Research Items (4)
- Nov 2018
Whether the effects of cannabis use on brain function persist or recover following abstinence remains unclear. Therefore, using meta-analytic techniques, we examined whether functional alterations measured using fMRI persist in cannabis users abstinent for over 25 days (or 600 h) as evidence suggests that the effects on cognitive performance no longer persist beyond this period. Systematic literature search identified 20 studies, of which, 12 examined current cannabis users (CCU) (361 CCU versus 394 non-cannabis using controls (NU)) and 3 examined abstinent cannabis users (ACU) in 5 separate comparisons (98 ACU versus 106 NU). Studies in ACU were carried out in adolescents and suggest significantly greater activation in components of the central executive and default mode networks in adolescent ACU compared to NU. While this evidence is to be interpreted with caution because studies were carried out in overlapping samples, they indicate a pressing need for independent confirmation whether certain neurofunctional alterations in adolescent cannabis users may persist even after cannabis and its metabolites are likely to have left their bodies.
Background Global neurocognitive impairments are a central feature of psychosis. Deficits in verbal memory in particular are the most consistently reported of these impairments from the first-episode of psychosis (FEP). Neuroimaging studies in psychosis have largely identified reductions in neural activation during various memory and learning related tasks, particularly in the medial temporal lobe, compared to healthy controls. Tetrahydrocannabinol (THC) and cannabidiol (CBD), both components of the cannabis plant that act through the endocannabinoid (eCB) system in the brain, have been found to induce direct and opposite neural effects during similar tasks in healthy samples, when compared to each other. Additionally, CBD has been shown to have antipsychotic properties, and may suppress THC induced psychotic symptoms and their directly associated functional abnormalities in healthy individuals. Thus far, the effects of CBD on the neural substrates implicated in memory and learning, and those underlying psychotic symptoms in FEP cohorts is unknown. Methods 17 FEP patients were initially recruited to the study. A double-blind, randomized, placebo controlled, repeated measures, within subject cross over design, with at least a one-week washout period between scans was employed. Participants were given identical capsules of either CBD (600mg), or placebo (PLB), then scanned using a block design fMRI paradigm, while performing a verbal paired associate learning task. 13 participants completed scanning, and were included in the analysis of the data. An ROI mask of the hippocampus, striatum, and parahippocampal gyrus was used in the data analysis, and all results were thresholded for less than one false positive over the whole map. Results A CBD related decrease in activity was observed in the left hippocampus (p = 0.0024) and the right parahippocampal gyrus (p = 0.0024) during the recall condition, within the FEP group. No significant differences between PLB and CBD functional activity were observed during the encoding condition. No significant differences were observed between FEP participant performances on the CBD and PLB study days. Discussion These findings provide robust evidence of the modulatory effect of an acute dose of CBD on the neural substrates underlying learning and memory, supporting a role for the eCB system in the abnormalities observed in psychosis, and its potential as a target for treatment.
- Apr 2018
- Schizophrenia International Research Society 2018 Congress
Background Long-term use of cannabis has long been associated with changes in cognition, including memory and learning, particularly verbal learning in man. However, evidence regarding the neurobiological underpinnings of impairments in memory following long-term cannabis use has not been consistent. Furthermore, to our knowledge none of the studies published to date have specifically investigated whether brain function differed between cannabis users and non-users while learning new information as estimated over repeated trials. Therefore, we aimed to investigate this. Methods Twenty-one predominantly cannabis users (CU) who started using cannabis during adolescence and 21 healthy non-using controls (NU), completed a block design verbal paired associates learning task whilst undergoing functional Magnetic Resonance Imaging. The task required participants to learn and recall a set of word-pairs over 4 repeated trials. We examined the interaction between repetition and group (CU vs NU) on brain activation during encoding and recall condition using non-parametric repeated measures analysis of variance. Results There was no significant difference in total recall score between CU and NU. However, there was a significant effect of repetition (p<0.001) on recall score, suggesting that there was a significant improvement in recall score over repeated trials across the two groups of participants. Furthermore, there was a significant interaction between repetition and group on recall score such that the change in recall score over repeated trials significantly differed (p =0.032) between the CU and NU groups. This was associated with a significant interaction (p =0.009) between group and repetition on activation in the midbrain bilaterally, extending to the, parahippocampus, caudate and cingulate gyrus during the encoding condition. There was greater engagement of these regions in CU than in NU over repeated encoding trials. Discussion These results suggest that verbal learning is slower and more effortful requiring greater engagement of critical brain areas involved in learning in cannabis users compared to non-users.
- Mar 2018
While numerous studies have investigated the residual effects of cannabis use on human brain function, results of these studies have been inconsistent. Using meta-analytic approaches we summarize the effects of prolonged cannabis exposure on human brain function as measured using task-based functional MRI (fMRI) across studies employing a range of cognitive activation tasks comparing regular cannabis users with non-users. Separate meta-analyses were carried out for studies investigating adult and adolescent cannabis users. Systematic literature search identified 20 manuscripts (13 adult and 7 adolescent studies) meeting study inclusion criteria. Adult analyses compared 530 cannabis users to 580 healthy controls while adolescent analyses compared 219 cannabis users to 224 healthy controls. In adult cannabis users brain activation was increased in the superior and posterior transverse temporal and inferior frontal gyri and decreased in the striate area, insula and middle temporal gyrus. In adolescent cannabis users, activation was increased in the inferior parietal gyrus and putamen compared to healthy controls. Functional alteration in these areas may reflect compensatory neuroadaptive changes in cannabis users.