The dorsal cochlear nucleus (DCN, also known as the "tuberculum acusticum"), is a cortex-like structure on the dorso-lateral surface of the brainstem. Along with the

ventral cochlear nucleus In the ventral cochlear nucleus (VCN), auditory nerve fibers enter the brain via the nerve root in the VCN. The ventral cochlear nucleus is divided into the anterior ventral (anteroventral) cochlear nucleus (AVCN) and the posterior ventral (poster ...

(VCN), it forms the cochlear nucleus (CN), where all auditory nerve fibers from the cochlea form their first synapses.

Anatomy

The DCN differs from the ventral portion of the CN as it not only projects to the central nucleus (a subdivision) of the

inferior colliculus The inferior colliculus (IC) (Latin for ''lower hill'') is the principal midbrain nucleus of the auditory pathway and receives input from several peripheral brainstem nuclei in the auditory pathway, as well as inputs from the auditory cortex. The ...

(CIC), but also receives efferent innervation from the auditory cortex,

superior olivary complex The superior olivary complex (SOC) or superior olive is a collection of brainstem nuclei that functions in multiple aspects of hearing and is an important component of the ascending and descending auditory pathways of the auditory system. The SO ...

and the inferior colliculus. The cytoarchitecture and

neurochemistry Neurochemistry is the study of chemicals, including neurotransmitters and other molecules such as psychopharmaceuticals and neuropeptides, that control and influence the physiology of the nervous system. This particular field within neuroscience e ...

of the DCN is similar to that of the

cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebe ...

, an important concept in theories of DCN function. Thus, the DCN is thought to be involved with more complex auditory processing, rather than merely transferring information. The

pyramidal cells Pyramidal cells, or pyramidal neurons, are a type of multipolar neuron found in areas of the brain including the cerebral cortex, the hippocampus, and the amygdala. Pyramidal neurons are the primary excitation units of the mammalian prefrontal co ...

or giant cells are a major cell grouping of the DCN. These cells are the target of two different input systems. The first system arises from the auditory nerve, and carries acoustic information. The second set of inputs is relayed through a set of small granule cells in the cochlear nucleus. There are also a great number of neighbouring cartwheel cells. The granule cells in turn are the target of a number of different inputs, including both those involved in auditory processing and, at least in lower mammals, somatosensory inputs associated with the head, the ear, and the jaw. Projections from DCN principal cells form the dorsal acoustic stria, which ultimately terminate in the CIC. This projection overlaps with that of the lateral superior olive (LSO) in a well-defined manner, where they form the primary excitatory input for ICC type O units.

Physiology

Principal cells in the DCN have very complex frequency intensity tuning curves. Classified as cochlear nucleus type IV cells, the

firing rate Rate of fire is the frequency at which a specific weapon can fire or launch its projectiles. This can be influenced by several factors, including operator training level, mechanical limitations, ammunition availability, and weapon condition. In m ...

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

, 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 their 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).

References

External links

NIF Search - Dorsal Cochlear Nucleus
via the

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{{Authority control Cranial nerve nuclei Auditory system