I have no problem with the study [1]. However, I encourage you to search the study for any reference to 'brain damage.' I also encourge you to consider whether the mean frequency of cannabis use, 11.2 joints per week, really qualifies as 'casual' use.
Are you implying that the study does not report findings of brain damage? Then you are wrong. Scientific texts tends to be as specific as possible which is why they write "deformations in brain part X, Y, Z" instead of the more general term "brain damage."
You know what else causes 'brain damage,' according to this logic? Becoming a London cab driver[1] or a musician [2]. You know what actually causes brain lesions? Alcohol.[3]
[1] http://jn.sfn.org/press/April-16-2014-Issue/zns01614005529.p...