NEW YORK (AP) - A small study of casual marijuana smokers has turned up evidence of changes in the brain. Researchers say they need to study whether the brain changes will cause trouble later on.

The 20 young adults who volunteered for the study were not dependent on pot, nor did they show any problems related to marijuana use. The scientists scanned their brains and compared the results to what scans showed in 20 non-users.

The pot smokers showed differences in density and shape of two brain regions, compared to the non-users. Those regions are associated with emotion and motivation. The more marijuana the users said they'd been using, the more pronounced the differences were.

Results appear in Wednesday's issue of the journal of neuroscience.

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