Several studies, including two large longitudinal studies, suggest that marijuana use can cause functional impairment in cognitive abilities but that the degree and/or duration of the impairment depends on the age when a person began using and how much and how long he or she used. 41
Marijuana, Memory, and the Hippocampus
Also, the ability to draw definitive conclusions about marijuana’s long-term impact on the human brain from past studies is often limited by the fact that study participants use multiple substances, and there is often limited data about the participants’ health or mental functioning prior to the study. Over the next decade, the National Institutes of Health is funding the Adolescent Brain Cognitive Development (ABCD) study—a major longitudinal study that will track a large sample of young Americans from late childhood (before first use of drugs) to early adulthood. The study will use neuroimaging and other advanced tools to clarify precisely how and to what extent marijuana and other substances, alone and in combination, affect adolescent brain development.
Distribution of cannabinoid receptors in the rat brain. Brain image reveals high levels (shown in orange and yellow) of cannabinoid receptors in many areas, including the cortex, hippocampus, cerebellum, and nucleus accumbens (ventral striatum).
They found that HU210 seemed to induce new brain cell growth, just as some antidepressant drugs do, they report in the Journal of Clinical Investigation 1 . This suggests that they could potentially be used to reduce anxiety and depression, Zhang says. He adds that the research might help to create new cannabinoid-based treatments.
Neuropsychologist Xia Zhang and a team of researchers based at the University of Saskatchewan in Saskatoon, Canada, aimed to find out just how marijuana-like drugs, known collectively as cannabinoids, act on the brain.
He says his group’s next studies will examine this more unpleasant side of the drug. Other addiction researchers will be keenly interested in the results, because this cannibinoid acts so differently on the hippocampus than other drugs.
“It makes marijuana look more like an antidepressant and less like a drug of abuse. Amelia Eisch , University of Texas Southwestern Medical Centre, Dallas”
Eisch adds that much more work must be done before scientists can reach any definitive conclusions about the benefits and costs of marijuana. First and foremost, researchers need to establish that THC has the same positive effects as the synthetic HU210. Then they must develop more sophisticated experiments to firm up the correlation between neuron growth in the hippocampus and emotional balance.
Many drugs, such as heroin, cocaine and alcohol, inhibit the growth of new cells in the hippocampus, which scientists believe could emotionally destabilize addicts. Understanding how drugs affect the hippocampus may have a critical role in treating addiction.
For several years now, researchers have been interested in how drugs affect a part of the brain known as the hippocampus. This region is unusual in that it can grow new neurons throughout a person’s lifetime. Researchers have theorized that these new cells help to improve memory while combating depression and mood disorders.