Doctors in the U.S. have discovered that the brain of a man so severely damaged in a car accident that he was left in a barely conscious state, has healed itself and he is now conscious and communicating with those around him.

The groundbreaking recovery has encouraged speculation that the brain is capable of repairing itself.

Terry Wallis was involved in a car accident in 1984 which left him in what doctors call a "minimally conscious state"- somewhere between being awake and being in a vegetative state.

Dr. Nicholas Schiff of Weill Medical College of Cornell University and his team believe a very slow process took place in which Wallis' brain grew new connections to heal its injured parts.

Twenty years ago Wallis suffered severe brain injuries, but was able to survive though unable to move or speak; he was able to respond with head-nodding and eye contact.

Two years ago Wallis emerged from the 19-year stupor and has regained speech and movement and it appears that his brain spontaneously rewired itself, growing tiny new nerve connections to replace the ones sheared apart in a car crash and one day he just "woke up."

Dr. Nicholas Schiff at Weill Cornell Medical College says over a three-day period, Wallis went from saying his first couple of words to recovery of fluent speech and they say his case is truly remarkable.

Dr. Schiff and colleagues found the case so intriguing that they carried out a study to examine exactly how Wallis had recovered.

By using cutting-edge imaging technology which uses color coding to show areas of growth and activity, they studied Wallis' brain over an 18 month period and found that new growth of fibers had taken place which seemed to restore function and speech, personality and even a limited ability to move returned.

Experts say the discovery is astonishing and unexpected.

It is apparently very difficult to measure consciousness and even a patient who doesn't speak, respond to voices, or move their head when spoken to might still have some level of awareness.

The public however need to be aware that there are important distinctions between being in a coma and being in minimally conscious or vegetative states.

While the term "coma" is loosely used to describe any unresponsive state, in clinical terms it occurs early in brain injury.

It is the stage in which a person is unresponsive and the eyes remain closed; once the eyes are open, it is no longer a coma.

That is when doctors must determine whether the patient has passed into a minimally conscious state or a vegetative state.

Schiff says in a vegetative state, patients show no evidence of any response to their environment, and may only have some reflex changes when they're pressed with very intense stimuli and have periods when the eyes open and the eyes close.

Schiff and his colleagues admit they are unsure what caused Wallis to wake up in the first place, but pictures of his brain captured since then offer unequivocal proof that his brain is somehow mending itself.

Although the ultimate goal is to eventually be able to predict which patients have the best chance of recovering consciousness, experts warn that this research is very preliminary and stress that the brain is the most complicated organ, and trauma is the most complicated injury.

The study is published in the Journal of Clinical Investigation.