Physiology
Principal cells in the DCN have very complex frequency intensity tuning curves. Classified as cochlear nucleus type IV cells, the firing rate may be very rapid in response to a low intensity sound at one frequency and then fall below the spontaneous rate with only a small increment in stimulus frequency or intensity. The firing rate may then increase with another increment in intensity or frequency. Type IV cells are excited by wide band noise, and particularly excited by a noise-notch stimulus directly below the cell's best frequency (BF).
While the VCN bushy cells aid in the location of a sound stimulus on the horizontal axis via their inputs to the superior olivary complex, type IV cells may participate in localization of the sound stimulus on the vertical axis. The pinna selectively amplifies frequencies, resulting in reduced sound energy at specific frequencies in certain regions of space. The complicated firing patterns of type IV cells makes them especially suited to detecting these notches, and with the combined power of these two localization systems, an ordinary person can locate where a firework explodes without the use of his eyes.
Somatosensory inputs inhibit type IV cell activity, possibly silencing their activity during head and pinna movements. While this has not been studied extensively, it may play an important role in sound source localization in elevation. A similar effect is seen in the visual system in an effect known as change blindness.
Current auditory models of the DCN employ a two-inhibitor model. Type IV cells receive excitation directly from the auditory nerve, and are inhibited by type II (vertical) cells and a wide band inhibitor (onset-c cells).
Read more about this topic: Dorsal Cochlear Nucleus
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