Washington - People who have been in a minimally conscious state for weeks or years have been temporarily roused using mild electrical stimulation.
Soon after the stimulation was applied to their brains, 15 people with severe brain damage showed signs of consciousness, including moving their hands and following instructions using their eyes. Two were able to answer questions for two hours before drifting back into their previous uncommunicative state.
“I don’t want to give people false hope – these people weren’t getting up and walking around – but it shows there is potential for the brain to recover functionality, even several years after damage,” says Steven Laureys at the University of Liège in Belgium, who led the research.
People with severe brain trauma often fall into a coma. If they show signs of arousal but not awareness, they are said to be in a vegetative state. This can improve to a state of minimal consciousness, where they may show intermittent signs of awareness, but have no ability to communicate.
External stimulation of the brain has been shown to increase arousal, awareness and aspects of cognition in healthy people. Laureys and his colleagues wondered if it would do the same for people with severe brain damage.
They used transcranial direct current stimulation (tDCS), which doesn’t directly excite the brain but uses low-level electrical stimulation to make neurons more or less likely to fire.
The team worked with 55 people who had experienced a traumatic brain injury or lack of oxygen to the brain and were in a minimally conscious or vegetative state. They placed electrodes over their left dorsolateral prefrontal cortex, an area involved in memory, decision-making and awareness. Then they delivered 20 minutes of stimulation to some of the people and a sham treatment to the others. The next day, the two groups received the opposite therapy.
During brain stimulation, 13 people with minimal consciousness and two people in a vegetative state showed signs of awareness that were observed neither before the stimulation nor after the sham treatment. For most of these people, the changes were moderate, but some recovered the ability to communicate, Laureys says.
“Two patients emerged from a minimally conscious state altogether.”
When asked such questions as “Am I touching my nose?” they were able to answer by nodding their head or making specific eye movements.
Others were able to respond to simple commands to nod or squeeze their hand. All the effects lasted for about two hours. The findings will be published in the journal Neurology.
For some patients, it was only weeks since their trauma happened, but others had been minimally conscious for years. This is important, Laureys says. “There’s this dogma that if you don’t see a change in 12 months, you will never see it. This research challenges that.”
“This is a very important study,” says Tristan Bekinschtein, who studies consciousness at the University of Cambridge.
If this treatment becomes standard practice, he says, it will reveal a lot about how different brain networks become reactivated after severe head trauma. It’s not clear how the treatment works, but it is possible that the stimulation pushes previously suppressed brain activity over a threshold. This possibly enhances processes that are involved in attention and working memory and underlie conscious tasks such as decision-making and moving.
John Whyte, director of the Moss Rehabilitation Research Institute in Philadelphia, says that tDCS may be used as a treatment in its own right and for screening people to diagnose their state and assess what treatment they may respond to.
“This research is of considerable interest, as it suggests another potential treatment avenue,” he says. “First, we need to determine whether these short-term effects can be amplified and made more durable.”
Laureys’s team is doing just that: assessing the potential for more-lasting arousal. The brain can be stimulated for longer periods, because there seem to be no side effects, just a little tingling, Laureys says. Trials involving a full week of stimulation are under way. They also involve stimulating other areas of the brain.
This isn’t the first time that medical interventions have aroused a silent brain. In 1999, Louis Viljoen, who had been in a persistent vegetative state for three years, began to make erratic movements at night. His doctors prescribed zolpidem, a sedative used to treat insomnia.
Within minutes of being given the drug by his mother, Viljoen turned his head and said, “Hello, Mummy”. The effect lasted a few hours. The drug now allows him to communicate for about 10 hours a day.
Such a response is rare. Laureys’s team found that zolpidem had no significant effect on any of 60 other patients with brain damage.
It isn’t known how a sedative can rouse some patients. It may be that the damaged brain reacts differently from the way other brains do. A drug used to treat Parkinson’s disease called amantadine has also been found to help minimally conscious patients recover, possibly by increasing dopamine levels in brain networks vital to awareness and attention.
When people temporarily emerge from a minimally conscious state, it’s hard to gauge how much they are aware of. Laureys suggests it may be like that moment when you wake up in a hotel and don’t know where you are. But these trials raise uncomfortable questions, such as: is it right to rouse someone, only to send them back to sleep a few hours later?
Such concerns can be challenging, Laureys agrees. The patient’s family are often in the room during a trial. “We explain to them that the effect will be of limited duration and that there is no room for subjectivity, so we can’t just ask any question. We need to keep all the trials the same.”
In Laureys’s experience, the families are just happy that new therapies are being tested.
“It’s like we’re opening and shutting a window for a few hours, and that could be perceived as cruel,” says Joseph Fins, at the Weill Cornell Medical College in New York, who was the first person to test deep-brain stimulation in a minimally conscious person.
“But we didn’t give these people brain damage – we are trying to make it better. These kinds of experiments show that a window exists, and you may be able to use other interventions to enhance that window.”
Brain stimulation might some day be added to the tests used to diagnose persistently vegetative state. It’s an important issue: someone in a vegetative state is thought to be unable to feel pain, whereas someone with minimal consciousness can feel pain and possibly emotions, too.
“The key thing is getting the diagnosis right; that’s the game-changer,” Fins says.
It could also give doctors another tool to decide whether there is any chance of recovery for millions of people living with disabilities caused by traumatic brain injury.
“In some cases, members of your family can be left with difficult decisions about whether to remove life support,” Laureys says.
“We can’t make any decisions ethically if we’re not sure about the diagnosis, prognosis and therapeutic options.”
Laureys says that while you are healthy, you should discuss with friends and health professionals what you think is an acceptable quality of life and where you draw the line. – New Scientist/The Washington Post News Service