Left lateralizing transcranial direct current stimulation improves reading efficiency.

BACKGROUND Poor reading efficiency is the most persistent problem for adults with developmental dyslexia. Previous research has demonstrated a relationship between left posterior temporal cortex (pTC) function and reading ability, regardless of dyslexia status. OBJECTIVE/HYPOTHESIS In this study, we tested whether enhancing left lateralization of pTC using transcranial direct current stimulation (tDCS) improves reading efficiency in adults without dyslexia. METHOD Twenty-five right-handed adults with no history of learning disorder participated. Real and sham "Left lateralizing" tDCS were applied to the pTC in separate sessions. Standardized word and nonword reading tests were given immediately after stimulation. RESULTS Modeling of the induced electrical field confirmed that tDCS was likely to increase left pTC excitability and reduce right pTC excitability as intended. Relative to sham, real tDCS induced improvements in word reading efficiency in below average readers. CONCLUSIONS Enhancing left lateralization of the pTC using tDCS improves word reading efficiency in below-average readers. This demonstrates that left lateralization of the pTC plays a role in reading ability, and provides stimulation parameters that could be used for a trial of tDCS in adults with developmental dyslexia. Such short-term gains could amplify the effect of appropriate reading interventions when performed in conjunction with them.