Higher order visual areas in the mouse may be better classified as a single area V2

A) The currently accepted organization of the mouse visual system includes multiple higher order visual areas beyond V1, defined based on reversals in the progression of the visual field, each with partial and biased coverage of the visual field. Projection pattern figure is modified from (Wang & Burkhalter, 2007b) and partial visual field coverage is modified from (Zhuang et al., 2017). B) New evidence of visual field reversals within single areas in the tree shrews (Sedigh-Sarvestani et al., 2021), and marmosets (H.-H. Yu et al., 2020) challenge the parcellation of higher order visual cortex in the mouse. C) Instead, we propose a new view supports a new view wherein a single area V2, with full coverage of the visual field, borders V1 in the mouse. D) This would make the organization of the mouse visual cortex like that in most other mammals, exhibiting an area V1 adjacent to a single area V2. Modified from (Rosa & Krubitzer, 1999)

Retinotopic models show emergence of a single complex map of visual space beyond mouse V1

We extended the elastic net model from previous work (Sedigh-Sarvestani et al., 2020) to constrain a model of V2 to the unique structure of the mouse. A) Borders of cortical space were traced from (Zhuang et al., 2017) and a teardrop shaped visual field was used to approximate the full visual field covered by mouse V1. B-C) Modifying the constraints to smoothness and isotropy result in internal reversals, seen in alternating field sign (Sereno et al., 1994). D) Visualization of the visual field, azimuth & elevation planes, covered by normal lines between the V1 and higher order visual area border as in right of A. These lines are stacked on the Z-axis, and color coded, going from the caudal border of V1 in purple around the circumference of V1 to the medial edge in orange. E) This complex retinotopy generates, from a single continuous area, reversals that approximately match mouse higher order visual areas, showing that previously reported retinotopic maps in mouse higher order visual areas are parsimonious with a single area covering a full, but twisted, visual field. F) Matching points in the visual field with their locations in this single area, creates similar patterns to what has been shown in tracer studies (Wang & Burkhalter, 2007a), compare 1A.

Retinotopy accounts for functional variations between higher order areas in mouse visual cortex

A) Map of motion sensitivity adapted from (Sit & Goard, 2020) showing higher sensitivity in the lower field representation of V1 and higher order visual areas. B) Dorsal and Ventral streams in the mouse containing multiple higher order visual areas have been suggested due to differences in function, however these maps closely align onto elevation axis of retinotopy. Figure made using data from (Zhuang et al., 2017) C) Behavioral encoding as a function of cortical space shows large change along the V1 border, but not between higher order visual areas (Minderer et al., 2019). Scale bar 1mm. D) Schematic of eccentricity from focea with area estimates for the data used in F&G.E) Schematic of retinal cone opsin gradient following (Demb & Singer, 2015). F) Data from (Han et al., 2022). Tuning to spatial frequency (SF) of bandpass cells in each area (left), plane fit of SF to area elevation and eccentricity from focea (middle) and the residuals (right) after subtracting a plane fit. G) Same for temporal frequency (TF). Area tuning violin plots show the distribution of tuning within areas with white dots for the mean and lines for 95% confidence interval.

Complex retinotopy beyond V1 is a common feature of secondary visual cortex in multiple species

A) Retinotopy maps in mouse V1, schematics created based on data from (Zhuang et al., 2017). Currently accepted area delineations shown in blue box. B) Retinotopic maps in tree shrew visual cortex. Data from (Sedigh-Sarvestani et al., 2021). C) Retinotopic maps in ferret visual cortex. Data from (Manger et al., 2002a). D) Schematic of retinotopic maps in visible portion of macaque V1 and V2. Data from (Roe & Ts’o, 1995b; Shipp & Zeki, 2002b). Color maps are different for each species and are simply meant to indicate relatively more central or peripheral regions of the visual field.