But Dr Apkarian said other research in rats had shown that spinal cord neurons die, which suggests the brain changes could be irreversible.

BBC: NEWS | Health | Pain link to permanent brain loss

Research has identified at least six possible growth-inhibiting proteins in the spinal cord, and no one knows how many need to be turned off or which ones are most important.

FORBES: Health

"Overall I'm very optimistic and I think this is a good first step in the direction of allowing some research to move forward, " said Dr. John McDonald, director of the Spinal Cord Injury Unit at Washington University School of Medicine in St.

CNN: Reaction mixed to stem cell decision

Scientists hope human embryonic stem cell research will lead to treatments and cures for many diseases, including diabetes, Alzheimer's and spinal cord injuries.

CNN: NIH announces owners of stem cells