Hi there,
I don't think this about brain damage. I do feel your son, may need med. dose change or actually a different med or combo.
If he is in puberty (teens) hormonal changes can also factor in to bahavioral changes, not a definate thing, but possible. Have you spoke to another pdoc? If the present one is not answering your question(s) and avoids doing so, I would personally seek a new one.
Lithium is an excellent med. for mania, has a long track record when compared to newer mood stabilizers for Bipolars with severe and/or violent manic episodes.
Seroquel (sp?)I know is fiarly new, I am not too familiar with, you may ask his pdoc if this is interferring with the Lithium's efficiency.
My brother has been on Lithium alone for over 30 years and has been a Godsend, before he was put on this, the few other meds availble (sp?) were not effective, actually made his episodes more violent and even caused some hallucinations.
My suggestion again, is to contact his pdoc and demand answers to questions regarding medications, dosages, and other alternatives if any.
I wish you lots of luck and inner strength with this matter.
Welcome to the forum(s), you will meet many supportive, compassionate, and informative people willing to listen and reply.


PS
Try Drug Questions forum to see if T_MD, Larry, or Cam can help you with meds. and effacy, they are professionals, and are so very helpful to us here. Visiting many of our forums can help gather more info, and share other's experiences with this, there is so much involved dealing and working through this disorder as well as other disorders.
Lots of good wishes and luck to you and your son.

Sincerely,
DE