It absolutely should say differences. Changes implies causality (or, if not causality, at lease differences over time, which also wasn't shown). It is every bit

It absolutely should say differences. Changes implies causality (or, if not causality, at lease differences over time, which also wasn't shown). It is every bit as likely that the brain differences are the reason somebody chose to smoke marijuana. But "Study finds brain differences in young marijuana users" doesn't have any cachet.