November/December 2010

Electric current boosts math forte

Electrically stimulating the brain makes it easier for people to perform particular numerical tests, suggesting a similar technique may one day help people with math deficiencies, according to a study published in Current Biology. The researchers used a noninvasive technique called transcranial direct current stimulation (TDCS), in which scalp electrodes emit current that modulates the activity of populations of neurons that lie underneath them. Volunteers who received current over their right parietal lobe, a brain region at the back of the head known to contribute to spatial and math aptitude, became more proficient at tricky numerical tasks as they learned them over the course of about a week.

TDCS increases or decreases the threshold of neural excitability, depending on the direction of current flow between electrodes, causing neurons to become more or less likely to respond to the same stimuli. Current flow in one direction reduces the activity of inhibitory neurons, causing overall excitation, whereas current flow in the other direction reduces activity in excitatory neurons, causing overall inhibition.

In the study, one group of subjects received excitatory current over the right parietal lobe and inhibitory current over the left parietal lobe, and a second group experienced the opposite pattern of stimulation. Over the span of six days, the investigators applied current for 20 minutes at the beginning of training sessions in which they taught volunteers to associate numbers with arbitrary symbols, such as triangles or cylinders.

By the fourth day, subjects who received excitatory current over the right hemisphere became slower for incongruent trials compared to congruent trials, similar to adults responding to real digits. But those whose right hemispheres were inhibited showed no difference between these trials. The results suggest that right-hemisphere excitation causes subjects to learn to process the symbols automatically and therefore perform more like adults with everyday digits, whereas inhibition keeps performance in a child-like state.

Six months after training, volunteers who previously underwent right-hemisphere excitation repeated the tasks and performed similarly. There were no control groups to prove that the precise pattern of stimulation caused the long-lasting effects.

In the future, the authors plan to investigate how the technique induces changes in the brain and try it in people with developmental dyscalculia, a learning disability that affects math skills.