Fig. 2: Responses of Tm neurons and their presynaptic photoreceptor axons in color space.
From: Hue selectivity from recurrent circuitry in Drosophila
a–d, Relative response amplitudes of yR7 (n = 195 ROIs, 8 flies), pR7 (n = 249 ROIs, 7 flies), yR8 (n = 396 ROIs, 8 flies) and pR8 photoreceptor (n = 182 ROIs, 4 flies) axons across the gamut of tested fly colors. Top, chromatic stimuli are represented as points in the chromatic tetrahedron, with the color of each point indicating the relative response of the indicated neuron to that stimulus. The colored line that spans the edges of the tetrahedron from Rh3 to Rh4, Rh5 and Rh6 corresponds to single wavelengths ranging from 300 nm to 560 nm (that is, the visible spectrum of the fly). Bottom, stimuli are represented as points in the 2D color-opponent space, with the color of each point indicating the relative response of the indicated neuron to that stimulus. The arrows correspond to the hue sensitivity vector (Methods). The solid black line corresponds to the single wavelength line, ranging across all single wavelengths from 330 nm to 530 nm. e–h, Same as a–d for Tm5a (n = 257 ROIs, 12 flies), Tm5b (n = 354 ROIs, 13 flies), Tm5c (n = 528 ROIs, 8 flies) and Tm20 (n = 289 ROIs, 16 flies). i, Mean luminance invariance indices for photoreceptors and Tm neurons (horizontal lines). The luminance invariance index is the ratio of the goodness of fit (R2) of a linear regression using only the chromatic dimensions and the R2 of a linear regression using only the achromatic dimension. The boxes correspond to a vertical histogram of the bootstrapped distribution. j, Mean sparsity indices for photoreceptors and Tm neurons (horizontal lines). A value of 0.5 corresponds to a uniform response distribution. The boxes correspond to a vertical histogram of the bootstrapped distribution. k, Mean hue sensitivity indices for photoreceptors and Tm neurons. The index quantifies tuning sharpness in stimulus space, with values near 1 indicating the neuron responds selectively to one stimulus direction, and values near 0 indicating equivalent responses across all stimulus directions. The boxes correspond to a vertical histogram of the bootstrapped distribution.
