Topographic projections from MGBv, but not MGBm, to AI. A–D, Fluorescence microscopy (A, C) and retrogradely labeled cell body reconstructions (B, D) from a mouse with CTB injected into 7 and 22.6 kHz AI domains (A, B) or 5.7 and 32 kHz domains (C, D). E, F, Relative position of all retrogradely labeled cells in MGBv (E) and MGBm (F) from low (green) and high (red) injections. Data points in foreground of scatterplots reflect mean rostral-caudal and lateral-medial positions ± SEMs. G, Schematic of proposed tonotopic gradient with MGBv. Warmer colors represent higher-frequency BFs. V, MGBv; M, MGBm; D, dorsal division of MGB; CP, caudal pole; Sg, suprageniculate nucleus; R, rostral; M, medial; L, lateral. Scale bar, 0.25 mm.