be associated with poorer neurocognitive outcomes that emerge by young adulthood, providing further support for the notion that the brain may be uniquely sensitive to frequent marijuana exposure during the adolescent phase of neurodevelopment. Continued follow-up of adolescent marijuana users will determine the extent of neural recovery that may occur if use abates.

Long-term consequences of adolescent cannabinoid exposure in adult psychopathology

Marijuana is the most widely used illicit drug among adolescents and young adults. Unique cognitive, emotional, and social changes occur during this critical period of development from childhood into adulthood. The adolescent brain is in a state of transition and differs from the adult brain with respect to both anatomy (e.g., neuronal connections and morphology) and neurochemistry (e.g., dopamine, GABA, and glutamate). These changes are thought to support the emergence of adult cerebral processes and behaviors. The endocannabinoid system plays an important role in development by acting on synaptic plasticity, neuronal cell proliferation, migration, and differentiation. Delta-9-tetrahydrocanabinol (THC), the principal psychoactive component in marijuana, acts as a partial agonist of the cannabinoid type 1 receptor (CB1R). Thus, over-activation of the endocannabinoid system by chronic exposure to CB1R agonists (e.g., THC, CP-55,940, and WIN55,212-2) during adolescence can dramatically alter brain maturation and cause long-lasting neurobiological changes that ultimately affect the function and behavior of the adult brain. Indeed, emerging evidence from both human and animal studies demonstrates that early-onset marijuana use has long-lasting consequences on cognition; moreover, in humans, this use is associated with a two-fold increase in the risk of developing a psychotic disorder. Here, we review the relationship between cannabinoid exposure during adolescence and the increased risk of neuropsychiatric disorders, focusing on both clinical and animal studies.

Considering Cannabis: The Effects of Regular Cannabis Use on Neurocognition in Adolescents and Young Adults

Thirty-six percent of high school seniors have used cannabis in the past year, and an alarming 6.5% smoked cannabis daily, up from 2.4% in 1993 (Johnston et al., 2013). Adolescents and emerging adults are undergoing significant neurodevelopment and animal studies suggest they may be particularly vulnerable to negative drug effects. In this review, we will provide a detailed overview of studies outlining the effects of regular (at least weekly) cannabis use on neurocognition, including studies outlining cognitive, structural and functional findings. We will also explore the public health impact of this research.