The strategy behind transcranial direct current stimulation (tDCS) devices seems hare-brained enough to be science fiction: Stick some electrodes on a human scalp, run low levels of electricity through it, and hope the current reignites dull or absent brain functions by getting neurons excited. The crazy part is that sometimes, it actually works. In a recent study, scientists found that it has the potentially to jumpstart what’s arguably the most important function of the brain — consciousness.
They made this discovery by sticking the electrodes on people who, as a result of traumatic brain injury, were in a “minimally conscious state” — that is, they were awake and their awareness flickered (people who are in the more severe “vegetative” state are awake but show no signs of awareness). As the scientists, from Belgium’s University of Liège, described in the journal Brain Injury in March, nine of the 16 participants that got daily tDCS treatments showed increased awareness after five days. A couple of them even began to communicate.
The study was a follow-up to an experiment the researchers had published in Neurology in 2014, in which a single session of tDCS produced “reproducible but inconsistent signs of consciousness” in people with minimal consciousness. These vague but positive results led them to ask: What would happen if they received more tDCS?
A lot, apparently.
At the start of the new experiment, all of the participants had been in a minimally conscious state for at least three months, which the scientists took as a sign that they probably weren’t going to recover. Each person got 20 minutes of tDCS for five straight days (control patients got a sham treatment), in which electrodes were positioned on top of the left prefrontal cortex, the part of the brain that’s associated with consciousness. After the first five days of treatment, nine of them started to behave differently: They seemed like they had woken up.
The “responders” clearly showed what the researchers called “new signs of consciousness”. These included the ability to respond to a command (“Move your hands!”), visual pursuit (“Follow this with your eyes!”), and the ability to recognize objects and react to noxious stimuli. Two of them were even able to intentionally communicate, using their bodies, in response to questions. After the five-day treatment, the effects lasted for at least a week before the responders drifted back into their minimally conscious states. Meanwhile, the control participants, who hadn’t received any tDCS, didn’t show any signs of improvement at all.
These findings, though extremely premature — the researchers only assessed patients for a week after treatment, and they have no idea whether tDCS has any negative long-term effects — gives credence to the possibility that people in comas could, someday, be brought to the conscious realm more fully. Even more promising is the fact that tDCS is relatively cheap and easy, as far as brain stimulation goes, so there’s potential for patients to get zapped in at-home treatments.
But tDCS is still in its early stages. Moving electrical currents are ultimately what make up the difference between a dead brain and a living one — but to what extent, and in what patterns, those currents are supposed to move isn’t exactly clear. Scientists have yet to determine what consciousness looks like in an electrical map of the brain (though new research into psychedelics has given them some insight), let alone how to induce that sort of electrical activity artificially — and with a tool as imprecise as tDCS. Still, the results of this experiment speak for themselves: Something about this technique works.