Slide Slam S11 Sandbox Series
The roles of blind “visual” cortex in language processing: insights from fMRI and TMS studies
Jacek Matuszewski1, Łukasz Bola2, Katarzyna Jednoróg1, Olivier Collignon3,4, Artur Marchewka1; 1Nencki Institute of Experimental Biology, Polish Academy of Sciences, 2Institute of Psychology, Polish Academy of Sciences, 3Center for Mind/Brain Studies, University of Trento, Trento, Italy, 4Institute for research in Psychology (IPSY) and Neurosciences (IoNS), UC Louvain
Neuroplasticity is characterised by functional and anatomical brain reorganisation driven by environmental demands. It occurs in response to experiences like sensory deprivation or intensive training and can cross boundaries between the senses. For example, the visual cortex of blind subjects can respond to tactile or auditory stimuli in a functionally specific fashion. Recent results suggest that reorganisation could be also observed in sighted subjects after demanding learning, raising the question about sensory-dependence of the brain organisation. In the current study we are investigating the role of the “visual” cortex of sighted and early blind people in reading from touch using the Braille system. First, using fMRI, we characterised brain responses to tactile word reading (experimental condition) and nonsense Braille (control condition) in congenitally blind (N = 18; age M = 34.4; SD = 7.5) and trained sighted (N = 26; age M = 23.1; SD = 3.4) subjects. Whole-brain comparisons revealed that tactile reading engaged the left inferior frontal gyrus (IFG) and ventral occipito-temporal cortex in both groups. However, reading meaningful Braille, when compared to the control condition, elicited activity in the early “visual” cortex selectively in the congenitally blind subjects. This enhanced V1 activity could not be explained by the higher tactile reading proficiency of blind subjects. Furthermore, psycho-physiological interaction analysis showed stronger functional connectivity between left IFG and V1 in the blind during the experimental condition, indicating possible reading-specific coupling between deprived visual cortex and language network. In the next stage of the project that we are currently carrying out, we are investigating temporal interactions between V1 and the visual word form area (VWFA). With the chronometric transcranial magnetic stimulation (TMS) which enables to causally trace the hierarchy between targeted brain regions, we are examining the information flow between low-level and higher-order visual areas during reading and speech processing in blind and sighted subjects. We plan to use 20 Hz repetitive TMS to temporarily disrupt neuronal processing in V1 and the VWFA. Pulses will be delivered in “early” (50-150 ms) and “late” (150-250 ms) time windows during lexical decision tasks performed aurally and tactually (blind subjects) or visually (sighted subjects). This experimental design allows us to trace linguistic processing in the visual cortex and its dependence on the sensory modality. TMS disruption during reading and speech processing observed first in VWFA and then in V1 could indicate that the deprived visual cortex performs linguistic computations occurring after orthographic analysis. Inversely, information flow from V1 to VWFA could support the view in which V1 retains its specialisation towards simple spatial processing of sound and touch, which is then followed by orthographic analysis occurring in the VWFA. In conclusion, with the combination of multiple state-of-the-art neuroimaging methods, the present project aims to investigate whether the blind visual cortex responds differently to (tactile) reading and speech processing. In conjunction with our previous findings, results of this study should contribute to a deeper understanding of the nature of the blind visual cortex in the context of currently discussed theoretical frameworks.