Figures and data
Spontaneous activity in RL sparsifies over development, with more mature activity in S1 compared to V1 and RL. A. Schematic of the two-photon experiments. Primary visual cortex (V1), somatosensory cortex (S1), and rostro-lateral area (RL) imaged in sequence over a 100 min recording session. B. Sample field of views of the individual cortices. Scale bar corresponds to 50 µm. C. Sample z-profile traces from the three different cortices (columns) in three mice at different postnatal ages (rows). Vertical scale bar corresponds to 20% ΔF/F0. Horizontal scale bar corresponds to 50 seconds. D-G. Amplitude (D), duration (E), participation rate (F), and event rate (G) as a function of postnatal age. Individual dots represent averages across all events in an area from one animal. Regression lines derived from a linear mixed model in H. H. Effect sizes of age and cortical region, and interaction effects of age within cortical region (i.e. Age:S1 and Age:RL) as determined by linear mixed model analysis, where age and region are included as fixed effects, and mouse ID and sample ID are included as random effects. All comparisons are relative to V1 at PN8. Values shown for V1 are estimates of the intercept at day PN8. Values shown for Age in V1 are estimates of the slope in the linear mixed model. All interaction effects of age within region (Age:S1 and Age:RL) apply to differences in the slope for that region compared to the slope of age within V1, whereas cortical region (S1 and RL) effects apply to differences in the intercept compared to V1 at PN8 (see Methods). Stars indicate statistical significance (* p<0.05, ** p<0.01, *** p<0.001). N=10 animals.
Spontaneous activity in S1 and V1 is synchronized. A. Schematic of wide-field experiments. An area encompassing the visual (V1) and the somatosensory (S1) cortices imaged over a 100 min recording session, broken up into 5 min recordings. B. Top: Three examples of spontaneous events, predominantly in V1 (left), S1 (right), or in both primary cortices (middle). Bottom: Sample ΔF/F0 traces averaged over V1 (red) or S1 (blue). Lines indicate the time points at which the events in the top row occurred. Horizontal scale bar indicates 20 seconds. Vertical scale bar represents 50% ΔF/F0. C. Temporal correlations between V1 and S1. Violin plots where each dot indicates Pearson correlation coefficients during 2-minute bin. PN9 N=6; PN10 N=5; PN11 N=4; PN12 N=2. D,E. Spatial correlations in V1/RL and S1/RL. Functional correlation maps show that spontaneous activity in RL is coordinated topographically with activity in both V1 (D) and S1 (E). Each color represents the correlations between the fluorescent changes over time of one of three seed areas in each image (white squares) and all pixels in the field of view (for details see Methods). Higher-order areas of the visual cortex are drawn according to [11]. LM: lateromedial area, AL: anterolateral area, A: anterior area.
Model set-up and assumptions. A. Schematic of a three-population feedforward model of the developing V1, S1, and RL. B. Example of random initial connectivity matrix between V1 and RL (connectivity matrix for S1 and RL is chosen identically) with a topographic bias denoted by stronger connections along the diagonal inspired by activity-independent mechanisms (see Methods). C. Sample of spontaneous events in V1 (top) and S1 (bottom) across cells as a function of time. Boxes highlight two spatiotemporally correlated events in V1 and S1 (see Methods). D. Example of refinement of connectivity matrix between V1 and RL (top) and S1 and RL (bottom), from t0 to tN. Same axes as in Figure 2B. E. Example of connectivity matrices in steady state from simulations with low (left) to highly (right) temporally correlated activity between V1 and S1. F. Schematic to illustrate topography and alignment measures (see Methods). G-I. Topography (G), alignment (H), and percentage of bimodal cells (I) as a function of V1 to S1 correlation. Red dots correspond to the examples from E. K. Excerpt of activity in RL at the beginning (left) and end (right) of the simulation (corresponds to panel D, left and right).
More mature spontaneous events in S1 effectively instruct map alignment between V1 and RL. A. Three pairs of connectivity matrices (V1 left, S1 right) with increasing (top to bottom) S1 bias. B. Corresponding connectivity matrices in steady-state after plasticity. C. S1 and V1 topography for different S1-RL connectivity biases (indicated by color).
A mixture of bimodal and unimodal neurons can optimally decode activity. A. Schematic of regression procedure to calculate R2 for reconstructing V1 or S1 activity from RL activity with a non-linear transfer function (a sigmoid) (see Methods). A linear regression is performed using the non-linearly transformed RL activity (dependent variable) and both V1 and S1 activity (independent variables). R2 is calculated from V1 or S1 activity separately using the fitted regression line. B. Reconstruction of V1 or S1 activity (R2) as a function of the percentage of connected cells from the respective cortex over all values of correlation chosen uniformly between 0 and 1 (see Methods). Color indicates topography. C. Reconstruction of V1 and S1 activity (R2) as a function of the percentage of bimodal cells (denoted by color).
