Neuromodulation by transcranial direct current stimulation: investigation on reading processes

Reading is a human skill, fundamental for everyday life, in which a lot of information is given in written form. To explain this process, several theories were advanced: currently there is common agreement on the simultaneous activation of two ways of reading, the direct or lessical one for words, and the phonological one for non-words or novel words. Neuroimaging studies converge in identifying three basic systems for reading, mostly in the left hemisphere: among these, the temporoparietal cortex (TPc) seems to be involved in grapheme to phoneme conversion (phonological route). The aim of the present work is to investigate, through transcranial direct current stimulation (tDCS), the role of TPc in words and non words reading. We also want to investigate different parameters of stimulation. Results of first study suggest bilateral TPc role in reading, and a facilitatory effect of left cathodal-right anodal stimulation on reading onset times. The second study suggest that reference electrode can lead to different effects depending on its position, and that unilateral montage is not as effective as bilateral one, not involving both TPc. The third study suggest that 10 minutes of tDCS are not enough to achieve a modulation, but confirm the role of TPc. The last study with below average readers, suggest that activation state of the stimulated area and difficulty of the task have to be considered too. This work contributes to the study of neural bases of reading and on the functioning of transcranial direct current stimulation on cognitive functions