A new study based on research at Oxford University suggests that brain stimulation equipment used to strengthen cognitive behavior may not be safe and could potentially cause impairments that hinder the brain's functioning ability.

The study, published Dec. 10 in the Journal of Neuroscience, found that different forms of brain stimulation affected a group of students differently, with some benefiting from it and others not, according to The Guardian.

Brain stimulation consists of a battery device that transmits currents to electrodes that are attached to particular areas of a person’s head in order to increase stimulation in that area of the brain.

Students who underwent the brain stimulation experiment were asked to do so while solving basic math problems. Scientists first used transcranial direct current stimulation (tDCS) on each student’s dorsolateral prefrontal cortex, which plays an important role in thinking and performing actions. They applied anodal tDCS to the left side and cathodal tDCS to the right in order to reduce negative emotions such as stress and anxiety. During the experiment, scientists switched over for 30 seconds to sham stimulation in which a brief current is released and subjects think stimulation has remained the same. Sham, used mostly as a control factor in experiments, should have no real impact.

Results found that tDCS helped worried students to calm themselves and control their anxiety when completing problems but that when under sham, they and those that were not nervous were less successful when confronted with the same task. Measurements of the stress hormone cortisol showed that anxious students were better able to control their anxiety than less nervous students when they underwent brain stimulation.

“From these lab experiments we can see that some people will benefit and some will have impairment,” the study's lead scientist Cohen Kadosh told The Guardian. “With DIY tDCS we cannot know if it’s helping, or has no effect, or if it’s damaging.”

Scientists performed an additional test in which each student was asked to identify the direction of an arrow shown to them on a screen with information placed next to it as a distraction. All the students under brain stimulation did poorly on this task.

The experiment comes at a time when a high number of consumers are purchasing brain stimulation equipment online or are putting devices together themselves. This puts people at risk of shocking and injuring themselves, according to The Guardian.

“It’s not something people should be doing at home at this stage,” Kadosh told The Guardian. “I do not recommend people buy this equipment. At the moment it’s not therapy, it’s an experimental tool.”

Nick Davis, a brain stimulation expert at Swansea University says that how a person responds to brain stimulation is important in assessing its effectiveness in helping brain activity and function.

“Neuroscientists often ‘sell’ the benefits of their work without really talking about the drawbacks, but it’s an important thing to do,” he told The Guardian. “There are some real cognitive enhancements to be had with tDCS, but I also think at the moment we don’t understand it well enough to make it generally available.”