Mapping curvature domains in human V4 using CBV-sensitive layer-fMRI at 3T

Elisa Zamboni ^1,2* Isaac Watson ^2,3 Rüdiger Stirnberg ⁴ Laurentius Huber ⁵ Elia Formisano ⁶ Rainer Goebel ⁶ Aneurin J Kennerley ⁷ Antony B Morland ^2,8,9

• ¹ School of Psychology, Faculty of Science, University of Nottingham, Nottingham, United Kingdom
• ² York Neuroimaging Centre, University of York, York, UK, York, United Kingdom
• ³ Leeds Institute of Cardiovascular and Metabolic Medicine, Faculty of Medicine and Health, University of Leeds, Leeds, England, United Kingdom
• ⁴ German Center for Neurodegenerative Diseases, Helmholtz Association of German Research Centers (HZ), Bonn, North Rhine-Westphalia, Germany
• ⁵ National Institutes of Health (NIH), Bethesda, Maryland, United States
• ⁶ Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, Netherlands, Netherlands
• ⁷ Department of Sport and Exercise Sciences, Faculty of Science and Engineering, Manchester Metropolitan University, Manchester, North West England, United Kingdom
• ⁸ Department of Psychology, Faculty of Sciences, University of York, York, England, United Kingdom
• ⁹ York Biomedical Research Institute, Faculty of Sciences, University of York, York, United Kingdom

Introduction: A full understanding of how we see our world remains a fundamental research question in vision neuroscience. While topographic profiling has allowed us to identify different visual areas, the exact functional characteristics and organisation of areas up in the visual hierarchy (beyond V1 & V2) is still debated. It is hypothesised that visual area V4 represents a vital intermediate stage of processing spatial and curvature information preceding object recognition. Advancements in magnetic resonance imaging hardware and acquisition techniques (e.g., non-BOLD functional MRI) now permits the capture of cortical layer-specific functional properties and organisation of the human brain (including the visual system) at high precision. Methods: Here, we use functional cerebral blood volume measures to study the modularity in how responses to contours (curvature) are organised within area V4 of the human brain. To achieve this at 3 Tesla (a clinically relevant field strength) we utilise optimised high-resolution 3D-Echo Planar Imaging (EPI) Vascular Space Occupancy (VASO) measurements. Results: Data here provide the first evidence of curvature domains in human V4 that are consistent with previous findings from non-human primates. We show that VASO and BOLD tSNR maps for functional imaging align with high field equivalents, with robust time series of changes to visual stimuli measured across the visual cortex. V4 curvature preference maps for VASO show strong modular organisation compared to BOLD imaging contrast. It is noted that BOLD has a much lower sensitivity (due to known venous vasculature weightings) and specificity to stimulus contrast. We show evidence that curvature domains persist across the cortical depth. The work advances our understanding of the role of mid-level area V4 in human processing of curvature and shape features. Impact: Knowledge of how the functional architecture and hierarchical integration of local contours (curvature) contribute to formation of shapes can inform computational models of object recognition. Techniques described here allow for quantification of individual differences in functional architecture of mid-level visual areas to help drive a better understanding of how changes in functional brain organisation relate to difference in visual perception.