Figure 7.

LOC innervation density decreases with age, but not after correction for the loss of IHCs. A, Each point shows the mean area of the ChAT-positive boutons in the IHC area, averaged over 11 half-octave samples within the audiometric frequency range (0.25–8.0 kHz inclusive) in each case. The correlation coefficient and p value for the linear regression is shown. B, Frequency pattern of LOC area measures, showing mean values (±SEMs), for cases arbitrarily divided into three age groups, as shown by the gray boxes in A. C, Same data as in B, except the areas have been divided by the number of surviving IHCs in the same z-stacks. In all panels, LOC area is expressed in kilopixels, as extracted from maximum projections in the xy plane, such as those in Figures 3B and 2D. The ChAT immunostaining in LOC area for the youngest subject (0.1 years) was too dim and indistinct to be reliably measured. The intergroup differences are not statistically significant (n.s.): precise p values are in the text.