marijuana

Study: Marijuana Use Affects Brain Structure, Long-Term Memory

Daily, heavy use of marijuana as a teenager changes the physical structure of the brain and is linked to long-term memory problems later in life, according to a new study.

Previous studies have observed an association between marijuana use and memory impairment associated with physical abnormalities of the hippocampus, a region of the brain important to long-term, episodic memory.
________________________________________________________________________________________________________________________________________________________________

RELATED CONTENT
Marijuana Use Can Change Brain's Physical Structure
Even Casual Marijuana Use Changes the Brain
________________________________________________________________________________________________________________________________________________________________

In order to further explore the relationship between these marijuana-related changes to the hippocampus and memory impairments, researchers analyzed data from 97 participants, including:

  • 44 controls.
  • 10 participants who reported previous marijuana use.
  • 28 patients with schizophrenia.
  • 15 patients with schizophrenia and previous marijuana use.

Participants with a history of marijuana use reported daily, chronic use for an average of 3 years, beginning at either age 16 or 17 years old. They had been marijuana-free for an average of 2 years.

Researchers used high dimensional brain mapping and MRI to compared the shape of participants’ hippocampus. Memory was tested using a narrative memory test, which asked participants to recall as much of a 1-minute story as possible, 20-30 minutes after hearing it.

Researchers found that the length of participants' history of marijuana use was proportionally associated to the level of abnormality of the shape of their hippocampus. These structural changes were associated with an 18% worse performance on memory tests in healthy participants with a history of marijuana use and 26% worse performance in participants with schizophrenia and a history of marijuana use.

The researchers noted, however, that the current study is unable to conclusively show a correlation between marijuana use, physical brain changes, and memory impairment.

"Although the results may be compatible with a causal hypothesis, we must consider that the observed cannabis-related shape differences in the hippocampus could also be explained as biomarkers of a neurobiological susceptibility to poor memory or the effects of cannabis.”

—Michael Potts

Reference:

1. Smith MJ, Cobia DJ, Reilly JL, et al. Cannabis-related episodic memory deficits and hippocampal morphological differences in healthy individuals and schizophrenia subjects. 2015 March [epub ahead of print]. DOI: 10.1002/hipo.2242.