METABRAILLE · A longitudinal MRI study on dual Braille/Visual alphabet readers. Challenging the canonical view of the brain where each sensory modality is processed by a dedicated system (visual, somatosensory…)

A longitudinal MRI study on dual Braille/Visual alphabet readers. Challenging the canonical view of the brain where each sensory modality is processed by a dedicated system (visual, somatosensory...)

Under the current project, we have carried out the planned research on Braille reading in sighted subjects. We also extended the pursuit of the same research questions, namely the mechanisms of large-scale plasticity in the human brain and the division-of-labour in the brain in changing circumstances with additional experiments in deaf and blind subjects. The brain is capable of large-scale reorganization in blindness or after massive injury. Such reorganization crosses the division into separate sensory cortices (visual, somatosensory...). As its result, the visual cortex of the blind becomes active during tactile Braille reading. At the onset of ours research, there were two outstanding questions regarding this kind of large-scale reorganization. First, although the possibility of such reorganization in the normal, adult brain has been raised, definitive evidence has been lacking. Second, most of the data available was from the visual cortex – almost no data was available from other cortices, notably the auditory cortex. In our experiments, we first demonstrated that such extensive reorganization is possible in normal, sighted adults who learned Braille while their brain activity was investigated with fMRI and Transcranial Magnetic Stimulation (TMS) (Bola et al., 2016; Siuda-Krzywicka et al., 2016) (all pdfs available at http://www.szwedlab.psychologia.uj.edu.pl/pub ). Subjects showed enhanced activity for tactile reading in the visual cortex, including the Visual Word Form Area (VWFA) that was modulated by their Braille reading speed and strengthened resting-state connectivity between visual and somatosensory cortices. Moreover, TMS disruption of VWFA activity decreased their tactile reading accuracy. Our results indicate that large-scale reorganization is a viable mechanism recruited when learning complex skills. In a satellite project, we also demonstrated that learning Braille in the visual domain is unusually slow, prone to errors and highly serial, even in Braille readers with years of prior reading experience. This is in stark contrast to Cyrillic, a natural script, where only 3 months of learning sufficed to achieve relative proficiency. This suggest that visual features such as line junctions and their combinations might be necessary for efficient reading (Bola, Radziun, et al., 2017). We have also conducted additional experiments in the blind (Raczy et al., 2017, Society for Neurobiology of Language abstract). Second, as most of the data on the subject was available was from the visual cortex – almost no data was available from other cortices, notably the auditory cortex, we carried out a series of experiments in deaf subjects that probed task-specific reorganization of the auditory cortex for visual rhythm perception (Bola, Zimmermann, et al., 2017; Szwed, Bola, & Zimmermann, 2017). Auditory areas can become recruited for visual and tactile input following deafness. While non-human data suggests that this reorganization might be task-specific, human evidence has been lacking. Here we enrolled 15 deaf and 15 hearing adults into an fMRI experiment, during which they discriminated between temporally complex sequences of stimuli (rhythms). Both deaf and hearing subjects performed the task visually, in the central visual field. In addition, hearing subjects performed the same task in the auditory modality. We found that the visual task robustly activated the auditory cortex in deaf subjects, peaking in the posterior-lateral part of high-level auditory areas. This activation pattern was strikingly similar to the pattern found in hearing subjects performing the auditory version of the task. Whereas performing the visual task in deaf subjects induced an increase in functional connectivity between the auditory cortex and the dorsal visual cortex, no such effect was found in hearing subjects. We conclude that the high-level auditory cortex in the deaf switches its input modality from sound to vision but preserves its task-specific activation pattern independent of input modality. Task-specific reorganization might thus be a general principle that guides cortical plasticity in the brain. The work done under this grant has been recognized with national awards (in 2016, National Science Center prize for Marcin Szwed ; in 2017, Konorski prize for best neuroscience paper for Siuda-Krzywicka et al., 2016, eLife). It has been featured in national and international media (http://www.szwedlab.psychologia.uj.edu.pl/en_GB/in-the-media). The grant was of enormous help in establishing and stabilizing my research team (http://www.szwedlab.psychologia.uj.edu.pl) . It was also a career springboard for two young researchers employed in it. Katarzyna Siuda-Krzywicka went on to pursue her PhD at the École des Neurosciences de Paris Île-de-France (http://www.paris-neuroscience.fr/en/katarzyna-siuda-krzywicka) , while Łukasz Bola (http://lobi.nencki.gov.pl/team/6/) , upon competition of his PhD, will continue his research at the Cognitive Neuropsychology Lab at Harvard (http://www.wjh.harvard.edu/%7Ecaram/index.html).

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