It’s a familiar feeling to many. Try to calculate a tip, and your brain seems to freeze. Attempt to figure out a relative’s age from the year they were born, and your neurons seem to dart around nervously and elude you. Just thinking about a math test makes you feel nauseous. If you’ve experienced any of these episodes, then you may have math anxiety.

It’s a bizarre phenomenon in which any problem having anything to do with numbers induces negative feelings, and even activates the part of the brain that is associated with feeling pain. It’s thought that the negative feelings take up too many of the brain’s resources, leaving little left over for actually tackling the problem. Performance goes down, and that only validates the feeling of inadequacy. It’s a vicious cycle.

In a recent article published in the Journal of Neuroscience, researchers used transcranial electric stimulation (tES) on individuals with high math anxiety while they took a simple math test. They had to answer “true” or “false” to a series of arithmetic equations, such as 6 + 2 = 16. The researchers measured reaction times for their answers. Another group of individual with little or no math anxiety was intended as a control.

Each study participant had to take the test twice: once with brain stimulation, and once without. The stimulation was applied to the dorsolateral prefrontal cortex (dlPFC). The dlPFC is an area that is implicated in so-called executive control- a function that enables an individual to regulate emotions generated elsewhere in the brain. Before and after each test, the participants gave a saliva sample, from which cortisol, a hormone that indicates stress levels, was measured.

The researchers were unsurprised to find that people with math anxiety did better at the test when they were receiving stimulation to the dlPFC than when they were not. This fits with the idea that the PFC is regulating emotions, and by enhancing positive emotion while diminishing negative emotions, individuals were able to overcome their anxiety and increase their reaction times. Additionally, they showed a decrease in cortisol levels, indicating less stress, after taking the exam while having their brain stimulated compared to when they took the test without.

The surprise came later, when the researchers realized that the brain stimulation had actually had the opposite effect on people with little or no math anxiety. They did worse on the exam when receiving the same brain stimulation, rather than better. They had higher cortisol levels, indicating more stress. Rather than being a simple control group, it turned out that the same type of stimulation exerted completely different effects on the two groups – speeding up those who were slow, but slowing down those who were fast.

It’s tempting to speculate about how this effect works. Perhaps for those with no math anxiety, the prefrontal cortex is acting as a helpful cheerleader. When that cheerleader is taken away, performance drops. For those with math anxiety, the prefrontal cortex is acting like an naysaying bully. When that bully is eliminated, performance goes up. It’s a lovely story, but it’s just that.

This is the first report we have that the effects of transcranial electric stimulation are not one-size-fits-all, but rather, depends on the traits of the person being stimulated. It’s a huge finding, indicating that scientist need to think in more nuanced ways about the experimental design.

Reference: Cognitive Enhancement or Cognitive Cost: Trait-Specific Outcomes of Brain Stimulation in the Case of Mathematics Anxiety. Amar Sarkar, Ann Dowker, and Roi Cohen Kadosh. (2014). Journal of Neuroscience 34(50): 16605-16610.