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While transcranial direct-current stimulation (tDCS for short) has become more widely accepted as a form of treatment for various neurological and psychiatric conditions, its effectiveness in improving brain functioning such as memory and attention is a bit more controversial. Still, a recent study suggests that it can be a practical way to make human operators stay vigilant in monotonous tasks such as drone operation and cyber defense.
Using scalp electrodes to stimulate key areas of the brain has been carried out by researchers for more than a century though it still hasn't been formally approved for clinical use by agencies such as the Food and Drug Administration. When safety protocols are carefully followed, tDCS can usually be maintained for relatively brief periods with no negative effects (aside from occasional problems with skin irritation and nausea). Studies have shown good results in treating depression and more mixed results for treating other conditions such as dementia, Parkinson's disease, and schizophrenia. Tests on healthy subjects suggest that low-current stimulation to the brain can boost attention span, problem-solving, and memory though, again, these results tend to be controversial.
But what about something like vigilance? While there are numerous tasks that we can do for relatively brief periods of time, performance often suffers if we are expected to do the same task for hours at a time without breaks. Whether it involves operating heavy machinery or driving a car across the country, our minds have a tendency to wander after a while, so that the potential for making a mistake rises sharply with time. Considering that some mistakes can be literally fatal, especially for military personnel, helping workers stay focused is essential.
Traditional remedies such as caffeine or gum chewing can help to some extent but the benefits rarely last long and mistakes still occur over time. With this in mind, military researches have started taking a closer looking at brain stimulation using either direct current or transcranial magnetic stimulation (using magnets to induce electric currents in the brain). Previous studies have shown that applying tDCS to the prefrontal cortex appears to boost cognitive performance and allows soldiers to stay vigilant for longer periods during boring tasks. Since this involves very weak electrical currents (usually one to two milliamps), actual risk is minimal and changing the polarity of the current allows researchers to increase or decrease brain activity as needed.
In a recent study published in the journal Military Psychology, a team of researchers led by Andy McKinley of the U.S. Air Force Research Laboratory at Wright-Patterson Air Force Base in Ohio examined the effects of tDCS on visual search performance. The study was conducted on 11 active duty military participants (six male and five females) performing a specialized task involving pressing a keyboard whenever a red circle popped up on a computer screen. They were then presented a series of blue circles or red squares for seven seconds each with a 1.5 second break between images.
The study itself took place over four days and began with a 10-minute training session during which participants received verbal feedback to guide their performance. Then came the 30-minute main session. During the study session, each participant had specially designed electrodes attached to their scalp in different ways to provide one of three different experimental conditions (either anodal stimulation to increase neuron activity, cathodal stimulation to decrease activity, or "sham" stimulation to act as a control). In all cases, the electrodes were placed over the left frontal eye field and the order of three different conditions was randomized for each participant. Eye tracking, eye closure, and blinking were also measured as additional tests of vigilance.
During each experimental session, participants received a 2 milliamp electric current during the course of the 30-minute vigilance task. All participants went through the three experimental conditions in different sequences. There was no stimulation on the first day as it was meant exclusively for training.
According to the study results, both anodal and cathodal stimulation can provide a modest improvement in overall accuracy but this benefit seems to be very short-lived. On the other hand, accuracy during the sham condition with no current dropped significantly over time. Results for the different measures of eye movement were mixed. Blinking was also greater in the positive stimulation condition suggesting that it can be a useful measure of vigilance though changes in eye gaze and eye closure were less clear.
So, what do these result mean? While Andy McKinley and his fellow researchers only used a 30-minute task to measure the effect of direct current stimulation on attention span, what they found matches their own previous research with longer tasks. One previous study even suggested that 30 minutes of tDCS can improve cognitive performance for as much as six hours afterward though more research is still needed.
While using electric current to stimulate the brain is still controversial, largely due to the history of misuse of electroshock therapy in psychiatric patients, the potential value of less invasive methods such as tDCS can't be underestimated. With proper safety guidelines, non-invasive brain stimulation may well be used in a wide range of different applications and could help eliminate the accidents that can result from lack of attention. This includes military applications such as helping drone operators and fighter pilots stay alert longer among other things.
As Andy McKinley pointed out in a recent interview, the next step is to develop practical applications for tDCS and take it out of the laboratory. "The goal is to examine this technology and find out what it does really well and what it doesn't do well, and then tailor some solutions for particular career fields and ultimately have a device that can be used by real operators," he said.
