Enlarge Image Cannabinoid Research/YouTube screenshot by Chris Matyszczyk/CNET

Besides known facts like pot makes Hot Pockets look edible, we're still learning how marijuana impacts our bodies. More scientific studies are emerging on the matter, however, including one that appeared in the journal JAMA Psychiatry this week suggesting that casual cannabis use may not have as profound an effect on some parts of the brain as prior neuroimaging studies have concluded.

The study, published Wednesday, looked at data from 483 people who were also siblings, including pairs of twins between the ages of 22 and 35. Researchers broke the subjects up into three groups: pairs of siblings who had tried marijuana, pairs who had never tried it and pairs where one had tried it. Participants' data came from the Human Connectome Project, a project funded by the National Institutes of Health that collects data on the human brain for use in scientific research.

The data showed that those who had been exposed to marijuana did show shrinkage in certain parts of the brain, such as the left amygdala, which serves as the "integrative center for emotions, emotional behavior and motivation," in the words of the University of Texas Health Science Center's Neuroscience Online website.

However, researchers theorized that the reduced volume of the amygdala had more to do with certain "shared genetic factors." The study also noted that pairs of siblings where only one had been exposed to marijuana also "showed reduced amygdala volumes relative to members of concordant unexposed pairs" and concluded that these volume differences were more attributable to "common predispositional factors, genetic or environmental in origin with little support for casual influences."

Deanna Barch, the chair of Washington University's Department of Psychology in St. Louis who co-authored the study, told CNET's Crave blog that the study doesn't give marijuana users a green light (no pun intended) to get high and not worry about the effects it may have on their brain.

She noted that this study only looked at a "very limited subset among recreational users" and further study is needed to determine how other parts of the brain are affected by marijuana and if chronic use plays any role in altering the brain.

"We only looked at a limited number of things, but I think our data pointed out the need to look at how cannabis might change the brain," Barch said. "So I think our data is saying we have to take into account that it's possible that using cannabis can change the brain's use or structure, but another possibility our study points to is that there are preexisting factors in the brain's structure or behavior that makes it more likely for them to use cannabis."

The study shows that more research is needed to understand marijuana's effects on human health, Barch said.

"It points to a need for us to do good, sound scientific research on this because it's getting legalized and people are using it," Barch said. "Regardless of sociopolitical beliefs about it, the only way to understand it is do a lot of research about it."

(Via Time)