A cognitive scientist from the Sandia National Laboratories, Mike Trumbo, has demonstrated that, under certain conditions, transcranial direct current stimulation (tDCS) can improve both working memory capacity and general cognition.
According to Trumbo, the reason this type of non-invasive brain stimulation works is because of its direct impact on plasticity in brain regions relevant to the performance of working memory – an effect that carries over to other tasks reliant on that same region.
Conversely, whenever people are asked to engage in tasks in the absence of brain stimulation, improvements can be specific to the task at hand, with little to no effect on overall cognitive ability.
In the study, 70 volunteers, divided into six groups, underwent working memory training and were then asked to complete a series of tests to gauge their working memory and problem-solving ability.
Transcranial stimulation is thought to encourage neurons to fire more readily, although the exact mechanism is not yet known.
Some of the effects, however, are already apparent – research shows that tDCS can help participants to remember people’s names, is better than caffeine at keeping Air Force personnel awake and may help treat depression.
In the study, volunteers played verbal or spatial memory training games while receiving stimulation to the left or right part of the forehead – a part of the brain (called the dorsolateral prefrontal cortex) responsible for working memory and reasoning.
Given that the right hemisphere is involved in spatial tasks and the left hemisphere – in verbal tasks, the researchers thought the results would be fairly straightforward.
For the most part, that’s exactly what happened – participants got better at the trained task while having a corresponding brain region stimulated, but not at the other task (the effect was roughly the same as the groups receiving sham stimulation).
Surprisingly, though, the verbal/right group got better at the trained task – remembering strings of letters, a related task – remembering sequences of boxes in a grid, and a reasoning test. The effect was statistically significant.
One explanation Trumbo offered is that the right dorsolateral prefrontal cortex is particularly involved in strategy use during tasks. By stimulating the right side during the verbal task, the volunteers might get better at using a strategy. The tDCS improves the connections of these neurons, which leads to enhanced ability to use this strategy, even on other tasks.
In the future, this could lead to improved cognitive performance and decreased training time.