Coding of object location by heterogeneous neural populations with spatially dependent correlations in weakly electric fish
Fig 5
Spatial modulation of spike-count correlations depends on the level of baseline correlations.
(A) Magnitude of pairwise baseline correlations (|rBL|; black circles) as a function of the relative distance between neurons with a fitted exponential curve (black line). A threshold of |rBL| = 0.15 (red line) was used to separate neural pairs into high and low |rBL| pairs. (B) The spatial depth of modulation (max.-min.) of the spike-count correlations (|rSC|) is significantly higher for high |rBL| pairs than for low |rBL| pairs across recording sessions (Wilcoxon rank sum test for b: p = 2.1 · 10−128; outliers were removed as detailed in the Materials and Methods section). (C) Spatial dependence of the |rSC| is shown for four example pairs, two same-type pairs (OFF-OFF type pairs) and two opposite-type pairs (ON-OFF type pairs) each with low and high |rBL|. For high |rBL| pairs (left column), the spatial dependence of the |rSC| (black) is determined by the region of receptive field overlap (receptive field neuron 1 blue, receptive field neuron 2 purple): in regions where the surrounds of both neurons overlap, the |rSC| approaches |rBL| (green background); in regions where the surround of one neuron overlaps the center of the other, the |rSC| is intermediate (pink background); and in regions where there is center-center overlap, the |rSC| approaches zero (blue background). In contrast, for low |rBL| pairs of either type (right column), there is minimal or no spatial modulation and the magnitude hovers near zero. (D) Distributions of |rSC| for regions of center-center (blue), center-surround (pink) and surround-surround overlap (green) pooled over all pairs across all recording sessions: for high |rBL| pairs (left) the three distributions are significantly different (Kruskal-Wallis: p = 1.8 · 10−131; cc-cs: p = 9.7 · 10−10; cc-ss: p = 9.6 · 10−10; cs-ss: p = 9.6 · 10−10); however, they are not significantly different for low |rBL| pairs (right; Kruskal-Wallis: p = 0.89; cc-cs: p = 0.94; cc-ss: p = 0.89; cs-ss: p = 0.99). “*” indicates statistical significance; ns, not significant; c, center; s, surround.