Parietotemporal Stimulation Affects Acquisition of Novel Grapheme-Phoneme Mappings in Adult Readers

• Published in: Frontiers in human neuroscience Vol. 12; p. 109
• Main Authors: Younger, Jessica W, Booth, James R
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Research Foundation 23-03-2018; Frontiers Media S.A
• Subjects: Adults; artificial orthography; Brain; Brain mapping; Brain research; Dyslexia; Electrical stimulation of the brain; ESB; Grapheme phoneme correspondence; Language; Learning; Medical imaging; Neuroimaging; Neuroscience; Orthography; Parietal lobe; parietotemporal cortex; Phonemes; Phonology; Reading; reading acquisition; reading skill; Studies; Synesthesia; Transcranial direct current stimulation; United States > US; reading skill; reading acquisition; artificial orthography; parietotemporal cortex; transcranial direct current stimulation
• ISSN: 1662-5161; 1662-5161
• DOI: 10.3389/fnhum.2018.00109

Neuroimaging work from developmental and reading intervention research has suggested a cause of reading failure may be lack of engagement of parietotemporal cortex during initial acquisition of grapheme-phoneme (letter-sound) mappings. Parietotemporal activation increases following grapheme-phoneme learning and successful reading intervention. Further, stimulation of parietotemporal cortex improves reading skill in lower ability adults. However, it is unclear whether these improvements following stimulation are due to enhanced grapheme-phoneme mapping abilities. To test this hypothesis, we used transcranial direct current stimulation (tDCS) to manipulate parietotemporal function in adult readers as they learned a novel artificial orthography with new grapheme-phoneme mappings. Participants received real or sham stimulation to the left inferior parietal lobe (L IPL) for 20 min before training. They received explicit training over the course of 3 days on 10 novel words each day. Learning of the artificial orthography was assessed at a pre-training baseline session, the end of each of the three training sessions, an immediate post-training session and a delayed post-training session about 4 weeks after training. Stimulation interacted with baseline reading skill to affect learning of trained words and transfer to untrained words. Lower skill readers showed better acquisition, whereas higher skill readers showed worse acquisition, when training was paired with real stimulation, as compared to readers who received sham stimulation. However, readers of all skill levels showed better maintenance of trained material following parietotemporal stimulation, indicating a differential effect of stimulation on initial learning and consolidation. Overall, these results indicate that parietotemporal stimulation can enhance learning of new grapheme-phoneme relationships in readers with lower reading skill. Yet, while parietotemporal function is critical to new learning, its role in continued reading improvement likely changes as readers progress in skill.