SumCor peak height and width were not affected by aging. A, Example of the SumCor of a unit of a young gerbil (BF = 7.5 kHz). Inset, The SAC and XAC of the same unit (XAC/SAC ratio = 1.02). Peak height (from 0) was 1.22 (green) and peak width was 0.53 ms (magenta). B, SumCor peak height as a function of BF for young (blue circles; n = 38), middle-aged (yellow triangles; n = 19), and old gerbils (red squares; n = 28). C, SumCor peak width as a function of BF for the different age groups. Logarithmic regressions are shown as visual aids.