The Diversity of Early Visual Cortex Layout: Five Patterns and Hemispheric Asymmetry
Poster No:
1706
Submission Type:
Abstract Submission
Authors:
Mark Schira1, Ruby Barahona1, Noah Benson2, Fernanda Ribeiro3
Institutions:
1University of Wollongong, Wollongong, NSW, 2University of Washington, Seattle, WA, 3Justus-Liebig University Giessen, Giessen, Hessen
First Author:
Co-Author(s):
Introduction:
Retinotopic maps of early visual cortex (EVC) have been studied for decades in both humans and non-human primates using various techniques. These studies have proposed a canonical layout of early visual areas: V1 represents a continuous hemifield, while V2 and V3 are divided into dorsal and ventral portions for the lower and upper visual field representations, respectively. These quarterfields converge at the foveal confluence, where V2 and V3 form U-shaped bands around V1 [1, 2, 3].
This canonical layout is generally considered symmetric between hemispheres, with each hemisphere mapping the contralateral visual field. While this hemispheric symmetry has been well-documented in humans, challenges to this model remain, particularly in cross-species comparisons [3, 4]. Within humans, individual differences in EVC maps have traditionally been interpreted as variations in size [2, 5], with limited attention paid to variability in structural layout. Moreover, the assumption of hemispheric symmetry has typically gone unquestioned, partly due to the small sample sizes of retinotopic mapping studies (5–12 participants in humans and 2–4 in non-human primates).
Using the 7 Tesla Human Connectome Project (HCP) retinotopy dataset [6], Ribeiro et al. (2023) found greater variability inter-subject variability in the left hemisphere [7]. Additionally, they identified a non-canonical Y-shaped discontinuity in the early visual cortex layout in several participants, challenging the assumption of a uniform layout. Here we investigate variability by clustering EVC maps into distinct categories.
This canonical layout is generally considered symmetric between hemispheres, with each hemisphere mapping the contralateral visual field. While this hemispheric symmetry has been well-documented in humans, challenges to this model remain, particularly in cross-species comparisons [3, 4]. Within humans, individual differences in EVC maps have traditionally been interpreted as variations in size [2, 5], with limited attention paid to variability in structural layout. Moreover, the assumption of hemispheric symmetry has typically gone unquestioned, partly due to the small sample sizes of retinotopic mapping studies (5–12 participants in humans and 2–4 in non-human primates).
Using the 7 Tesla Human Connectome Project (HCP) retinotopy dataset [6], Ribeiro et al. (2023) found greater variability inter-subject variability in the left hemisphere [7]. Additionally, they identified a non-canonical Y-shaped discontinuity in the early visual cortex layout in several participants, challenging the assumption of a uniform layout. Here we investigate variability by clustering EVC maps into distinct categories.
Methods:
This project is based on the Human Connectome Project 7T retinotopy dataset with 182 (109 females, 22-35 years) high-resolution structural and functional data [6]. The dataset was visualized using Connectome Workbench 2.0.0. Polar angle maps and eccentricity maps for each participant were visualized using the RGRBR_mirror90_pos metric palette.
Manual classification of polar angle maps for all participants and hemispheres was conducted by a student trained by two neuroanatomy experts. EVC layout was traced with dots marking key points across polar angle, eccentricity and field sign maps. Each hemisphere, left and right independently, was categorized into one of five clusters: 'Canonical,' 'Similar to Canonical,' 'Incomplete Dorsal,' 'No Structure,' and 'Y-Shape'. Counts can be seen in Figure B. For each cluster average polar angle gradients was calculated (Figure A).
Manual classification of polar angle maps for all participants and hemispheres was conducted by a student trained by two neuroanatomy experts. EVC layout was traced with dots marking key points across polar angle, eccentricity and field sign maps. Each hemisphere, left and right independently, was categorized into one of five clusters: 'Canonical,' 'Similar to Canonical,' 'Incomplete Dorsal,' 'No Structure,' and 'Y-Shape'. Counts can be seen in Figure B. For each cluster average polar angle gradients was calculated (Figure A).
Results:
A distinct Y-shaped pattern was identified in the dorsal portion of several participants. McNemar's tests revealed that Y-shapes were significantly more frequent in the left hemisphere (23 vs. 7), while "Canonical" layouts were significantly more frequent in the right hemisphere (121 vs. 85). Hemispheric asymmetry was not linked to handedness; a linear regression confirmed no influence of handedness scores or cluster categories on hemispheric asymmetry.
Conclusions:
The results highlight notable intersubject variability in early visual cortex layout. While the canonical layout remains the most frequent pattern (204 of 362 hemispheres), the presence of a specific non-canonical pattern (e.g., Y-shaped configurations) in 30 hemispheres suggests these non-canonical layouts are meaningful alternate patterns rather than accidental variations. Such within species variability will arguably confound cross species comparisons with small n.
Notably, the hemispheric asymmetry identified here does not manifest itself as a different canonical pattern between the left and right, but instead in different frequencies of patterns between the left and right visual cortices. The distribution asymmetry was not related to handedness score, suggesting that interhemispheric variability stems from structural variation rather than functional dominance [7]. However, the underlying explanation for hemispheric asymmetry remains unclear and warrants further investigation.
Notably, the hemispheric asymmetry identified here does not manifest itself as a different canonical pattern between the left and right, but instead in different frequencies of patterns between the left and right visual cortices. The distribution asymmetry was not related to handedness score, suggesting that interhemispheric variability stems from structural variation rather than functional dominance [7]. However, the underlying explanation for hemispheric asymmetry remains unclear and warrants further investigation.
Modeling and Analysis Methods:
Activation (eg. BOLD task-fMRI) 2
Neuroanatomy, Physiology, Metabolism and Neurotransmission:
Anatomy and Functional Systems 1
Perception, Attention and Motor Behavior:
Perception: Visual
Keywords:
Data analysis
FUNCTIONAL MRI
Perception
Vision
Other - Retinotopy
1|2Indicates the priority used for review
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[2] Benson N C, Yoon J M D, Forenzo D, Engel S A, Kay K N, Winawer J (2022), “Variability of the surface area of the V1, V2, and V3 maps in a large sample of human observers,” The Journal of Neuroscience, vol. 42, no. 46, pp. 8629-8646, https://doi.org/10.1523/JNEUROSCI.0690-21.2022
[3] Rosa M G P (2002), “Visual maps in the adult primate cerebral cortex: some implications for brain development and evolution,” Brazilian Journal of Medical and Biological Research, vol. 35, no. 12, pp. 1485-1498, https://doi.org/10.1590/s0100-879x2002001200008
[4] Angelucci A, Roe A W, Sereno M I (2015) “Controversial issues in visual cortex mapping: Extrastriate cortex between areas V2 and MT in human and nonhuman primates,” Visual Neuroscience, vol. 32, pp. E025-E025, https://doi.org/10.1017/S0952523815000292
[5] Schira, Mark M., Alex R. Wade, and Christopher W. Tyler. "Two-dimensional mapping of the central and parafoveal visual field to human visual cortex." Journal of neurophysiology 97.6 (2007): 4284-4295.
[6] Benson N C, Jamison K W, Arcaro M J, Vu A T, Glasser M F, Coalson T S, Van Essen D C, Yacoub E, Ugurbil K, Winawer J, Kay K (2018), “The Human Connectome Project 7 Tesla retinotopy dataset: Description and population receptive field analysis,” Journal of Vision (Charlottesville, Va.), vol. 18, no. 13, pp. 23-23, https://doi.org/10.1167/18.13.23
[7] Ribeiro F L, York A, Zavitz E, Bollmann S, Rosa M G P, & Puckett A (2023), “Variability of visual field maps in human early extrastriate cortex challenges the canonical model of organisation of V2 and V3,” eLife, vol. 12, https://doi.org/10.7554/eLife.86439
[8] Ribeiro F L, York A (2023), “VariabilityEarlyVisualCortex,” https://archive.softwareheritage.org/swh:1:dir:fd3f6776298b8f1e63623dfb95fe2107d9d8a573