Tags: Cannabis; Hippocampus; Segmentation; Longitudinal; Memory

 

Thumbnail: This study looks at long-term effects of cannabis use on the hippocampus. It uses data from a previous study to expand on those findings and analyzes subfields of the hippocampus separately from the organ as a whole. The results show that long-term cannabis use does not lead to changes in the volume of the hippocampus as a whole, but may lead to differences in the development of subfields within the hippocampus.

 

The problem: The psychoactive effects of cannabis have been extensively documented, and cannabis use has been linked to a number of psychiatric conditions. Decreased grey matter in the hippocampus has also been associated with many of these same conditions but there have been few studies looking at the effects of long-term cannabis usage on the hippocampus.

 

The study: This study looked at the long-term effects of cannabis usage on the hippocampus. It uses data from a previously published study, which evaluated the differences in hippocampus between cannabis users and healthy controls by comparing results of Cannabis Usage and Disorder Identification Test (CUDIT) (to establish usage habits) and structural MRI scans (to examine the hippocampus). Over a period of 3 years, the scans compared the volume of the hippocampus between these two groups. This study it provides a more thorough evaluation than previous published because it evaluates different subfields of the organ separately. The study evaluated 23 healthy controls and 20 heavy cannabis users.

 

Main Points:

• Overall, this study agrees with the previous findings: that there is no significant difference in the hippocampus volumes between cannabis users and healthy controls, when considering the hippocampus as a whole

• While analysis of most subfields was the same between the two groups, this study find differences in certain subfields of the hippocampus:

  • There was a greater increase in the volume of the right hemispheric parasubiculum and fimbria in cannabis users.

  • There was also an increase in the volumes of the CA3 in both hemispheres for cannabis users.

• This study found that continued cannabis use did not result in hippocampus changes that could be distinguished from non-users.

 

Conclusions: Long-term cannabis usage does not lead to significant changes in the size of the hippocampus, as a whole. However, this study suggests that certain subsections of the hippocampus may develop differently as a result of cannabis usage.

 

Why this is a good study:

• The study deliberately excluded participants who had very high alcohol usage, other substance dependencies, or a history of psychiatric disorders, which reduces the potential influence of other confounding factors.

• It followed the same subjects throughout the study period, which eliminates some variation which can arise when comparing different individuals

 

Why this isn’t a perfect study:

• The sample size was relatively small, however this is an innate challenge of any longitudinal study

• The participants in this study were aged 18-25 years old--an age at which people are still undergoing neuroanatomic development, which could account for some of the changes observed

 

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What this study adds:

• This study is the first to look at the effects of cannabis on subfields of the hippocampus and evaluate them over time

• It shows that there may be differences at these sub-levels which are not apparent when evaluating the hippocampus as a whole

 

What it doesn’t:

• This study does not tell us how cannabis use may effect the hippocampus in users older than 25 or how use for more than 3 years may affect brain volume.

 

Funder:  No agency funding was reported

 

Author conflicts:  None