Did you know chiropractors used to run mental institutions, sanitaria, and hospitals etc? I speak on mental health and chiropractic in my seminars. I'm always on the lookout for information related to this subject - look at these two articles I found:

Head Injury and Depression

It's well accepted that after a head injury a person can have depression and cognitive problem, sometimes for months. But what about long term problems? Some researchers investigated just that. They reviewed people people's medical records 50 years after a head injury.
They reviewed the medical records of soldiers who were hospitalized for head injury, pneumonia, laceration, puncture or incision wounds. (Men with dementia were excluded from the study.) The researchers found that the risk of depression remained elevated for decades following head injury. The risk was highest in those who had a severe head injury. (Head injury in early adulthood and the lifetime risk of depression by Tracey Holsinger et al. from the Archives of General Psychiatry. (2002); 59:17-22.)

Head Injury and Alzheimer's Disease - 50 year follow-up to head injury!

Researchers from the US National Institute on Aging and Duke University have reported a strong correlation between head injuries as a young adult and the development of Alzheimer's disease 50 years later(!)
The authors of the study "have no idea how the injury leads to the neurological deficit later in life," (what do you expect?) but draw a direct correlation to the severity of the injury and likelihood that the patient eventually will be diagnosed with the illness.
Those that had experienced a loss of consciousness or amnesia for less than 24 hours after the injury were twice as likely as the general population to suffer from Alzheimer's disease. For those that lasted 24 or more hours, the risk quadrupled. The study involved over 1,700 veterans; the time between the injury and the development of Alzheimer's disease was about 50 years. (Neurology, Oct 24, 2000.)

While we're on the subject did you know that people who suffer whiplash have more health problems? Of course you did!  Here's a quote:The association between exposure to a rear-end collision and future health complaints Anita Berglund a, *, Lars Alfredsson b , Irene Jensen a , J. David Cassidy a,c , Ake Nygren a (Journal of Clinical Epidemiology 54(2001)851-856)
Swedish researchers investigated 232 people in rear-end collisions who had whiplash and 204 in rear-end collisions who didn't report whiplash 7 years later. The whiplash people had more "headache, thoracic and low back pain…fatigue, sleep disturbances and ill health." What did they mean by ill health? Dis-ease? Their conclusion is great: "There is a need to identify factors that predict a non-favorable outcome in order to improve clinical management."  Its called SUB-LUX-ATION gang.

I think I'll keep driving!