Functional specialization of seven mouse visual cortical areas

Abstract

To establish the mouse as a genetically tractable model for high-order visual processing, we characterized fine-scale retinotopic organization of visual cortex and determined functional specialization of layer 2/3 neuronal populations in seven retinotopically identified areas. Each area contains a distinct visuotopic representation and encodes a unique combination of spatiotemporal features. Areas LM, AL, RL, and AM prefer up to three times faster temporal frequencies and significantly lower spatial frequencies than V1, while V1 and PM prefer high spatial and low temporal frequencies. LI prefers both high spatial and temporal frequencies. All extrastriate areas except LI increase orientation selectivity compared to V1, and three areas are significantly more direction selective (AL, RL, and AM). Specific combinations of spatiotemporal representations further distinguish areas. These results reveal that mouse higher visual areas are functionally distinct, and separate groups of areas may be specialized for motion-related versus pattern-related computations, perhaps forming pathways analogous to dorsal and ventral streams in other species.

Figure 1. Retinotopic organization of mouse visual cortex measured with intrinsic signal imaging

Retinotopic organization of cortex mapped in spherical coordinates. Colors indicate angular position in degrees of a drifting bar stimulus that elicited a hemodynamic response at each cortical location (Figure S1 and Movie S1 and S2). (A) Continuous vertical retinotopy map. Positive values above the horizontal meridian, located at ~20° altitude (blue), indicate the upper visual field. (B) Contour lines of vertical eccentricity, with 10° spacing. (C) Overlay of continuous vertical retinotopy map (as in (A)) with altitude contours (solid lines, as in (B)) and azimuth contours (dashed lines, as in (E)). (D) Continuous horizontal retinotopy map. Positive values indicate the nasal visual field and negative values the temporal visual field, with the vertical meridian located at ~60° azimuth (purple-red). (E) Contour lines of horizontal eccentricity with 20° spacing. (F) Overlay of continuous horizontal retinotopy map (as in (D)) with azimuth contours (solid lines, as in (E)) and altitude contours (dashed lines, as in (B)). (G) Overlay of vertical retinotopy contour lines (as in (B)) with area borders (black lines, as in (I)). (H) Overlay of horizontal retinotopy contour lines (as in (E)) with area borders (black lines, as in (I)). V1 borders extrastriate areas LM, AL, and RL laterally at a reversal at the vertical meridian (purple-red). LI borders LM laterally at a reversal at the temporal periphery (green-yellow). Areas AM and PM border V1 medially at a reversal at the temporal periphery (green-yellow). (I) Area border diagram of mouse visual cortex. Borders determined based on reversals at peripheries in the vertical and horizontal maps, taking into account high-resolution mapping data (Figure 2 and Figure S2), and correspondence with previous descriptions of areal organization in mouse visual cortex (Wagor et al., 1980; Wang and Burkhalter, 2007). All panels same scale; scale bars 500 μm.

Figure 2. Fine-scale retinotopic organization of mouse visual cortical areas, measured with two-photon calcium imaging

(A–L) Representative high-resolution retinotopic maps of mouse visual cortex. Area borders and names correspond to diagram in Figure 1I. Colors represent retinotopic eccentricity as described in Figure 1. Panels A, E & I show continuous vertical retinotopy maps, in altitude coordinates. Panels B, F and J show the corresponding contour plots of vertical retinotopy with area borders outlined in black. Panels C, G and K show continuous horizontal retinotopy maps, in azimuth coordinates. Panels D, H and L show contour plots of horizontal retinotopy, overlaid with area borders. (A–D) Retinotopic organization of lateral extrastriate areas and their borders with V1. Area borders shown in (B, D) correspond to V1, LM, LI, AL, and RL (starting at bottom right, moving clockwise). A reversal at the vertical meridian (nasal periphery, ~60°, purple-red in (C, D)) delineates the border between V1 and extrastriate areas LM, AL and RL. A reversal at the temporal periphery (yellow, (C, D)) marks the border between LM and LI. The border between LM and AL is identified at the reversal near the horizontal meridian (~20°, blue in (A, B)). AL is separated from RL by a representation of the vertical meridian, extending lateral and anterior from the vertical meridian in V1 (purple-blue, (C,D), see also Figure S2E–H). (E–H) Retinotopic organization of anterior and medial extrastriate areas and their borders with V1. Area borders shown in (F, H) correspond to V1, LM, AL, RL, A, AM, and PM (starting at lower left, moving clockwise). The border between V1 and PM is identified by a reversal at the temporal periphery (green-yellow, (E, F)). A representation near the vertical meridian marks the border between AM and PM (blue-purple, (G, H)). (I–L) Retinotopic organization of 7 visual areas along the nearly entire medial-lateral extent of the visual cortex. Areas shown include LM, AL, RL, A, AM, PM, and V1 (starting from lower left, moving clockwise). All scale bars 500 μm. See also Figure S2 for high resolution maps of P, POR and the ring-like structure of area RL. All scale bars 500 μm.

Figure 3. Neurons in higher visual areas are selective for particular stimulus features

(A) Example calcium imaging experiment in area AL. Left panel, example two-photon field of view. Right panels show 3 highly responsive neurons, displayed as a matrix of all stimulus conditions for a given experiment. Columns indicate the direction/orientation of the drifting grating, and rows designate the spatial frequency (SF, upper matrices) or temporal frequency (TF, lower matrices). Gray boxes illustrate the duration of the stimulus, 2 seconds for SF experiments and 4 seconds for TF experiments. The average response across all trials of a given stimulus condition is shown in black, with the responses to each trial in gray. Scale bar to lower right of each response matrix indicates 40% ΔF/F. Tuning curves were generated from response matrices by computing the average ΔF/F over the two second window following the stimulus onset for each condition along the relevant stimulus dimension. Orientation tuning curves (yellow) are taken at the optimal SF. SF (orange) and TF (magenta) tuning curves are taken at the preferred direction. Values describing selectivity metrics (OSI, DSI), the preferred spatial and temporal frequencies (pref. SF, pref. TF), as well as low cutoff (LC) and high cutoff (HC) frequencies, are listed above the corresponding tuning curves. Scale bars indicate 20% ΔF/F, and correspond to all tuning curves for a given cell. (B) Representative tuning curves from each visual area demonstrate the diversity and selectivity of receptive field properties across the populations. Horizontal axes are identical to corresponding tuning curves shown in (A), orientation/direction (yellow in (A), first column in (B)), SF (orange in (A), second column in (B)) and TF (magenta in (A), third column in (B)). Scale bars represent 20% ΔF/F and correspond to the set of tuning curves for a given cell. Rows with one scale bar show Dir, SF and TF tuning curves taken from the same neuron, as in (A). In some cases, the Dir and SF tuning curves are from one neuron, but the TF tuning curve is from a different neuron, indicated by the presence of a scale bar between the SF and TF curves. Example responses from neurons in each area are displayed in Figure S3.

Figure 4. Encoding for temporal frequency information differs across visual areas

(A) Cumulative distributions of preferred temporal frequency (TF) for each visual area (inset color-coding for each area corresponds to all panels). (B) Geometric mean preferred TF for each visual area. (C) Proportions of highpass, bandpass and lowpass neurons for each area. (D) Geometric mean TF cutoffs show the range of TFs encoded by each population on average. For each area, the left bar indicates the low cutoff TF and the right bar indicates the high cutoff frequency. Asterisks and lines above plot indicate significant differences (p < 0.05) between V1’s high cutoff frequency and the low cutoff frequency of extrastriate areas. Insets in (B) and (D) show statistical significance (p < 0.05) of pair-wise comparisons between areas, corrected for multiple comparisons using the Tukey-Kramer method. Error bars are standard error of the mean (S.E.M.) in (B, D). TF bandwidth comparisons are in Figure S4.

Figure 5. Encoding for spatial frequency information differs across visual areas

(A) Cumulative distributions of preferred spatial frequency (SF) for each visual area. (B) Geometric mean preferred SF for each area. (C) Visual areas differ in the proportions of highpass, bandpass and lowpass neurons across each population. (D) Geometric mean SF cutoffs across visual areas. For each area, left bar indicates the low cutoff SF and the right bar indicates the high cutoff SF. Insets in (B) and (D) show statistical significance (p < 0.05) of pair-wise comparisons between areas, corrected for multiple comparisons using the Tukey-Kramer method. Error bars are standard error of the mean (S.E.M.) in (B, D). SF bandwidth comparisons are in Figure S5.

Figure 6. Encoding for orientation and direction information differs across visual areas

(A) Cumulative distributions of orientation selectivity index (OSI) for each area. (B) Mean OSI for each visual area. (C) Percent of highly orientation selective neurons (OSI > 0.5) across the population for each area. (D) Cumulative distributions of direction selectivity index (DSI) for the population of neurons in each visual area. (E) Mean DSI for each visual area. (F) Percent of highly direction selective neurons (DSI > 0.5) across the population for each visual area. Insets in (B) and (E) show statistical significance (p < 0.05) of pair-wise comparisons between areas, corrected for multiple comparisons using the Tukey-Kramer method. Error bars are standard error of the mean (S.E.M.) in (B, D).

Figure 7. Mouse cortical visual areas encode unique combinations of spatiotemporal information

(A–F) Pair-wise combinations between mean preferred temporal frequency, preferred spatial frequency, OSI and DSI as a function of visual area. For all plots, each point represents the population means of a single visual area for the combination of tuning metrics indicated on the respective axes. Lines extending from each point define an area’s standard error of the mean (S.E.M.) for the tuning metric defined on the parallel axis. Statistical comparisons between areas for each metric are same as insets in Figures 4B, 5B, 6B and 6E. See cell-by-cell population correlations for each metric for each area in Figure S6.

Figure 8. Summary of feature selectivities across seven mouse visual areas

Mean values for orientation selectivity, direction selectivity, preferred spatial frequency and preferred temporal frequency for each area, corresponding to results depicted in Figures 4–7, summarized together here to illustrate the specific combinations of spatial and temporal features encoded by each area. Color intensity represents the magnitude of each parameter relative to the lowest and highest values across all areas, with higher values indicated by darker colors. Comparison of tuning for multiple stimulus parameters reveals the unique combination of spatiotemporal information represented by each area and highlights the similarities and differences across areas.