Figure 3.

Visual Spatial Representations Spontaneously Emerge in the Absence of Sensory Stimulation

(A) Probability density distribution of pair-wise spontaneous neuronal activity correlations (red, Pearson linear coefficient, r) observed across experiments (n = 23). Only significant ΔF/F transients were considered. In black is the same distribution after neuronal interactivation interval shuffling (IAI) that destroys temporal coordination across neurons. 16% of neuronal pairs showed correlations that could not be explained by the latter distribution (r = 0.07 ± 0.06, p < 0.05).

(B) Example of a raster plot of spontaneous Ca²⁺ transients, revealing episodes of synchronous activations. Grayscale: ΔF/F amplitude. Bottom: histogram of the Ca²⁺ transients. The red line marks the threshold for significant population events.

(C and D) The degree of match between spontaneous network activations and the visually induced neuronal groups quantified by the matching index (MI), ranging between 0 and 1, corresponding to null and full match, respectively. (C) Top: example of MI dynamics for matches to neuronal groups induced by 4° light spots during stimulated and spontaneous activity periods (blue and red two-headed arrows, respectively). Significant MI peaks are colored according to the angular position they represent (the stimulus position that induced the activation of the neuronal group that best matched the spontaneous activation pattern; top color bar). Non-significant matches are shown in gray. For visualization purposes, we show trials with stimulation angles in increasing order. Bottom: corresponding population histogram of the neuronal Ca²⁺ transients (top, black) and the base 10 logarithm of the MI p values (bottom). MI peaks with p value < 0.01 (99% confidence; dashed gray line; see Supplemental Experimental Procedures) are considered significant and colored as in top panel. (D) Same as (C), but for direction-selective neuronal groups. Notice the absence of significant spontaneous activations.

(E) Left to right, count histograms of significant spontaneous (red) and stimulated (blue) MIs and the corresponding non-significant MI baselines (black and gray), and probability density distributions comparing these baselines and the significant MIs. Note the comparable magnitudes of spontaneous and stimulated significant MI events.

(F) Average number of significant MI events of visually evoked neuronal groups during spontaneous activities, per experiment, per neuronal group (red), for light-spot-induced (left) and direction-selective (right) neuronal groups. The number of significant events for these neuronal groups during IAI-shuffled spontaneous activities is shown in black.