People in a vegetative state showed signs of awareness after electric brain stimulation – and minimally conscious people were able to communicate again
TALK about an awakening. People who have been in a minimally conscious state for weeks or years have been temporarily roused using mild electrical stimulation.
Soon after it was applied to their brains, 15 people with severe brain damage showed signs of consciousness, including moving their hands or following instructions using their eyes. Two people were even able to answer questions for 2 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 "awaken", by showing 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 might show fluctuating signs of awareness, which come and go, 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. So Laureys and his colleagues wondered if it would do the same in 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, says Laureys. "Two patients emerged from a minimally conscious state altogether." When asked questions such 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 2 hours. The findings will be published in the journal Neurology.
For some patients, it was only weeks since their trauma had happened, but others had been minimally conscious for years. This is important, says Laureys. "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 a standard practice, he says, it will reveal a lot about how different brain networks become reactivated after severe head trauma.
It's not clear exactly how the treatment works, but it is likely 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, Pennsylvania, says that tDCS might be used both as a treatment in its own right, and for screening people to diagnose their state and assess what treatment they might 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 now doing just that – assessing the potential for more lasting arousal. The brain can be stimulated for longer periods of time as 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. The results are not yet available.
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 patients with brain damage (Functional Neurology, in press).
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