Changes in spontaneous activity and CNS morphology associated with conductive and sensorineural hearing loss in chickens.

The effects of a conductive or mixed (conductive and sensorineural) hearing loss on anatomical and physiological properties of the chicken auditory system were examined. Animals used in the anatomical studies underwent either a columella (ossicle) removal, which produced a moderate conductive hearing loss, or an oval window puncture, which produced a severe mixed hearing loss, at 4 days posthatch. In a companion study, multiunit spike counts were obtained from 3-week-old chickens before, during, and after consecutive tympanic membrane puncture, columella removal, and oval window puncture. Tympanic membrane puncture and columella removal (conductive hearing loss) are not associated with either cell area changes in the nucleus magnocellularis or changes in spontaneous neuronal activity. Conversely, an oval window puncture (sensorineural damage) is associated with a cell area reduction of 20%, as well as a marked decline in activity within auditory nuclei.