CHICAGO (CBS) — A new study presented at a medical conference in Chicago today raises questions about how safe it is for teenagers to play high school football, reports WBBM’s Regine Schlesinger.

The study by Dr. Christopher Whitlow of Wake Forest School of Medicine measured the brain activity of high school players even when they didn’t suffer concussions. It found brain changes that were more pronounced the harder they took hits to their heads.

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Whitlow says its concerning, but there are still many questions about the meaning of those changes.

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“Do these changes persist or do they go away?” said Dr. Whitlow. “Are they associated with any subtle cognitive or behavioral changes that maybe aren’t really apparent? What happens after multiple seasons of exposure and all of these questions are ones that we have no answer to at this time.”

He is not telling parents to keep their kids from playing football but rather to get involved in the program and work to minimize the head hits they take.

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Dr. Whitlow presented the study to the Annual Radiological Society meeting Monday at McCormick Place.