P220 Cortical time course of reading processing by navigated transcranial magnetic stimulation

Abstract

Introduction The time scale at which reading processes operate is matter of intense debate. Chronometric TMS studies can be used to understand the global reading as well as temporal coordinates of sub processes involved in word reading. Objectives The aim of our TMS study was to investigate timing of cortical areas involvement in process of reading words in healthy subjects. The study was designed to provide timing of activity in predefined cortical areas involved in reading aloud as a global process. Materials and Methods Twelve healthy and right-handed volunteers (6 men, mean age 29.67 ± 9.82 years, and 6 females, mean age 28 ± 5.8 years) underwent patterned protocol of rTMS over the specific brain areas related to reading process identified intraoperatiely, namely to: posterior part of superior temporal gyrus (PSTG), posterior part of middle temporal gyrus (PMTG), left supramarginal gyrus (SMG), angular gyrus (AnG), and posterior part of inferior frontal gyrus (opercular part of Broca’s area) (OpIFG), while participants were reading words (overt reading of presented words). Modified patterned rTMS stimulation protocol consisted of 4 bursts of 4 stimuli each, with an interstimulus interval of 6 ms, and a burst repetition rate of 4 Hz. The rTMS protocol was applied at four time points: 150–175–200 ms, 225–250–275 ms, 300–325–350 ms, 400–425–450 ms) following word presentation, including the 0 ms as the control condition. Results While stimulating OpIFG the reading latency was significantly prolonged for time point of 300–325–350 ms (F(1) = 9.2, p = .0) compared to control time condition. Stimulation of PSTG and PMTG revealed a significantly prolonged reading latencies for time points of 300–325–350 (PSTG: F(1) = 5.1, p = .0; PMTG: F(1) = 8.6, p = .0) and 400–425–450 ms (PSTG: F(1) = 26.1, p = .0; PMTG: F(1) = 11.1, p = .0) compared to control. When stimulating AnG reading latency significantly increased for time points of 150–175–200 ms (F(1) = 6.5, p = .0), 300–325-350 (F(1) = 8.9, p = .0) and 400–425–450 ms (F(1) = 7.6, p = .0) compared to control. Stimulation of SMG did not reveal significant differences when comparing time points and control condition. Conclusion Our results document significant effect on word reading latency during application of modifed rTMS on OpIFG, PSTG, PMTG, and AnG in healthy subjects. The results of this study might be used in upgrading/constructing theoretical models of reading and assessing functional connectivity between brain regions involved in reading process.