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While brain scans can contribute a great deal to our understanding of mental illness, addiction and how the brain works ordinarily, their effects on journalists are not so positive. Take the lead of this story by the AP, covering a study of marijuana:

“New findings on marijuana's damaging effect on the brain show the drug triggers temporary psychotic symptoms in some people, including hallucinations and paranoid delusions, doctors say.”

As anyone who has ever smoked marijuana or watched a Cheech and Chong movie could tell you: “Duh!”  The fact that marijuana produces paranoia and hallucinations temporarily is not exactly headline-making. And calling this a “damaging effect on the brain” is misleading: damage implies permanent, detrimental changes; the brain scans in question show only a moment in time when the subjects were high, not what happened afterwards. By the same token, eating chocolate, having sex, or going for a run could all be classified as having a “damaging” effect on the brain.

Which is why it’s important to note when covering brain scan-based research that a “change” in the brain isn’t necessarily a bad thing: learning, falling in love, seeing, hearing and virtually any other experience can be expected to cause changes in the brain.  If something doesn’t cause a change, it hasn’t been remembered or experienced.  The tricky part is determining what brain changes mean.

The study in question did find interesting things about the areas of the brain affected by marijuana. But the AP claimed that it “provides physical evidence of the drug's damaging influence on the human brain,” which is simply not a conclusion that can be drawn from this data. Scanning someone’s brain while they are under the influence of a drug tells us nothing about what that brain is like when they are not under the influence.

This study looked at users while they were high, so it cannot offer any information about after-effects. Only a study that scanned the same people repeatedly over a long period of time could do that. Journalists need to understand what brain scans can and cannot prove, especially as such data moves from the lab into the courtroom and legal system.

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