Full Breakdown
Longitudinal fMRI Study of Reward Anticipation in Weekly Cannabis Users
6/21/2026, 11:51:53 PM
Design and Participants
The CannTeen project enrolled 140 individuals from Greater London between November 2017 and April 2021. Participants were divided equally into four groups: adolescent (16–17 years) and adult (26–29 years) weekly cannabis users (PWUC) and matched non-using controls (35 per group). PWUC met a criterion of at least one use per week over the prior three months; controls reported ten or fewer lifetime uses and, for adults, no frequent use before age 18. All participants gave written informed consent.
Imaging and MID Task
Scanning used a 3.0 T Siemens Verio system with multiband T2* echo-planar imaging and T1-weighted MPRAGE sequences, identical at baseline and 12-month follow-up. Reward anticipation was probed with the Monetary Incentive Delay (MID) task, which presented win and neutral trials; mean reaction time for each trial type served as the primary behavioural metric.
Statistical Approach
The study was powered (? = 0.05, 80 % power) to detect a small-to-medium interaction effect (f = 0.14) between Time (baseline vs. follow-up) and User-Group. Whole-brain analyses employed FSL FEAT with a cluster-defining threshold of Z = 3.1 and family-wise corrected p = 0.05. Region-of-interest (ROI) analyses focused on bilateral ventral striatum, right thalamus, right anterior insula, and right supplementary motor area. ROI beta values entered linear mixed-effects models with fixed effects for Time, User-Group, Age-Group, and their interactions, adjusting for baseline risk-taking, depressive symptoms (BDI), and weekly cigarette use.
Data Management
Participants provided saliva drug screens and breath-alcohol tests to confirm >=12-hour cannabis and >=48-hour other-drug abstinence before each session. Missing behavioural entries for a few participants were imputed using the most recent valid session values. Test-retest reliability of ROI activation was assessed via intraclass correlation coefficients (ICC) using a two-way mixed-effects model.
Official Oversight
The investigation received ethical approval from the University College London ethics committee (project ID 5929/003) and was pre-registered on the Open Science Framework. The authors affirmed compliance with the Declaration of Helsinki and detailed the methodological rigor of imaging and statistical pipelines.
Conflicting Reports
The source material does not disclose outcome findings, leaving the direction of longitudinal changes in reward-related brain activity unspecified. Although most participants completed the follow-up scan within the intended window, the actual mean interval was 1.07 years (range 0.83–1.76 years), reflecting a deviation caused by COVID-19 lockdowns.
Verbatim Quotes
- “The study was conducted in line with the Declaration of Helsinki and was approved by the University College London (UCL) ethics committee (project ID 5929/003).” — Study Authors
- “The first CannTeen study session took place on the 1st of November 2017, and the final one on the 16th of April 2021.” — Study Timeline
- “Reward anticipation was examined with the win anticipation > neutral anticipation contrast, which is the most commonly analysed contrast in studies using the MID task [39].” — Study Authors
- “Analyses were pre-registered to the Open Science Framework [22].” — Study Authors
