Young Adults Exposed to Cannabis Before Birth Showed Altered Brain Activity During Memory Tasks | Research

The takeaway

fMRI scans of 18-22 year olds from a 20-year longitudinal study found that prenatal marijuana exposure was associated with altered brain activation patterns during visuospatial working memory, even though task performance was similar to non-exposed participants.

Read this if you want to understand the long-term brain effects of prenatal cannabis exposure.

Altered brain activation patterns detected 18-22 years after prenatal cannabis exposure

What the researchers found

Researchers scanned 31 participants from the Ottawa Prenatal Prospective Study (16 prenatally exposed to cannabis, 15 non-exposed) at age 18-22 using fMRI during a visuospatial working memory task. This longitudinal study had tracked participants for over 20 years, providing detailed prenatal drug history and controlling for other exposures.

Performance on the memory task did not significantly differ between exposed and non-exposed groups. However, as the amount of prenatal marijuana exposure increased, there was significantly more neural activity in the left inferior and middle frontal gyri, left parahippocampal gyrus, left middle occipital gyrus, and left cerebellum, and significantly less activity in right inferior and middle frontal gyri.

The pattern suggests prenatal exposure alters the neural circuits used during memory processing in adulthood, even when behavioral performance appears intact.

Why it matters

This is one of the few studies to examine prenatal cannabis exposure effects into young adulthood using brain imaging. The finding that neural functioning is altered 18-22 years after prenatal exposure, even without behavioral deficits, suggests long-lasting effects on brain development that may become apparent under more demanding conditions.

The numbers in context

31 participants from OPPS (16 exposed, 15 non-exposed). Age 18-22. 20+ years of longitudinal data. No performance differences. Increased left-hemisphere activation and decreased right-hemisphere activation associated with more prenatal exposure.

How the study worked

Longitudinal cohort study from the Ottawa Prenatal Prospective Study (OPPS). 31 participants (16 prenatally exposed, 15 non-exposed) aged 18-22. fMRI during visuospatial 2-back working memory task. Multiple regression analyses controlled for potentially confounding drug exposure variables using 20 years of collected data.

What this study cannot tell us

Small sample size (31 participants). Cannot rule out all confounding factors despite extensive controls. The 2-back task may not be challenging enough to reveal behavioral deficits. Prenatal exposure was self-reported by mothers. Results may not generalize to all levels of prenatal exposure.

How to read the evidence

Longitudinal cohort study with 20+ years of data and neuroimaging. Unique design strength but small sample limits statistical power.

When this study was published

Published in 2006. The OPPS cohort has continued to be studied, providing some of the longest follow-up data on prenatal cannabis exposure effects.

The bigger picture

The OPPS is one of the longest-running studies of prenatal cannabis exposure. The finding of altered neural activity without performance deficits parallels the compensatory activation pattern seen in adult cannabis users, suggesting prenatal exposure may produce lasting neural adaptations that are sub-clinical but detectable with imaging.

Questions still open

Would more demanding cognitive tasks reveal behavioral differences between exposed and non-exposed groups? Do the altered brain activation patterns have functional consequences in real-world situations?

Common questions

Does using marijuana during pregnancy affect the child's brain long-term?

This study found altered brain activation patterns in 18-22 year olds who were exposed to marijuana before birth, even though their memory task performance was normal. This suggests prenatal exposure may produce lasting changes in how the brain processes information.

Did prenatally exposed children have worse memory?

Not on the task tested. Both groups performed similarly on a visuospatial working memory task. However, the exposed group used different brain regions to achieve the same performance, suggesting the brain may compensate for exposure-related changes.

Read the original research

Effects of prenatal marijuana on visuospatial working memory: an fMRI study in young adults.

Neurotoxicology and teratology, 28(2), 286-95

View on PubMed ↗

Citation

Smith, Andra M; Fried, Peter A; Hogan, Matthew J; Cameron, Ian. (2006). Effects of prenatal marijuana on visuospatial working memory: an fMRI study in young adults.. Neurotoxicology and teratology, 28(2), 286-95.