People with a past cannabis use disorder showed distinct hippocampal shape changes whether they had schizophrenia or not, with healthy cannabis users' changes linked to memory problems and schizophrenia cannabis users' changes linked to longer use duration.
Read this if you are interested in how cannabis affects brain structure differently in people with and without mental illness.
Different hippocampal shape changes in healthy vs. schizophrenia cannabis users
What the researchers found
Researchers compared hippocampal shape in four groups: healthy controls (n=44), healthy controls with past cannabis use disorder (n=10), schizophrenia without substance history (n=28), and schizophrenia with past cannabis use disorder (n=15).
Both cannabis-using groups showed distinct hippocampal shape differences from their respective non-using counterparts, but the patterns differed. In healthy cannabis users, shape changes correlated with poorer episodic memory performance. In schizophrenia cannabis users, shape changes correlated with longer duration of cannabis use and shorter duration of remission.
This suggests cannabis-related hippocampal changes have different functional consequences depending on whether someone has schizophrenia.
Why it matters
The hippocampus is central to memory formation and is affected by both cannabis and schizophrenia. Finding that cannabis-related hippocampal changes differ between healthy and schizophrenia populations suggests the underlying neurobiology differs.
The numbers in context
44 healthy controls; 10 healthy with past CUD; 28 schizophrenia without substance use; 15 schizophrenia with past CUD; distinct hippocampal shape patterns in each cannabis-using group
How the study worked
Cross-sectional MRI study with four demographically matched groups. Large-deformation, high-dimensional brain mapping produced surface-based hippocampal representations. Correlated morphological differences with episodic memory and cannabis use history.
What this study cannot tell us
Small groups (especially n=10 for healthy cannabis users). Past, not current, cannabis use studied. Cross-sectional design cannot determine whether hippocampal differences preceded or followed cannabis use. Shape changes do not reveal cellular mechanisms.
How to read the evidence
Sophisticated neuroimaging with four well-matched groups, but small sample sizes limit statistical power and generalizability.
When this study was published
Published in 2015. Brain imaging of cannabis effects has become more refined.
The bigger picture
Cannabis effects on the brain may not be uniform across populations. People with schizophrenia may be uniquely vulnerable to certain cannabis-related brain changes, which could explain why cannabis use is particularly harmful in this population.
Questions still open
- Do hippocampal shape changes reverse with prolonged abstinence? Are these changes markers of vulnerability or consequences of use? Would longer-duration cannabis use in healthy people eventually produce the schizophrenia-like pattern?
Common questions
Does cannabis change the shape of the hippocampus?
Does cannabis affect memory through hippocampal changes?
Read the original research
Cannabis-related episodic memory deficits and hippocampal morphological differences in healthy individuals and schizophrenia subjects.
Hippocampus, 25(9), 1042-51
Citation
Smith, Matthew J; Cobia, Derin J; Reilly, James L; Gilman, Jodi M; Roberts, Andrea G; Alpert, Kathryn I; Wang, Lei; Breiter, Hans C; Csernansky, John G. (2015). Cannabis-related episodic memory deficits and hippocampal morphological differences in healthy individuals and schizophrenia subjects.. Hippocampus, 25(9), 1042-51. https://doi.org/10.1002/hipo.22427
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