Scientists have been trying to harness the power of electricity to enhance the functioning of the human body for centuries. Perhaps the most notable achievement, in this regard, is the invention of defibrillators that use an electric current to essentially reset a person’s heart when it is uncontrollably quivering in cardiac arrest. When not experiencing cardiac arrest, though, most people try to avoid contact with any type of an electric current that could flow through their body. But 50 years from now, there might be a significant caveat to this maxim. Many researchers around the world today are investigating whether a weak electrical current could actually have beneficial effects on our brains.
One type of electrical stimulation that is being heavily researched and has even been used by some professional athletes is transcranial Direct Current Stimulation (tDCS). Small, portable devices, powered by regular 9V batteries, are used to administer electrical current across the scalp. Some of this current theoretically reaches the brain and modulates neuronal activity. TDCS is being investigated with many promising results for use in treating a variety of neurological disorders and disabilities including Parkinson’s, Aphasia, Schizophrenia, Autism, and Learning Disabilities.
How does it actually work? TDCS transmits a very weak electrical current, typically 1-2 mA, via two or more electrodes that are placed on the scalp. This level of current has been well-tolerated in thousands of studies with the most common side effects being mild to moderate tingling and itching underneath the electrodes. One electrode (the anode) transmits a positive current through and across the scalp to the other electrode (the cathode). Both electrodes are necessary to complete the electrical circuit. While researchers have not yet identified the exact mechanisms through which tDCS works, the current that enters the brain from the anode is thought to increase the excitability of the neurons in that region, making it easier for the neurons to fire action potentials. As the current moves closer to the negative cathode, it is thought to inhibit the neurons and thus, make it less likely for those neurons to fire.
In one of the first studies of the effects of tDCS on reading skills, researchers at the University of Pennsylvania found that tDCS improved reading efficiency (a combination of speed and accuracy) in below average readers. Scientists have to carefully select the appropriate placement of the electrodes to ensure they are influencing the brain regions that support the targeted skill. In the study at UPenn, the anode was placed on the scalp over the left posterior temporal cortex since this region has been identified as a critical part of the reading network and is typically under-activated in individuals with low reading skills. The cathode was placed over the right posterior temporal cortex since the right hemisphere is typically over-activated in individuals with low reading skills. This set-up of the electrodes would theoretically encourage brain activity in the left posterior temporal cortex (underneath the anode) while inhibiting activity in the right posterior temporal cortex (underneath the cathode).
The UPenn researchers suggest that tDCS could be used as a supplemental intervention for individuals with Dyslexia to potentially increase the effectiveness of traditional interventions. Although education researchers have shown that various behavioral interventions are beneficial to students with learning disabilities, these students are still significantly more likely to fail a class in school and to experience financial hardship in adulthood. According to data reported in 2014 by the National Center for Learning Disabilities, only 68% of students with learning disabilities graduated from high school with a traditional diploma in the United States.
Preliminary studies like this one by the researchers at UPenn provide the foundation from which supplemental reading interventions, such as tDCS, could be built if additional studies prove that tDCS reliably increases reading skills in individuals with dyslexia.
Brunoni, A. R., Amadera, J., Berbel, B., Volz, M. S., Rizzerio, B. G., & Fregni, F. (2011). A systematic review on reporting and assessment of adverse effects associated with transcranial direct current stimulation. Int J Psychophysiol, 14(8), 1133–45. https://doi.org/10.1017/S1461145710001690
Cortiella, C., & Horowitz, S. H. (2014). The state of learning disabilities: Facts, trends and emerging Issues. National Center for Learning Disabilities, 1–52. https://doi.org/ncld.org/wp-content/uploads/2014/11/2014-State-of-LD.pdf
Turkeltaub, P. E., Benson, J., Hamilton, R. H., Datta, A., Bikson, M., & Coslett, H. B. (2012). Left lateralizing transcranial direct current stimulation improves reading efficiency. Brain Stimulation, 5(3), 201–207. https://doi.org/10.1016/j.brs.2011.04.002