The guide to plotting a cochleogram

The cochleogram is commonly used for illustrating hair cell loss after insult, yet standardized procedures for plotting either individual or averaged cochleograms are lacking despite more than 40 years of use. Due to the intra-species variation in basilar membrane (BM) length, it is important that length is plotted on the cochleogram in percent and not millimeter. It is also of interest to correlate the location of lesion to frequency by using a frequency-place equation. However, there is no consensus as which equation is most suitable for the species under study. This is an important issue since two different equations can result in significantly different frequency-place maps for the same cochlea. The purpose of this presentation is to suggest procedures for standardizing the cochleogram. The guidelines include: (i) basilar membrane length should be plotted as percent instead of millimeter due to the biological variation that exists in BM length within a particular species and strain, and the total length in millimeter stated on the cochleogram; (ii) the equations used for frequency-place maps should be stated on the cochleogram; (iii) different basilar membrane lengths should be normalized to percent before averaged cochleograms are made. These procedures are illustrated and discussed.