Compound action-potential tuning curves in normal and acoustically traumatized cats.

Compound action-potential tuning curves, using a forward-masking paradigm, were developed on both a control group and a group of acoustically traumatized cats. Differences observed between the two populations included a decrease in the sharpness of the tip, in the sensitivity of the tip, and/or in the sensitivity of the tail region. Phase-contrast light microscopy was performed on all exposed ears using a celloidin-embedding technique with horizontal sectioning. Whenever an abnormality in an action-potential tuning curve was seen, histological evidence of damage to the organ of Corti in an appropriate region corresponding to the signal frequency was observed. However, several cases of damage to the cochlea were observed with normal tuning curves. Whenever the tip region of the tuning curve was elevated, evidence of damage to all three rows of outer hair cells and to the inner hair cells was seen.