Differential encoding of rapid changes in sound amplitude by second-order auditory neurons.

Single-cell recordings from the anesthetized gerbil revealed that neurons in the ventral cochlear nucleus, the most peripheral nucleus of the central auditory system, differentially encode a functionally relevant acoustic feature--amplitude modulation. Onset units show the strongest phase--locked responses to amplitude-modulated sounds, followed in order by chopper, primarylike-with-notch and primarylike units. All these neurons show enhanced responses relative to auditory-nerve fibers which provide their ascending inputs. This enhancement occurs over a 90 dB range of sound levels.