Neural plasticity

New Scientist reports:

A study of the "miraculous" recovery of a man who spent 19 years in a minimally conscious state has revealed the likely cause of his regained consciousness.

The findings suggest the human brain shows far greater potential for recovery and regeneration then ever suspected. It may also help doctors predict their patients’ chances of improvement. But the studies also highlight gross inadequacies in the system for diagnosing and caring for patients in vegetative or minimally conscious states.

In 1984, 19-year-old Terry Wallis was thrown from his pick-up truck during an accident near his home in Massachusetts, US. He was found 24 hours later in a coma with massive brain injuries.

Within a few weeks he had stabilised in a minimally conscious state, which his doctors thought would last indefinitely. It did indeed persist for 19 years. Then, in 2003, he started to speak.

Over a three day period, Wallis regained the ability to move and communicate, and started getting to know his now 20 year old daughter – a difficult process considering he believed himself to be 19, and that Ronald Reagan was still president.

To try and find out what was going on inside Wallis's brain, Nicholas Schiff and colleagues from the Weill Medical College of Cornell University in New York City, used a new brain imaging technique called diffusion tensor imaging (DTI). The system tracks water molecules and so reveals the brain’s white matter tracts – akin to a wiring diagram. They combined this with more traditional PET scanning, to show which brain areas were active.

The team's findings suggest that Wallis’s brain had, very gradually, developed new pathways and completely novel anatomical structures to re-establish functional connections, compensating for the brain pathways lost in the accident.

They found that new axons – the branches that connect neurons together – seemed to have grown, establishing novel working brain circuits.

Surprisingly, the circuits look nothing like normal brain anatomy. A lot of the damage had been to axons that passed from one side of the brain to the other, torn by the force of the accident. But Schiff says that new connections seem to have grown across around the back of the brain, forming structures that do not exist in normal brains.

There were also significant changes between scans taken just two months after the recovery, and the most recent, at 18 months. Some of the new pathways had receded again, while others seem to have strengthened and taken over as Wallis continued to improve.

Krish Sathian, a neurologist and specialist in brain rehabilitation at Emory University School of Medicine in Atlanta, US, describes it as an amazing finding. “The bounds on the possible extent of neural plasticity just keep on shifting,” he says. “Classical teaching would not have predicted any of these changes.”

Knowing the mechanism will be important for identifying whether a particular unconscious patient could improve, says Schiff, potentially allowing doctors to target their rehabilitation efforts.

But improvements in the care of patients could be made without putting every patient into a brain scanner, says Schiff. There is currently no system for even a bedside re-examination at 8 weeks after an initial diagnosis, despite the fact that “their whole prognosis might change”, he says.

Wallis was frequently classified as being in a permanent vegetative state. Though his family fought for a re-evaluation after seeing many promising signs that he was trying to communicate, their requests were turned down.

“A careful bedside examination at 6 months [after the accident] would have unequivocally said he was not in a vegetative state,” says Schiff. There is a much greater chance of a late recovery from a minimally conscious state, he adds, although such recoveries are still rare. “The Wallis case will force the issue,” he believes.
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