Eighth-nerve action-potential tuning curves in cats before and after inducement of an acute noise trauma

Potentials and limitations of eighth-nerve action-potential tuning curves (APTC) in providing us with a measure of frequency selectivity are studied in cats. APTCs are measured, using a forward-masking technique. They are essentially wider than auditory-nerve fiber tuning curves. Width of APTCs is dependent upon test-tone sound pressure level (SPL) and masking criterion. This can be explained by assuming that APs are formed by discharges of fiber with different CFs. Acoustic traumata are induced halfway into the experiments in order to measure APTCs before and during the trauma in the same animal. This broad-band noise exposure resulted in a long-lasting temporary threshold shift which remained fairly steady during the experiment. In the traumatized ear APTCs are wider than in the normal ear. This widening, also observed in auditory-nerve fibers, is not simply an SPL effect.