THC reduced the brain's error-detection signal in healthy volunteers | Research

The takeaway

After inhaling THC vapor, healthy volunteers showed a significantly reduced error-related negativity (ERN) brain signal, indicating impaired performance monitoring.

Read this if you want to understand how THC affects the brain's ability to detect its own mistakes.

First study to show cannabinoid effects on error-related negativity

What the researchers found

Ten healthy volunteers completed a speeded Flankers task (a test of accuracy under time pressure) after receiving THC or placebo vapor in a double-blind crossover design. EEG recordings showed the error-related negativity (ERN), a brain signal that fires immediately after making a mistake, was significantly reduced after THC.

Despite this reduced error-detection signal, behavioral performance on the task was not significantly different between THC and placebo conditions. This disconnect suggested THC impaired the brain's internal monitoring system without immediately degrading task performance in this simple paradigm.

This was the first study to directly demonstrate cannabinoid effects on the ERN.

Why it matters

Performance monitoring is essential for catching and correcting mistakes. A reduced ERN means the brain is less aware of its own errors, which could have implications for driving, complex decision-making, and other tasks where error detection matters.

The numbers in context

10 healthy volunteers. ERN was significantly reduced after THC compared to placebo. Behavioral accuracy on the Flankers task was not significantly different between conditions.

How the study worked

Double-blind, randomized, placebo-controlled crossover design. 10 healthy volunteers inhaled THC or placebo vapor. EEG was recorded during a speeded Flankers choice-reaction-time task. Error-related negativity was measured on error trials.

What this study cannot tell us

Very small sample size (10 volunteers). Single acute dose design. The Flankers task was not optimized to detect behavioral effects. The disconnect between ERN reduction and preserved behavior might not hold in more demanding real-world tasks.

How to read the evidence

Small RCT with 10 participants. First demonstration of its kind but underpowered for definitive conclusions.

When this study was published

Published in 2011. Subsequent studies have replicated and extended findings on cannabis effects on performance monitoring.

The bigger picture

Reduced ERN is also seen in schizophrenia and other psychiatric conditions. This parallel between THC effects and psychosis-related brain changes added to the evidence linking cannabinoid system disruption to psychosis-relevant cognitive changes.

Questions still open

Does chronic cannabis use permanently reduce the ERN? Would more complex tasks reveal behavioral consequences of impaired performance monitoring? Is the reduced ERN related to the subjective "not caring about mistakes" experience reported by cannabis users?

Common questions

Does THC make you worse at noticing your mistakes?

This study found THC reduced the brain's automatic error-detection signal. Participants did not perform worse on a simple task, but the reduced internal monitoring could matter for complex, high-stakes activities where catching errors quickly is important.

What is the error-related negativity?

The ERN is a brain wave that fires within 100 milliseconds of making an error, before you are even consciously aware of the mistake. It reflects the brain's automatic quality-control system. A smaller ERN means this system is less active.

Read the original research

Acute effects of delta-9-tetrahydrocannabinol on performance monitoring in healthy volunteers.

Frontiers in behavioral neuroscience, 5, 59

View on PubMed ↗Publisher’s paper ↗

Citation

Spronk, Desirée; Dumont, Glenn J H; Verkes, Robbert J; de Bruijn, Ellen R A. (2011). Acute effects of delta-9-tetrahydrocannabinol on performance monitoring in healthy volunteers.. Frontiers in behavioral neuroscience, 5, 59. https://doi.org/10.3389/fnbeh.2011.00059