Scientists Discover Why Marijuana Impairs Short-Term Memory

Researchers from the University of California, San Diego have published the results of a study examining the effects of marijuana on the brain. The scientists have identified why smoking marijuana leads to a decline in working (short-term) memory.

Cannabis Disrupts Concentration

The specialists conducted two separate experiments, each involving 24 healthy volunteers who had previously tried marijuana. The average age of the participants was 23 years old. In the first test, volunteers were divided into two groups: one received capsules containing 15 mg of THC, while the other received a placebo. In the second experiment, participants were split into three groups: the first group received 15 mg of THC, the second received 7.5 mg of THC, and the third received a placebo. Both the researchers and the participants were unaware of which capsules contained THC or placebo.

Between two and 3.7 hours after taking the capsules, the volunteers completed a task designed to assess working memory performance. They were asked to recall the locations of colored squares on a grid. The university researchers found that in both experiments, people who took 15 mg of THC made significantly more mistakes than those who received a placebo. However, the test results of volunteers who took 7.5 mg of THC were nearly identical to those of the placebo group.

Additionally, the scientists observed that participants who consumed 15 mg of THC:

• Focused on topics unrelated to the task and became distracted by unrelated thoughts;
• Had difficulty concentrating on a single subject;
• Were unable to accurately assess how well they were performing the test.

The Effects of Marijuana Resemble Those of Alcohol

According to lead researcher Adam Kirsten, the decline in working memory is due to THC disrupting the function of the dorsolateral prefrontal cortex (DLPFC). This area of the brain plays a crucial role in decision-making and manages the monitoring and manipulation of information, which is essential for working memory. The DLPFC contains a high concentration of cannabinoid receptors, making it especially sensitive to the effects of marijuana.

When the DLPFC is impaired, it results in distractibility and detachment, which is why THC reduces the effectiveness of cognitive task performance. Kirsten believes that the way marijuana affects working memory is similar to the effects of alcohol and nicotine cravings. People who are intoxicated or smokers deprived of cigarettes also struggle to concentrate and focus on specific tasks.