I am not a doctor - but I think "biologically" means its in his make up. I think, rather than learned, or by environment factors. Like the biology of the brain (neurotransmitters and the natural occuring chemistry of the brain). Many things do affect our brain chemistry - through our entire lives. Biologically is different than learned behaviors. I do not think of brain damage when I think of biologically based - more like - it works differently, and is not a learned difficulty. Like I said - I am definitely no doctor though. I hope this helps - but I would be more inclined to look at the definitions and such (google!) Best of luck to you and your son!