A Northwestern University study found that chronic back pain shrinks the brain by about 11%, which is equivalent to the amount of gray matter lost in 10 to 20 years of normal aging. The overall loss found in the brain density had to do with the duration of chronic pain. Approximately 1.3 cubic centimeters of gray matter (the part of the brain that processes information and memory) are lost for every year of chronic pain. People with chronic pain for 6 months or longer, had also shown abnormal brain chemistry in the areas of the brain important for emotions, decision-making, and social behavior. The study stated that it was possible that the loss of gray matter seen was primarily tissue shrinkage without neuron loss and proper treatment could reverse the brain shrinkage. Chiropractic has been shown to be effective for long term relief of back pain.
http://www.northwestern.edu/newscenter/stories/2004/11/chronic.html