Imagine a medical device that is so simple to build and cheap to acquire that anyone with an Internet connection and a local Radio Shack can use it tweak their brains—to become smarter, more focused, calmer, or happier. Such a device nominally exists. Transcranial direct current stimulation (tDCS) involves sending low-current electricity into the brain via carefully placed electrodes attached to the scalp. Our best current guess is that the electricity puts neurons in a state that leads them to fire (send out signals) more readily after receiving input from other neurons. The result is a temporary change in the brain that could, in theory, be helpful to those who want to learn faster, to improve their mood, or to modify their mental functioning in any way.
A growing number of scientific studies is beginning to detail the ways in which tDCS can increase focus, improve mood and sharpen memory. For example, in a 2014 Journal of Neuroscience article, neuroscientists Robert Reinhart and Geoffrey Woodman from Vanderbilt University demonstrated that tDCS applied over medial frontal cortex caused individuals to learn a simple reaction time task more quickly and to correct themselves more readily after making an error. Further, reversing the polarity of stimulation reversed the effects, making people worse at correcting themselves than when they received sham stimulation, which mimics the sensation of electrical current without delivering electricity. These results were replicated across four experiments, and were observed in two types of tasks. In short, the authors found that changing activation in regions of the brain associated with cognitive control improved people’s cognitive control, supporting the idea that the medial frontal cortex really does govern this function, and that such control can be modified. This work is complementary to techniques such as functional magnetic resonance imaging (MRI) that allow scientists to look for associations between brain regions and cognitive processes, but cannot show that activity in those regions truly underlies memory, attention or language.