Functional Connectivity Asymmetries in Relation to Functional Lateralization

Human brains consist of two hemispheres that typically differ in their specialization for cognitive functions, indicated by an increased activity in one hemisphere compared to another while performing a task related to a specific cognitive function. In the majority of individuals, the left hemisphere predominantly supports language and praxis, whereas the right hemisphere is more involved with visuospatial attention. Beyond functional asymmetries, hemispheric asymmetries have also been observed in functional connectivity. More specifically, Gotts et al. (2013) argued that (regions in) the left hemisphere interact more exclusively with regions within the same hemisphere, while (regions in) the right hemisphere tend to interact more with both hemispheres. These observations have led to theories proposing that asymmetries in inter- and intrahemispheric functional connectivity play a mechanistic role in shaping or supporting the typical lateralization profile (i.e., left-lateralized language and praxis, right-lateralized visuospatial attention). However, a substantial subset of the population displays atypical lateralization patterns, and the relationship between such patterns and hemispheric connectivity asymmetries remains largely unexplored. The core idea that guides the current investigation states that if connectivity asymmetries play a fundamental role in functional lateralization, then individuals with a reversed typical lateralization profile should also exhibit a corresponding reversed connectivity asymmetry. All data used for the current project was previously collected by Gerrits et al. (2020). Resting-state fMRI data will provide inter- and intrahemispheric connectivity measures, and task-based fMRI data will yield whole-hemisphere lateralization indices for three functions (i.e., language, praxis, visuospatial attention). Participants will be classified as typical or reversed typicals (i.e., a complete mirror reversal of the typical pattern) based on the whole-hemisphere lateralization indices. Using the resulting dataframe, the present preregistered study will attempt to conceptually replicate the proposed connectivity asymmetries at both a global hemispheric and a regional level and test whether reversed typicals show a reversed pattern in order to assess the likelihood that this asymmetry is related to individual differences in functional lateralization. References: Gerrits, R., Verhelst, H., & Vingerhoets, G. (2020). Mirrored brain organization: Statistical anomaly or reversal of hemispheric functional segregation bias? Proceedings of the National Academy of Sciences, 117(25), 14057–14065. https://doi.org/10.1073/pnas.2002981117 Gotts, S. J., Jo, H. J., Wallace, G. L., Saad, Z. S., Cox, R. W., & Martin, A. (2013). Two distinct forms of functional lateralization in the human brain. Proceedings of the National Academy of Sciences, 110(36). https://doi.org/10.1073/pnas.1302581110 Gerrits R, Vingerhoets G. The reliability of bilateral cerebral laterality for word generation: Who is left in the middle? Imaging Neurosci (Camb). 2025 Aug 7;3:IMAG.a.102. doi: 10.1162/IMAG.a.102. PMID: 40800965; PMCID: PMC12336058.