Neuronal frequency selectivity in the inferior colliculus and cochlear nucleus of the awake behaving macaque monkey

Frequency selectivity relates to the ability to process complex signals and can be measured through auditory filters. Behavioral filters show broader tuning compared to cochlear and auditory nerve fiber tuning. To test whether filters evolve across the auditory pathway or if they are established in the periphery, we estimated neural filters in the cochlear nucleus (CN) and inferior colliculus (IC) and compared with simultaneously measured behavioral filters in macaques. Three macaques were trained to detect tones (signal = unit characteristic frequency (CF)) in spectrally notched maskers of varying width while single unit responses were recorded in the CN and IC. Filter shapes and bandwidths were estimated from the masked thresholds using the rounded exponential fit. Behavioral and neural filters increased in bandwidth with increasing CF. Behavioral and neural bandwidths were significantly correlated and not significantly different from each other for the CN and IC. Neural filter bandwidths were variable across units and structures, possibly reflecting heterogeneity of neuronal encoding strategies. These findings support a model in which behavioral frequency selectivity is established early in the auditory pathway. These data form the baseline for ongoing studies of macaques with noise-induced hearing loss and future studies of emerging hearing loss therapeutics.