Preliminary evidence of prolonged timing effects of theta-burst stimulation in the reading system.

Theta-burst stimulation (TBS) is a repetitive transcranial magnetic stimulation technique that can be used to upregulate or downregulate different brain regions. However, the timing of its effects and the differing effects of continuous TBS (cTBS) versus intermittent TBS (iTBS) in the reading system have not been explored. This study assessed how stimulation type and post-stimulation timing affected change in performance during a phonological discrimination and sight word recognition task after stimulation of supramarginal gyrus (SMG). Fourteen right-handed young adults (age 18-27 years; 44% male) were block-randomized to receive either iTBS or cTBS to the supramarginal gyrus. Participants then performed a pseudoword discrimination task and an orthographic awareness task (behavioral control) at four different time points and change in reaction time compared to baseline was measured from each time point. There was no effect of stimulation type on change in reaction time [t(16) = -0.2, p = 0.9], suggesting that both types of TBS caused similar effects. Percent change in reaction time decreased over time in the pseudoword task [t(50) = -5.9, p < 0.001], indicating faster pseudoword processing speed with better performance 60-70 min after stimulation. In contrast, no change was demonstrated over time for the behavioral control task [t(43) = -0.6, p = 0.6], suggesting that the change over time seen in the test condition was not a learning effect. These findings provide insight into the effects of TBS on the reading system and can guide future study designs.

The Impact of Transcranial Magnetic Stimulation on Reading Processes: A Systematic Review.

The current systematic review examines the behavioral effects of TMS on reading. Transcranial magnetic stimulation (TMS) to targeted nodes of the brain's reading network has been shown to impact reading. Extracted data included (a) study characteristics, (b) methodology, (c) targeted nodes, (d) control paradigm, (e) type of reading task, (f) adverse effects, and (g) main findings. Data was classified by type of reading task: 1) phonological processing, 2) semantic judgment, 3) lexical decision, 4) whole word reading, and 5) visual or text characteristics. Seventy records from 46 studies (n = 844) were identified. Results indicate that TMS modulates semantic judgments when focused in the anterior aspects of the reading circuit, phonological processes after stimulation within the dorsal circuit, and impacts single word recognition and contextual reading when administered to the ventral circuit. Findings suggest that changes in specific behavioral aspects of reading following TMS may contribute to identification of foci for use as part of reading interventions.

Left hemisphere specialization for word reading potentially causes, rather than results from, a left lateralized bias for high spatial frequency visual information.

There is considerable evidence showing that efficient visual word recognition relies on high spatial frequency (HSF) visual coding in the left posterior fusiform gyrus. But whether the bias for HSF in the left hemisphere (LH) causally contributes to the LH superiority for word recognition or possibly results from it remains unknown. To assess whether the lateralization for HSF information exists prior to the left lateralization for reading, we used a divided-visual field task to examine the LH bias for orthographic processing and for HSF Gabor patches in young children (mean age 4.5 years) with variable letter knowledge, and in adults. If LH specialization for orthographic processing results from a pre-existing HSF bias in the LH, then LH specialization for HSF information should be evident even in those young children with minimal, if any, letter knowledge. The adult participants showed the predicted LH lateralization for both HSF information and word recognition. Neither of these hemispheric biases, however, was statistically significant in the group of young children. Further investigation, however, revealed a correlation between these biases such that those children with the somewhat more developed LH advantage for orthographic representations also evinced an LH bias for HSF information. These findings suggest that, rather than serving as a precursor for the LH superiority for word recognition, the LH bias for HSF input might emerge in concert with it or potentially even be a consequence of the acquisition of orthographic competence.