Tuning and timing of excitation and inhibition in primary auditory nerve fibers

Abstract

Information about the tuning and timing of excitation, adaptation and suppression in an auditory primary afferent axon can be obtained from the second-order Wiener kernel. Through the process of singular-value decomposition, this information can be extracted from the kernel and displayed graphically in separate two-dimensional images for excitation and inhibition 1 1 In this paper, we use the term inhibition to include all of those phenomena (such as adaptation and rate suppression) that result in reduction of instantaneous spike rate in a primary auditory afferent axon; it does not imply involvement of inhibitory synapses. We use excitation to include all of those phenomena that result in increase of instantaneous spike rate. . For low- to mid-frequency units, the images typically include checkerboard patterns. For all units they may include patterns of parallel diagonal lines. The former represent non-linearities in the phase-locked (ac) response of the unit; the latter reflect non-linear envelope-following (dc) responses. Examples of detailed interpretation are presented for three amphibian-papillar units from the American bullfrog. The second-order Wiener kernel itself is derived from second-order reverse correlation between spikes and a continuous, non-repeating, broad-band white-noise stimulus.