A Neural Code for Low-frequency Sound Localization in Mammals

We report a systematic relationship between sound-frequency tuning and sensitivity to interaural time delays for neurons in the midbrain nucleus of the inferior colliculus; neurons with relatively low best frequencies (BFs) showed response peaks at long delays, whereas neurons with relatively high BFs showed response peaks at short delays. The consequence of this relationship is that the steepest region of the function relating discharge rate to interaural time delay (ITD) fell close to midline for all neurons irrespective of BF. These data provide support for a processing of the output of coincidence detectors subserving low-frequency sound localization in which the location of a sound source is determined by the activity in two broad, hemispheric spatial channels, rather than numerous channels tuned to discrete spatial positions.