Anodal transcranial direct current stimulation over the left temporoparietal cortex facilitates assembled phonology

A major challenge in learning to read an alphabetic language is to learn to map graphemes to phonemes (i.e., assembled phonology). Previous imaging studies have revealed that the left temporoparietal cortex (LTPC) is associated with assembled phonology. By combining high-definition transcranial direct current stimulation (HD-tDCS) and an artificial language training paradigm, the present study aimed to examine the causal role of LTPC in assembled phonology and tDCS's short- and long-term facilitation effect on reading via assembled phonology. Two matched groups of native Chinese speakers received anodal tDCS either on LTPC or the visual cortex before they were trained to read an artificial language. All participants learned two sets of words, one through assembled phonology and the other through addressed phonology. We found that tDCS on LTPC specifically facilitated learning via assembled phonology, but not that via addressed phonology. Furthermore, the beneficial effect was still present four days later, indicating that repeated applications of tDCS at LTPC had long-term benefits on assembled phonology. These results have both theoretical and practical implications for learning to read.