Effects of noise induced permanent threshold shift on single units in the cochlear nucleus

Chinchillas were exposed to nonreverberant impulse noise (50 impulses, 1/min, 155 dB p.e. SPL, 1‐msec A duration) and allowed to recover for at least 40 days following the exposure. Single neurons were subsequently sampled from the dorsal and ventral cochlear nucleus. Many units from the noise exposed animals had abnormally high thresholds and broad tuning curves. Due to the shallow slope of the low‐frequency tail of the tuning curve, some units gave responses that were exclusively inhibitory. In other units, the threshold for the inhibitory area was 30–40 dB lower than the threshold for the excitation area. Many of the high‐threshold units also showed abnormally high rates of spontaneous activity. The results of single unit experiments are compared with the nature and extent of the cochlear lesions obtained using the surface preparation.