You know, doctors don't know everything. The MRI will only show dead areas.
Scars. It does not show, impairments in the chemistry of the brain cells.

You really don't know what was mixed in that drug overdose.There could have been contaminants, and other drugs used to "cut" it.

It you damage neurons, but they remain alive, just non-functioning, I don't think that would show up on tests. Perhaps a PET scan might reveal something.

We are just discussing hyperbaric oxygen on the PN forum.
I'll give you this link:
http://www.aurorahealthcare.org/serv...rbaric/faq.asp
and
http://www.emedicine.com/plastic/topic526.htm

I saw a show about a child who was in a car crash, and had a closed head injury. He was able to regain many faculties after these treatments. It was on a science show several years ago. Hyperbaric treatments should be monitored by a doctor, if you decide to try it.

There is a form of Parkinson's that is acquired from bad heroin:
http://everything2.com/?node_id=1107315
I hope this is not the case for you.

The brain is very complex and still puzzling for many doctors. So an answer for you may not be forthcoming until more is learned.

I hope with time you may heal. Sometimes things take a while.