The role of the left inferior parietal lobule in reading.

One of the regions that have consistently been included in the neurological models of reading is the left inferior parietal lobule (IPL), however, the precise functional and temporal contributions of this region to reading have not yet been fully established. There are three hypotheses concerning IPL contributions to visual word recognition. The first one claims that the IPL is the site of stored visual word forms although it remains unclear whether these are stored in supramarginal (SMG) or angular (ANG) fields of the IPL. The second hypothesis argues that the procedures for converting spelling-to-sound are a function of the IPL, but it is unclear whether these are specifically located in SMG or ANG, or both. Finally, a third hypothesis suggests that SMG and ANG preferentially contribute to phonological and semantic processing of written words, respectively. In this thesis, I empirically evaluated these hypotheses using repetitive transcranial magnetic stimulation (rTMS) to temporarily and selectively disrupt processing in left SMG and ANG during visual word recognition and measure the effect on reading behaviour. I also investigated the time course of SMG and ANG involvement to visual word recognition using double-pulse TMS. My research demonstrates that SMG contributes preferentially to phonological aspects of word processing and the processing begins early and over a sustained period of time (between 80 to 200 msec post-stimulus onset). ANG contributes preferentially to semantic aspects of word processing but the temporal dynamics of this contribution were not successfully revealed in this thesis and require further investigation. In addition, I empirically evaluated the efficiency of using functional magnetic resonance (fMRI) and TMS to functionally localize a target site for TMS experiments. I demonstrated that both methods are similarly accurate in identifying stimulation site but neither of them is 100% accurate