Saccade-Responsive Visual Cortical Neurons Do Not Exhibit Distinct Visual Response Properties

Abstract

Rapid saccadic eye movements are used by animals to sample different parts of the visual scene. Previous work has investigated neural correlates of these saccades in visual cortical areas such as V1; however, how saccade-responsive neurons are distributed across visual areas, cell types, and cortical layers has remained unknown. Through analyzing 818 1 h experimental sessions from the Allen Brain Observatory, we present a large-scale analysis of saccadic behaviors in head-fixed mice and their neural correlates. We find that saccade-responsive neurons are present across visual cortex, but their distribution varies considerably by transgenically defined cell type, cortical area, and cortical layer. We also find that saccade-responsive neurons do not exhibit distinct visual response properties from the broader neural population, suggesting that the saccadic responses of these neurons are likely not predominantly visually driven. These results provide insight into the roles played by different cell types within a broader, distributed network of sensory and motor interactions.

Keywords: calcium imaging; mouse visual cortex; saccades; transgenic lines.

Figure 1.

Saccade behavior is not influenced by visual stimulus. A, Left, Example frame from eye video annotated with axes of eye movement (x-axis, nasal–temporal; y-axis, dorsal–ventral). Middle, Example ellipse fits on eyeball (green), pupil (blue), and glare spot (red) from DeepLabCut model (Materials and Methods). Right, Example azimuth (horizontal) and elevation (vertical) traces from an experiment session after pupil extraction (Materials and Methods). Top trace is the elevation (y-degree, vertical), bottom trace is the azimuth (x-degree, horizontal), and dashed line indicates 0°. Upward is positive, and downward is negative using the same signs as in the left subplot. Times of abrupt eye position change correspond to saccades. B, Intersaccade intervals (s), defined as the time elapsed before the preceding saccade, for all saccades. Of n = 202,156 total saccades, 33.5% saccades occurred at most 2 s after a previous saccade. C, Top, Example saccade motions from one experiment session, where each saccade has been aligned to start at the origin. Each saccade is a separate line, and points on the line indicate eye position at frames during the saccade. Note that saccades are made preferentially in the horizontal direction. Bottom, Direction classification of saccades. Each sector of the circle is 90°; dashed black line indicates the horizontal axis. Middle intersection point denotes eye position alignment of the start of saccade. T, Temporal; D, dorsal; N, nasal; V, ventral. D, Example nasal and temporal saccades from one experiment session. Dashed line represents 0°, and traces are centered by subtracting the position at the time of saccade onset. Only azimuthal (horizontal) traces are shown. E, Distributions of saccade magnitude for nasal and temporal saccades. Nasal saccades (n = 104,121), 7.10 ± 3.19° (mean ± SD); temporal saccades (n = 91,037), 6.14 ± 2.78°. Grouped together, all horizontal saccades (n = 195,158) had magnitude 6.65 ± 3.05°. Density normalization accounts only for saccades in the given direction (i.e., y-axis is normalized so both nasal and temporal area curves have unit area). F, Ratio of mean temporal saccade magnitude to mean nasal saccade magnitude in each individual session. Dashed vertical line at 1, indicating an equal magnitude of nasal and temporal saccades. G, Left, Visual stimuli abbreviations used in this figure and throughout the article. Middle, Saccade frequency for different visual stimuli. Each data point is the average saccade frequency of a mouse for a particular visual stimulus (Materials and Methods). Box line corresponds to the 25th to 75th percentile, line corresponds to median (50%), and error bars at 10% and 90%. Right, Probability heatmap matrix comparing mouse mean saccade frequencies across different stimulus types using a two-sample KS test. Heatmap is centered at Bonferroni-corrected significance value (p = 0.05/8 ≅ 6e-3).

Figure 2.

Diverse responses of neurons in visual cortex to saccades. A, Example neuron with a significant activity modulation (Materials and Methods; p = 0.0024, Wilcoxon signed-rank test). Neuron 669928467 (Tlx3;Ai148, VISl, L5, session 658854486). Left, Each row is a dF/F trace centered around a saccade, where saccades are ordered in chronological order (top corresponds to the start of the experiment) and time 0 corresponds to the start of each saccade. Second from left, All temporal and nasal saccades (indicated by red and blue bars), where each group is sorted by magnitude (largest magnitude on top). Third from left, Mean dF/F of neuron around saccades. Nasal (blue) and temporal (red) traces are mean dF/F around nasal and temporal saccades, respectively; all (black) corresponds to dF/F average around all saccades. Baseline is a N = 1000 bootstrapped distribution where each trace is the mean of random time points within the experiment session (the number of random samples equals the number of saccades). Right, dF/F average around preferred saccades by stimulus type. Baseline is the distribution from the previous subplot; the number in the legend is the number of preferred saccades during each stimulus. B, Example SR neuron with an enhanced response to saccades, regardless of direction. Neuron 517476630 (Cux2;Ai93, VISal L2/3, session 506156402). C, Example SR neuron with a suppressed response to saccades, regardless of direction. Neuron 670074250 (Cux2;Ai93 VISrl L2/3, session 662960692). D, Example SR, DS neuron preferring nasal saccades. Neuron 662076627 (Ntsr1;Ai148, VISp L6, session 606227591). E, Example SR, DS neuron preferring temporal saccades. Neuron 662209107 (Ntsr1;Ai148, VISp L6, session 636889229). F, Scatter plot of saccade-responsive enhanced neurons showing their mean temporal saccade response (x-axis) and mean nasal saccade response (y-axis). Blue dot indicates that a neuron prefers nasal saccades; red dot indicates that neuron prefers temporal saccades; black “x” indicates the neuron is not direction selective. Mean nasal/temporal response for nasal neurons, 0.0528/0.0074; temporal neurons, 0.0015/0.0490; non-direction-selective neurons, 0.0249/0.0302. See Extended Data Figure 5-1A for distribution where SR neurons are detected using saccades during spontaneous visual stimulus. G, Direction selectivity index histogram for saccade-responsive enhanced neurons. Gray, All saccade-responsive enhanced neurons (n = 2696); blue, neurons that prefer nasal saccades (n = 318); red, neurons that prefer temporal saccades (n = 1467). Bar is the middle 50% (all: −0.01, 0.93; nasal: −1.02, −0.39; temporal: 0.58, 1.27); dot is the median (all, 0.49; nasal, −0.68; temporal, 0.84). See Extended Data Figure 5-1A for distributions where SR neurons are detected using saccades during spontaneous visual stimulus.

Figure 3.

Saccade responses are more strongly suppressed by naturalistic stimuli. A, Comparison of mean response to saccades made during spontaneous visual stimulus and other visual stimuli (Materials and Methods). Significance value is p = 0.05 using Wilcoxon rank-sum test. B, Ratio of the mean response to preferred saccades made during NM-1 to the mean response of preferred saccades made during spontaneous for each saccade-responsive neuron. Vertical black dashed line at 1 indicates equal response. Green dot is the median ratio, bars extend to 25% and 75%. See Extended Data Figure 3-1 for an analogous plot for each visual stimulus.

Figure 4.

Differences in saccade responses across transgenic lines and visual areas. A, Heatmap of the percentage of SR neurons by transgenic line and visual area, relative to the total number of imaged neurons, which is given above each bar. B, Left, Percentage of SR neurons by transgenic line, broken down by type of response. “Enhanced: No DS” means that the neuron has an enhanced response to saccades but does not prefer any one direction (Materials and Methods). Number above each bar is the total number of imaged neurons of the corresponding line. Low-opacity bars indicate inhibitory neurons. Right, χ² test across pairings of transgenic lines (using a 2 × 2 contingency matrix containing number of SR and non-SR neurons for each line). C, Left, Percentage of SR neurons by visual area. Number above each bar is the total number of imaged neurons in the corresponding area. Right, Heatmap; same as in B. D, Percentage of SR neurons by cortical layer and visual area. Hatched marks indicate neurons with a suppressed saccade response. E, Percentage of SR neurons by transgenic line and cortical layer, across all visual areas. Low-opacity bars indicate inhibitory neurons, and the numbers above bars indicate the total number of neurons imaged. See Extended Data Figure 4-1 for an analogous plot for neurons only in V1.

Figure 5.

Saccade-responsive neurons have similar visual responses to non-saccade-responsive neurons. A, Left, Percentage of SR neurons by visual response class, indicating which set of visual stimuli elicit a response. Number above each bar is the total number of imaged neurons within the given cluster. Right, χ² test across pairings of transgenic lines (contingency matrix containing number of SR and non-SR neurons for each cluster; p = 0.05, Bonferroni corrected for multiple comparisons). B, Orientation selectivity index for neurons that respond to drifting gratings. Curve is smoothed using a Gaussian kernel. Inset, Heatmap shows a KS test between different distributions (p = 0.05, Bonferroni corrected for multiple comparisons). C, Analogous plot to B, showing lifetime sparseness for neurons responsive to natural scenes. D, Analogous plot to B, showing a direction selectivity index plot for neurons responsive to drifting gratings. E, Distribution of preferred direction for neurons responsive to drifting gratings. See Extended Figure 5-1 for an analogous figure where SR neurons are detected using saccades during the spontaneous visual stimulus (Methods).