Editing Auditory system (section)

== Neuronal structure ==

=== Cochlear nucleus ===
{{main|Cochlear nucleus}}

The [[cochlear nucleus]] is the first site of the neuronal processing of the newly converted "digital" data from the inner ear (see also [[binaural fusion]]).  In mammals, this region is anatomically and physiologically split into two regions, the [[dorsal cochlear nucleus]] (DCN), and [[ventral cochlear nucleus]] (VCN).  The VCN is further divided by the nerve root into the posteroventral cochlear nucleus (PVCN) and the anteroventral cochlear nucleus (AVCN).<ref>{{Cite book |title=Encyclopedia of Neuroscience |vauthors=Middlebrooks JC |publisher=Academic Press |year=2009 |isbn=978-0-08-044617-2 |veditors=Squire LF |pages=745–752, here: p. 745 f |chapter=Auditory System: Central Pathways}}</ref>

=== Trapezoid body ===
{{main|Trapezoid body}}

The [[trapezoid body]] is a bundle of [[decussation|decussating]] fibers in the ventral pons that carry information used for binaural computations in the brainstem. Some of these [[axon]]s come from the [[cochlear nucleus]] and [[decussation|cross over]] to the other side before traveling on to the [[superior olivary complex|superior olivary nucleus.]]  This is believed to help with [[sound localization|localization of sound]].<ref>{{Cite book |title=Encyclopedia of Clinical Neuropsychology |vauthors=Mendoza JE |date=2011 |publisher=Springer |isbn=978-0-387-79947-6 |veditors=Kreutzer JS, DeLuca J, Caplan B |location=New York |pages=2549 |chapter=Trapezoid Body |doi=10.1007/978-0-387-79948-3_807}}</ref>

=== Superior olivary complex ===
{{main|Superior olivary complex}}

The [[superior olivary complex]] is located in the [[pons]], and receives projections predominantly from the ventral cochlear nucleus, although the dorsal cochlear nucleus projects there as well, via the ventral acoustic stria.  Within the [[superior olivary complex]] lies the lateral superior olive (LSO) and the medial superior olive (MSO).  The former is important in detecting interaural level differences while the latter is important in distinguishing [[interaural time difference]].<ref name="pmid11071722"/>

[[File:Lateral lemniscus.PNG|thumb|right|200px| '''Lateral lemniscus''' in red, as it connects the [[cochlear nucleus]], [[superior olivary nucleus]] and the [[inferior colliculus]], seen from behind]]

=== Lateral lemniscus ===
{{main|Lateral lemniscus}}

The lateral lemniscus is a tract of [[axon]]s in the [[brainstem]] that carries information about sound from the [[cochlear nucleus]] to various brainstem nuclei and ultimately the contralateral [[inferior colliculus]] of the [[midbrain]].

=== Inferior colliculi ===
{{main|Inferior colliculus}}

The inferior colliculi (IC) are located just below the visual processing centers known as the [[superior colliculus|superior colliculi]].  The central nucleus of the IC is a nearly obligatory relay in the ascending auditory system, and most likely acts to integrate information (specifically regarding sound source localization from the [[superior olivary complex]]<ref name="pmid11071719"/> and [[dorsal cochlear nucleus]]) before sending it to the [[thalamus]] and [[Cerebral cortex|cortex]].<ref name="pmid14714940">{{Cite journal |vauthors=Demanez JP, Demanez L |year=2003 |title=Anatomophysiology of the central auditory nervous system: basic concepts |journal=Acta Oto-Rhino-Laryngologica Belgica |volume=57 |issue=4 |pages=227–36 |pmid=14714940}}</ref>  The inferior colliculus also receives descending inputs from the [[auditory cortex]] and auditory [[thalamus]] (or [[medial geniculate nucleus]]).<ref>{{Cite book |last=Schreiner |first=Christoph |title=The Inferior Colliculus |url=https://link.springer.com/book/10.1007/b138578 |date=2005 |publisher=Springer Science+ Business Media, Incorporated |isbn=0-387-22038-0 |editor-last=Winer |editor-first=Jeffery A |doi=10.1007/b138578 |editor-last2=Schreiner |editor-first2=Christoph E |access-date=2022-05-17 |archive-date=2022-05-17 |archive-url=https://web.archive.org/web/20220517133305/https://link.springer.com/book/10.1007/b138578 |url-status=live }}</ref>

=== Medial geniculate nucleus ===
{{main|Medial geniculate nucleus}}

The [[medial geniculate nucleus]] is part of the thalamic relay system.

=== Primary auditory cortex ===
{{main|Primary auditory cortex}}

The [[primary auditory cortex]] is the first region of [[cerebral cortex]] to receive auditory input.

Perception of sound is associated with the left posterior [[superior temporal gyrus]] (STG). The superior temporal gyrus contains several important structures of the brain, including [[Brodmann areas]] 41 and 42, marking the location of the [[primary auditory cortex]], the cortical region responsible for the sensation of basic characteristics of sound such as pitch and rhythm. We know from research in nonhuman primates that the primary auditory cortex can probably be divided further into functionally differentiable subregions.<ref name="pmid8578069">{{Cite journal |vauthors=Pandya DN |year=1995 |title=Anatomy of the auditory cortex |journal=Revue Neurologique |volume=151 |issue=8–9 |pages=486–94 |pmid=8578069}}</ref><ref name="pmid9575378">{{Cite journal |vauthors=Kaas JH, Hackett TA |year=1998 |title=Subdivisions of auditory cortex and levels of processing in primates |journal=Audiology & Neuro-Otology |volume=3 |issue=2–3 |pages=73–85 |doi=10.1159/000013783 |pmid=9575378 |s2cid=46858666}}</ref><ref name="pmid10322185">{{Cite journal |vauthors=Kaas JH, Hackett TA, Tramo MJ |date=April 1999 |title=Auditory processing in primate cerebral cortex |journal=Current Opinion in Neurobiology |volume=9 |issue=2 |pages=164–70 |doi=10.1016/S0959-4388(99)80022-1 |pmid=10322185 |s2cid=22984374}}</ref><ref name="pmid11050211">{{Cite journal |vauthors=Kaas JH, Hackett TA |date=October 2000 |title=Subdivisions of auditory cortex and processing streams in primates |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=97 |issue=22 |pages=11793–9 |bibcode=2000PNAS...9711793K |doi=10.1073/pnas.97.22.11793 |pmc=34351 |pmid=11050211 |doi-access=free}}</ref>
<ref name="pmid11745645">{{Cite journal |vauthors=Hackett TA, Preuss TM, Kaas JH |date=December 2001 |title=Architectonic identification of the core region in auditory cortex of macaques, chimpanzees, and humans |journal=The Journal of Comparative Neurology |volume=441 |issue=3 |pages=197–222 |doi=10.1002/cne.1407 |pmid=11745645 |s2cid=21776552}}</ref><ref name="pmid12536133">{{Cite journal |vauthors=Scott SK, Johnsrude IS |date=February 2003 |title=The neuroanatomical and functional organization of speech perception |journal=Trends in Neurosciences |volume=26 |issue=2 |pages=100–7 |citeseerx=10.1.1.323.8534 |doi=10.1016/S0166-2236(02)00037-1 |pmid=12536133 |s2cid=10390565}}</ref><ref name="pmid11303104">{{Cite journal |vauthors=Tian B, Reser D, Durham A, Kustov A, Rauschecker JP |date=April 2001 |title=Functional specialization in rhesus monkey auditory cortex |journal=Science |volume=292 |issue=5515 |pages=290–3 |bibcode=2001Sci...292..290T |doi=10.1126/science.1058911 |pmid=11303104 |s2cid=32846215}}</ref>
The neurons of the primary auditory cortex can be considered to have [[receptive field]]s covering a range of [[audio frequency|auditory frequencies]] and have selective responses to harmonic pitches.<ref name="pmid24381544">{{Cite journal |vauthors=Wang X |date=December 2013 |title=The harmonic organization of auditory cortex |journal=Frontiers in Systems Neuroscience |volume=7 |pages=114 |doi=10.3389/fnsys.2013.00114 |pmc=3865599 |pmid=24381544 |doi-access=free}}</ref> Neurons integrating information from the two ears have receptive fields covering a particular region of auditory space.

The primary auditory cortex is surrounded by secondary auditory cortex, and interconnects with it. These secondary areas interconnect with further processing areas in the [[superior temporal gyrus]], in the dorsal bank of the [[superior temporal sulcus]], and in the [[frontal lobe]]. In humans, connections of these regions with the [[middle temporal gyrus]] are probably important for [[speech perception]].  The frontotemporal system underlying auditory perception allows us to distinguish sounds as speech, music, or noise.

=== The auditory ventral and dorsal streams ===
{{main|Language processing in the brain}}
{{Further|Two-streams hypothesis#Two auditory systems}}
[[File:Neurolinguistics.png|thumb|350px|'''Dual stream connectivity between the auditory cortex and frontal lobe of monkeys and humans.''' Top: The auditory cortex of the monkey (left) and human (right) is schematically depicted on the supratemporal plane and observed from above (with the parieto- frontal operculi removed). Bottom: The brain of the monkey (left) and human (right) is schematically depicted and displayed from the side. Orange frames mark the region of the auditory cortex, which is displayed in the top sub-figures. Top and Bottom: Blue colors mark regions affiliated with the ADS, and red colors mark regions affiliated with the AVS (dark red and blue regions mark the primary auditory fields). Abbreviations: AMYG-amygdala, HG-Heschl's gyrus, FEF-frontal eye field, IFG-inferior frontal gyrus, INS-insula, IPS-intra parietal sulcus, MTG-middle temporal gyrus, PC-pitch center, PMd-dorsal premotor cortex, PP-planum polare, PT-planum temporale, TP-temporal pole, Spt-sylvian parietal-temporal, pSTG/mSTG/aSTG-posterior/middle/anterior superior temporal gyrus, CL/ ML/AL/RTL-caudo-/middle-/antero-/rostrotemporal-lateral belt area, CPB/RPB-caudal/rostral parabelt fields. Used with permission from Poliva O. From where to what: a neuroanatomically based evolutionary model of the emergence of speech in humans. [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].
]]
From the primary auditory cortex emerge two separate pathways: the auditory ventral stream and auditory dorsal stream.<ref>{{Cite journal |vauthors=Hickok G, Poeppel D |date=May 2007 |title=The cortical organization of speech processing |journal=Nature Reviews. Neuroscience |volume=8 |issue=5 |pages=393–402 |doi=10.1038/nrn2113 |pmid=17431404 |s2cid=6199399}}</ref> The auditory ventral stream includes the anterior superior temporal gyrus, anterior superior temporal sulcus, middle temporal gyrus and temporal pole. Neurons in these areas are responsible for sound recognition, and extraction of meaning from sentences. The auditory dorsal stream includes the posterior superior temporal gyrus and sulcus, [[inferior parietal lobule]] and intra-parietal sulcus. Both pathways project in humans to the inferior frontal gyrus. The most established role of the auditory dorsal stream in primates is sound localization. In humans, the auditory dorsal stream in the left hemisphere is also responsible for speech repetition and articulation, phonological long-term encoding of word names, and verbal working memory.