Presentation
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Left-Right Asymmetries of Sulcal Patterns in and around Broca’s Area
Poster A114 in Poster Session A, Tuesday, October 24, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
This poster is part of the Sandbox Series.
Martin Wegrzyn1, Rachel Bruneman2, Sarah Franke1, Alina Mersch1, Marie Plän1, Johanna Kissler1,3; 1Department of Psychology, Bielefeld University, Germany, 2Faculty of Medicine, Ruhr-University Bochum, Germany, 3Center for Cognitive Interaction Technology, Bielefeld, Germany
Language is one of the most strongly lateralized functions in the human brain, and for the vast majority of individuals, the left hemisphere is dominant for language. Especially in the context of presurgical planning, the dominant hemisphere needs to be determined using activation (fMRI) or disruption (Wada-test) methods, so that cases with atypical lateralization can be identified. From a practical but also a basic science perspective, additional markers for assessing language dominance are desirable. In this regard, the macroanatomical structure of the cortex is an obvious but contested candidate. In the present study, our goal was to identify differences between the two hemispheres solely in terms of the structure of their sulci. We assessed to what degree their presence or absence, their position, orientation, shape and configuration were diagnostic for identifying if a hemisphere belonged to the left or right side. We defined sulci by hand, tracing them on lateral views of the native pial surfaces of 50 healthy right-handed participants from the “Narratives” data set (Nastase et al. 2021). Three raters were presented with 100 hemispheres, which were all oriented to the left side, therefore blinding raters regarding the true side. To increase the reliability of the manual definitions, we required that sulcus tracings overlapped in at least two out of three raters. The overall presence and absence of each sulcus was expressed in simple counts. Mass-univariate analyses (pixel-by-pixel) were used to map fine-grained differences in the sulci’s locations, orientation and shape. Euclidean transforms (shift and rotation) of sulci provided a metric for their similarity regarding position and orientation. Multivariate pattern analyses used the configuration of all sulci to predict if two hemispheres belonged to the same side. In terms of overall presence, the Diagonal Sulcus within Broca’s area was more frequently found in the left hemisphere. The Ascending and Horizontal Rami (AALF and HALF) in Broca’s area showed a tendency to be located more anteriorly and inferiorly on the left side, and the Sylvian Fissure’ shape had a flatter progression towards it posterior end point. When classifying hemispheres by their similarity (a held-out hemisphere with unknown lateralization was assigned to the side it was most similar to in the unblinded training set), we were able to correctly assign 75 out of 100 hemispheres and 47 out of 50 hemisphere pairs to their respective sides. In conclusion, the position of the Ascending and Horizontal Rami and the presence of the Diagonal Sulcus might be particularly important for determining language lateralization, as they showed left-right differences and are located within language-relevant parts of the brain. However, the shape of the Sylvian Fissure is arguably the best general indicator of left-right differences. In future work, the sulcal folding patterns should be related to fMRI data, to test if intrahemispheric variations in sulcal patterns can predict the location of language-related functional regions. The long-term goal of identifying the language-dominant hemisphere - regardless of whether it is located on the left side - will require to work with samples of atypically lateralized individuals.
Topic Areas: Methods, Language Production