Nerve regeneration after 20 years in a minimally conscious state

Brain scans performed on Terry Wallis, who in last month awoke after nearly 20 years in a minimally conscious state (MCS), reveal that his recovery is due to the regrowth of neural connections in the damaged areas of his brain. 

Wallis has been unable to move or speak since incurring severe brain damage in a motor vehicle accident 19 years ago. Because MCS was only classified as a condition several years ago, Wallis’s parents were told soon after his accident that he was in a coma. They continued communicating with Terry but had no idea whether or not could understand them.

Several years ago, Terry started responding to his parents by grunting and blinking, and last month, to everyone’s surprise, started speaking. It would appear that Terry also suffers from anterograde amnesia, or the inability to form new memories; when asked by his mother to name the president of the United States, his answer was “Ronald Reagan.”

Henning Voss and colleagues, at Cornell University’s Weill Medical College in New York, imaged Wallis’s brain and compared the results to those obtained from another patient in the same condition who had shown no signs of improvement. The scans of Wallis’s brain revealed high levels of metabolic activity in the white matter, which is composed of the processes which connect neurons to each other, in comparison to other MCS patient. But because Wallis’s brain was only scanned recently, there are no data available to determine the rate at which the white matter has regenerated.

 One of the areas in Wallis’s brain with increased metabolism was the precuneus (the posterior medial parietal lobe). In healthy people, the precuneus and surrounding areas have among the highest resting metabolic rates in the brain. Imaging suggests that the precuneus is involved in tasks such as visuo-spatial imagery and the retrieval of episodic (or ‘autobiographical’) memory. Activity in the precuneus  decreases during the performance of non-self-referential goal-directed tasks, and also during altered states of consciousness such as sleep, vegetative states and drug-induced anaesthesia. This has led some to hypothesize that precuneus activity  correlates to self-consciousness.

Although Wallis’s case does not provide any clues about how nerves can be coaxed to regenerate, it has led to the questioning of a central dogma. Neurologists have always assumed that the brain’s capacity to recover from trauma is limited to weeks or months after damage has occurred, and that the likelihood of recovery decreases with time. The case of Terry Wallis has turned these assumptions upside down.

About these ads