This chapter deals with the coding of information in the auditory nerve. This is usually measured by monitoring the electrical responses of individual neurons or the compound output of the nerve "as a whole" during the presentation of various stimuli. Nerve fibers elicit all-or-none electrical discharges called action potentials, which are picked up by electrodes and typically appear on recording devices as "spikes" at certain points in time. The firing patterns of fibers can suggest how information is coded and transmitted in the auditory nervous system. Kiang found that the discharges of auditory nerve fibers are time-locked to tonal stimuli up to 4000 to 5000 Hz. This relationship was demonstrated by the presence on the Post-stimulus time (PST) histogram of single peaks corresponding to individual cycles of the stimulus; and it is consistent with other evidence that auditory nerve fibers respond to the particular phase of the stimulus within this frequency range.