Schizophrenia patients who previously used cannabis showed different brain activation patterns during cognitive tasks | Research

The takeaway

Schizophrenia patients with previous cannabis use showed better brain activation during cognitive tasks and less default-mode network activity during rest, compared to patients who never used cannabis.

Read this if you want to understand the brain differences between schizophrenia patients who have and have not used cannabis.

Cannabis-using patients better at "switching on" for cognitive tasks

What the researchers found

Twenty-six schizophrenia patients were divided into previous cannabis users and never-users and compared during an auditory attention task (dichotic listening) using fMRI. During the cognitive task, previous cannabis users showed remaining brain activations in effort-mode regions that were not seen in the no-cannabis group.

Conversely, during rest periods (task-absent condition), the no-cannabis group showed remaining activation in default-mode regions not seen in the cannabis group. This meant cannabis-using patients were better at "switching on" during tasks and "switching off" during rest.

The authors interpreted this as cannabis-using schizophrenia patients having lower neurocognitive vulnerability, consistent with previous behavioral studies showing better cognitive performance in cannabis-using patients.

Why it matters

The finding that cannabis-using schizophrenia patients showed more normal brain activation patterns supported the hypothesis that they represent a distinct subgroup with lower inherent cognitive vulnerability who may have been pushed into psychosis by cannabis rather than by severe underlying neurodevelopmental problems.

The numbers in context

26 schizophrenia patients. Cannabis users: better task-related activation, less default-mode activation at rest. No-cannabis group: less task activation, more default-mode activation at rest.

How the study worked

Cross-sectional fMRI study of 26 schizophrenia patients (DSM-IV and ICD-10 criteria) grouped by cannabis use history. Auditory dichotic listening task with instructions to focus attention on right or left ear. Brain activation compared during task-present and task-absent conditions.

What this study cannot tell us

Small sample (26 patients). Cross-sectional design cannot determine whether cognitive differences predate or result from cannabis use. Previous cannabis use was self-reported. No healthy control group for comparison. Cannot rule out other substance use effects.

How to read the evidence

Small cross-sectional fMRI study without healthy controls. Preliminary but adds neuroimaging support to behavioral findings of better cognition in cannabis-using psychosis patients.

When this study was published

Published in 2012. The cognitive paradox in cannabis-using schizophrenia patients continues to be studied.

The bigger picture

This aligned with the "two-hit" model of psychosis: some patients develop schizophrenia primarily from genetic/neurodevelopmental vulnerability (and show worse cognition), while others with lower vulnerability are pushed into psychosis by environmental triggers like cannabis (and show better baseline cognition).

Questions still open

Do cannabis-using schizophrenia patients have genuinely better long-term cognitive outcomes? Would removing cannabis trigger lead to faster recovery in this subgroup? Can brain activation patterns predict treatment response?

Common questions

Why would cannabis users with schizophrenia have better brain function?

The leading explanation is not that cannabis improved their brains, but that they started with better cognitive function. Cannabis may trigger psychosis in people who otherwise have healthier brains, while people with worse underlying brain function develop psychosis without needing cannabis as a trigger.

Does this mean cannabis protects the brain?

No. The interpretation is that cannabis-using patients had higher baseline cognitive function before their psychosis. Cannabis likely contributed to their psychosis onset, but their underlying neurocognitive health was better than patients who developed psychosis without cannabis exposure.

Read the original research

An fMRI Study of Neuronal Activation in Schizophrenia Patients with and without Previous Cannabis Use.

Frontiers in psychiatry, 3, 94

View on PubMed ↗Publisher’s paper ↗

Citation

Løberg, Else-Marie; Nygård, Merethe; Berle, Jan Øystein; Johnsen, Erik; Kroken, Rune A; Jørgensen, Hugo A; Hugdahl, Kenneth. (2012). An fMRI Study of Neuronal Activation in Schizophrenia Patients with and without Previous Cannabis Use.. Frontiers in psychiatry, 3, 94. https://doi.org/10.3389/fpsyt.2012.00094