A Northwestern University study revealed heavy use of cannabis or marijuana during teenage years correlates to abnormality in the shape of hippocampus, thus leading to poor long-term memory in adulthood.
The study involved 97 participants—grouped further into young adult subjects with no history of cannabis use, young adult subjects with history of abusing cannabis as teens, schizophrenia subjects with no history of substance abuse, and schizophrenia subjects with history of cannabis abuse as teens.
In order to assess the ability of participants to encode, store, and recall memory, the researchers subjected them under a narrative memory test.
Test results revealed participants who had history of cannabis abuse have poorer long-term memory performance than their counterparts who never abused cannabis.
Using brain mapping tools, the researchers have further identified brain abnormalities among participants who abused cannabis during their teenage years.
“Advanced brain mapping tools allowed us to examine detailed and sometimes subtle changes in small brain structures, including the hippocampus,” said Lei Wang, senior author and an assistant professor of psychiatry and behavioural sciences at Feinberg School of Medicine, Northwestern Univeristy.
According to the researchers, longer use and abuse of cannabis might lead to a more abnormally shaped hippocampus. This abnormality is likely to reflect damage to the brain component and could also include damages in neurons, axons, or other supporting structures.
The hippocampus is a major component of the brain important to long-term or episodic memory. It plays a critical role in the ability of individuals to remember autobiographical experiences or life events.
This same team of researchers from Northwestern Univeirsty has also conducted a similar study revealing how cannabis abuse causes poor short-term memory and working memory performance, as well as abnormalities in brain structures in the sub-cortex including the striatum, globus pallidus, and thalamus.
“Both our recent studies link the chronic use of marijuana during adolescence to these differences in the shape of brain regions that are critical to memory and that appear to last for at least a few years after people stop using it,” said lead author Matthew Smith, assistant professor of psychiatry and behavioral sciences at the Feinberg School of Medicine.
Further details of the research are found in the article “Cannabis-related episodic memory deficits and hippocampal morphological differences in healthy individuals and schizophrenia subjects” published in 2015 in the journal Hippocampus. Hans C. Breiter is also a senior author while Derin J. Cobia, James L. Reilly, Andrea G. Roberts, and Kathryn I. Alpert are coauthors.