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The role of anterior temporal lobe in reading: an HD-tDCS study
Poster Session A, Friday, September 12, 11:00 am - 12:30 pm, Field House
Sophie Arheix-Parras1, Cheng Xiao1,2, Sidney Crouse1, Nicholas Riccardi1, Karim Johari3, Rutvik H. Desai1,4; 1Department of Psychology, University of South Carolina, 2Linguistics Program, University of South Carolina, 3Human Neurophysiology and Neuromodulation Lab, Communication Sciences and Disorders, Louisiana State University, 4Institute for Mind and Brain, College of Arts and Sciences, Columbia
Introduction. The anterior temporal lobe (ATL) is involved in lexicosemantic processes and in the reading of low-frequency inconsistent words, which are words that do not follow standard grapheme-to-phoneme conversion rules (e.g., pint). Pseudowords are read via sub-lexical processes, while inconsistent words require whole-word or semantic processing. Alexia is an acquired reading impairment following brain lesions. Surface alexia is characterized by difficulty in reading inconsistent words. Surface alexia often co-occurs with the semantic variant of Primary Progressive Aphasia (PPA), with atrophy typically starting in the left ATL. Since the ATL is suggested as a semantic hub, it may support reading inconsistent words via semantic access. However, this association is challenged by cases of post-stroke alexia without semantic impairments and semantic impairments in PPA without surface alexia. Moreover, the ATL’s role as a semantic hub remains debated. Methods. Seventy-seven neurotypical participants underwent two High-Definition Transcranial Direct Current Stimulation, corresponding to real and sham stimulation, with the order of stimulation counterbalanced across participants. In the first experiment, we targeted the left ATL while participants performed a Word Naming task involving consistent words, inconsistent words and pseudowords. In a second experiment, participants completed a Picture Plausibility task, making semantic judgments about pictures following the same ATL stimulation. Some pictures represented plausible objects or events, while others depicted implausible objects (e.g., a parrot with duck feet) or events (e.g., an elephant riding a bicycle). In a third experiment, we stimulated the left tempo-occipital cortex (TOC) while participants performed the same Picture Plausibility task. This served as a control experiment, as TOC is hypothesized to be involved in visual-semantic processing and was expected to affect nonverbal semantic processing. We applied linear mixed-effects regression models on Reaction Time, including participant as a random factor, and controlling for variables of no interest (i.e., number of letters, Orthographic neighborhood, frequency, concreteness and valence) as regressors. Results. We conducted a median split to divide words as high-frequency or low-frequency for both consistent and inconsistent categories. In the sham condition, low-frequency inconsistent words were read more slowly than high-frequency inconsistent words. This effect disappeared with ATL stimulation. Furthermore, we found an interaction between consistency and stimulation in the low-frequency subset, but not in the high-frequency subset. More specifically, low-frequency inconsistent words were read more quickly after stimulation, whereas consistent words showed the opposite pattern being read more slowly after stimulation. In the Picture Plausibility task, ATL stimulation showed no effect on the reaction time of nonverbal semantic processing, whereas TOC stimulation significantly increased reaction time. Discussion. These findings support the role of the left ATL in reading inconsistent words, aligning with the presence of surface alexia in the semantic variant of PPA. However, the lack of effect on the non-lexical semantic task suggests that the ATL is likely to be involved in lexical processes rather than purely amodal semantic representation. This is consistent with lesion studies showing dissociation between semantic impairments and surface alexia. These findings clarify previously conflicting result in the literature and elucidate the role of ATL in reading.
Topic Areas: Reading, Language Production