Chronic cannabis users (mean 16.4 years near-daily use) made more errors on color-incongruent Stroop trials and showed altered brain electrical activity during conflict resolution, with earlier onset predicting worse performance.
Read this if you are interested in how long-term cannabis use affects the ability to resolve conflicting information.
More errors on conflict trials; earlier onset predicted worse performance
What the researchers found
Twenty-one chronic cannabis users (mean 16.4 years near-daily use, unintoxicated) and 19 controls completed a Stroop color-naming task while ERPs were recorded.
Cannabis users made significantly more errors specifically on incongruent trials (where the word meaning conflicts with the ink color, like "RED" written in blue). Performance on congruent and neutral trials was normal.
An earlier age of onset of regular cannabis use predicted worse incongruent trial performance.
ERP analysis showed altered expression of a late sustained potential related to conflict resolution. Cannabis users showed opposite patterns of brain activity between trial types at certain electrode sites, along with altered relationships between brain activity and behavioral performance not seen in controls.
Why it matters
Conflict resolution is essential for self-regulation, decision-making, and behavior control. Impaired conflict processing could contribute to difficulty controlling substance use and making decisions that require overriding automatic responses.
The numbers in context
21 users (mean 16.4 years near-daily use), 19 controls. Increased errors on incongruent trials only. Earlier age of onset predicted worse performance. Altered late sustained potential in users.
How the study worked
Cross-sectional ERP study comparing 21 chronic cannabis users (unintoxicated, mean 16.4 years near-daily use) with 19 non-using controls on a discrete-trial Stroop color-naming task.
What this study cannot tell us
Cross-sectional design cannot establish causation. Very heavy use sample may not generalize. Brain activity differences are correlational and could reflect pre-existing differences. Unintoxicated state does not rule out residual THC effects.
How to read the evidence
Cross-sectional ERP study with appropriate methodology but small sample of very heavy users and inability to establish causation.
When this study was published
Published in 2010. Executive function deficits in chronic cannabis users have been consistently reported in subsequent research.
The bigger picture
Along with the companion study on memory (RTHC-00399), this research showed that chronic cannabis use is associated with altered brain processes for both memory encoding and cognitive conflict resolution, two fundamental cognitive operations.
Questions still open
- Does impaired conflict resolution contribute to continued cannabis use? Would abstinence restore normal Stroop performance and brain responses? Is early-onset use specifically harmful to conflict resolution development?
Common questions
What is the Stroop test?
Why does earlier onset matter?
Read the original research
Chronic cannabis users show altered neurophysiological functioning on Stroop task conflict resolution.
Psychopharmacology, 212(4), 613-24
Citation
Battisti, Robert A; Roodenrys, Steven; Johnstone, Stuart J; Pesa, Nicole; Hermens, Daniel F; Solowij, Nadia. (2010). Chronic cannabis users show altered neurophysiological functioning on Stroop task conflict resolution.. Psychopharmacology, 212(4), 613-24. https://doi.org/10.1007/s00213-010-1988-3
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