Behavioral hearing thresholds and peripheral and central measures of auditory function and their relation to age (first column), BMLD_N0Sm (second column) and BMLD_N0Sπ (third column). a–c, depict behavioral hearing thresholds (young: n = 8, middle-aged: n = 9, old: n = 3), (d–f) the number of functional synapses between inner hair cells and auditory nerve fibers (young: n = 6, middle-aged: n = 9, old: n = 1), (g–i) the slopes of wave I of the auditory brainstem response (ABR) growth function (young: n = 8, middle-aged: n = 8, old: n = 1), (j–l) the amplitude of the first negative deflection (DN1) of the binaural interaction component (young: n = 5, middle-aged: n = 7, old: n = 1) and (m–o) the GABA_A receptor (GABA_AR) binding potential measured by [¹⁸F]flumazenil (FMZ) PET (GABA_PET, BPnd; young: n = 5, middle-aged: n = 7, old: n = 3). Age groups are marked (orange triangles: young, blue circles: middle-aged, pink squares: old). Values in (d–o) are adjusted for the time between actual measurement and behavioral data collection using the linear regression between the measured values and the animals’ age at the time of the actual measurement (see Methods). The coefficients of determination (R²) and the number of animals included (n) are given. In (g–l), data are marked for the type of experiment they stem from (filled symbols: ABR measurements during electrophysiological recordings in the IC, open symbols: dedicated ABR measurements) In (m–o), R² is shown for GABA_PET in the IC (open symbols). R² for GABA_PET in the AC (colored symbols) and the MGB (black symbols) were very similar.