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The causal role of left inferior frontal gyri in Chinese character handwriting: A transcranial magnetic stimulation study
Poster Session C, Friday, October 25, 4:30 - 6:00 pm, Great Hall 3 and 4
Yichi ZHANG1, Xufeng DUAN1, Joseph DEVLIN2, Zhenguang CAI1; 1The Chinese University of Hong Kong, 2University College London
Objective: Producing written words involves central processes such as orthographic retrieval from long-term memory (LTM), phonology-orthography conversion (POC) and holding orthographic information in the working memory, together with peripheral processes such as allographic/letter shape selection and graphic-motor planning. Previous fMRI studies suggest that the left inferior frontal gyrus (LIFG) is related to retrieving orthographic representations. However, it remains unclear whether the LIFG plays a causal role in central orthographic processing, such as retrieving orthography from long-term memory during simplified Chinese character handwriting, and whether inhibiting the LIFG would disrupt this process. Therefore, we set out to answer these questions by administering the transcranial magnetic stimulation with the inhibitory repetitive TMS (rTMS) protocol over LIFG to assess the behavioral changes of simplified Chinese orthographic processing. Methods: 20 healthy adults native to simplified Chinese underwent this within-subject offline TMS experiment, composed of a handwriting following offline rTMS to LIFG and another handwriting session following offline rTMS to the vertex (as a control site). The rTMS protocol used the stimulation frequency of 1 Hz, lasting for a duration of 20 minutes (1200 pulses in total). The order of the two stimulations was counter-balanced across participants and the two sessions were separated with an interval of about 25 min. After offline rTMS in a session, participants wrote 60 Chinese simplified characters one by one according to a dictation prompt (e.g., 灶台的灶, “the character 灶 in the word 灶台”), with a total of 120 characters over the two sessions. In a handwriting trial, participants first heard a dictation prompt, wrote down the target character. After handwriting, participants were shown the target character and reported whether they had correctly written the target character, did not know what character to write, or knew what character to write but could not (fully) write it. We collected three behavioral measures: handwriting latency (from the offset of the dictation prompt to the onset of handwriting) as a measure orthographic retrieval, handwriting duration (from the onset to the offset of handwriting) as a measure of the cascading central and peripheral processes of handwriting, and handwriting accuracy (proportion of accurate handwriting in the self-reports) as a measure of participant’s success in orthographic retrieval. Results & Discussion: We observed an inhibitory effect of offline rTMS on handwriting latency (but not on handwriting duration): Participants needed longer times to initiate handwriting after hearing a dictation prompt after receiving offline rTMS on LIFG than on the vertex. The findings that disrupting LIFG led to elevated handwriting latencies but not elevated durations suggest that LIFG is casually involved in the retrieval of orthographic representations (but not in the execution of peripheral processes of handwriting). We also observed no offline rTMS effect on handwriting accuracy, which may suggest that though the offline rTMS we applied impacted orthographic retrieval, it was not strong enough to lead to failure of orthographic retrieval. In conclusion, this study demonstrated that LIFG plays a causal role as a core orthographic region supporting complex orthographic processes across languages.
Topic Areas: Writing and Spelling, Disorders: Acquired