Editing Auditory cortex (section)

== Function ==
As with other primary sensory cortical areas, auditory sensations reach [[perception]] only if received and processed by a [[cerebral cortex|cortical]] area. Evidence for this comes from [[lesion]] studies in human patients who have sustained damage to cortical areas through [[tumor]]s or [[stroke]]s,<ref>{{cite journal|last=Cavinato|first=M.|author2=Rigon, J.|author3=Volpato, C.|author4=Semenza, C.|author5=Piccione, F.|title=Preservation of Auditory P300-Like Potentials in Cortical Deafness|journal=PLOS ONE|date=January 2012|volume=7|issue=1|doi=10.1371/journal.pone.0029909|pmid=22272260|pmc=3260175|pages=e29909|bibcode=2012PLoSO...729909C|doi-access=free}}</ref> or from animal experiments in which cortical areas were deactivated by surgical lesions or other methods.<ref>{{cite journal|last=Heffner |first=H.E. |author2=Heffner, R.S. |title=Hearing loss in Japanese macaques following bilateral auditory cortex lesions |journal=Journal of Neurophysiology |date=February 1986 |volume=55 |issue=2 |pages=256–271 |pmid=3950690 |url=http://psychology.utoledo.edu/images/users/74/Lesion%20studies/Hearing_Loss_in_J_macaques_following_bilateral_AC_JN1986.pdf |access-date=11 September 2012 |archive-url=https://web.archive.org/web/20100802160254/http://psychology.utoledo.edu/images/users/74/Lesion%20studies/Hearing_Loss_in_J_macaques_following_bilateral_AC_JN1986.pdf |archive-date=2 August 2010 |doi=10.1152/jn.1986.55.2.256 }}</ref> Damage to the auditory cortex in humans leads to a loss of any [[awareness]] of sound, but an ability to react reflexively to sounds remains as there is a great deal of subcortical processing in the [[Auditory pathway#Central auditory system|auditory brainstem]] and [[midbrain]].<ref>{{cite book|last=Rebuschat|first=P. |author2=Martin Rohrmeier, M. |author3=Hawkins, J.A. |author4=Cross, I. |title=Human subcortical auditory function provides a new conceptual framework for considering modularity|journal=Language and Music as Cognitive Systems|year=2011|issue=28|doi=10.1093/acprof:oso/9780199553426.003.0028|pages=269–282|isbn=978-0-19-955342-6 }}</ref><ref>{{cite journal|last=Krizman|first=J.|author2=Skoe, E.|author3=Kraus, N.|title=Stimulus Rate and Subcortical Auditory Processing of Speech|journal=Audiology and Neurotology|date=March 2010|volume=15|pages=332–342|doi=10.1159/000289572|pmid=20215743|pmc=2919427|url=http://www.soc.northwestern.edu/brainvolts/documents/Krizman_Skoe_Kraus_AudNeuro_2010.pdf|access-date=11 September 2012|issue=5|archive-url=https://web.archive.org/web/20120415130027/http://www.soc.northwestern.edu/brainvolts/documents/Krizman_Skoe_Kraus_AudNeuro_2010.pdf|archive-date=15 April 2012}}</ref><ref>{{cite journal|last=Strait |first=D.L. |author2=Kraus, N. |author3=Skoe, E. |author4=Ashley, R. |title=Musical Experience Promotes Subcortical Efficiency in Processing Emotional Vocal Sounds |journal=Annals of the New York Academy of Sciences |year=2009 |volume=1169 |pages=209–213 |doi=10.1111/j.1749-6632.2009.04864.x |pmid=19673783 |url=http://www.soc.northwestern.edu/brainvolts/documents/strait_nyannals.pdf |access-date=11 September 2012 |issue=1 |archive-url=https://web.archive.org/web/20120415125830/http://www.soc.northwestern.edu/brainvolts/documents/Strait_NYAnnals.pdf |archive-date=15 April 2012 |bibcode=2009NYASA1169..209S |s2cid=4845922 }}</ref>

Neurons in the auditory cortex are organized according to the frequency of sound to which they respond best. [[Neuron]]s at one end of the auditory cortex respond best to low frequencies; neurons at the other respond best to high frequencies. There are multiple auditory areas (much like the multiple areas in the [[visual cortex]]), which can be distinguished anatomically and on the basis that they contain a complete "frequency map." The purpose of this frequency map (known as a [[tonotopy|tonotopic map]]) likely reflects the fact that the [[cochlea]] is arranged according to sound frequency. The auditory cortex is involved in tasks such as identifying and segregating "'''auditory'''  '''objects'''" and identifying the location of a sound in space. For example, it has been shown that A1 encodes complex and abstract aspects of auditory stimuli without encoding their "raw" aspects like frequency content, presence of a distinct sound or its echoes.<ref>{{Cite journal|last1=Chechik|first1=Gal|last2=Nelken|first2=Israel|date=2012-11-13|title=Auditory abstraction from spectro-temporal features to coding auditory entities |journal=Proceedings of the National Academy of Sciences of the United States of America|volume=109|issue=46|pages=18968–18973|doi=10.1073/pnas.1111242109|issn=0027-8424|pmc=3503225|pmid=23112145|bibcode=2012PNAS..10918968C|doi-access=free}}</ref>

Human [[brain scan]]s indicated that a peripheral part of this brain region is active when trying to identify [[musical pitch]]. Individual cells consistently get [[Membrane potential|excited]] by sounds at specific frequencies, or [[Harmonics|multiple]]s of that [[frequency]].

The auditory cortex plays an important yet ambiguous role in hearing. When the auditory information passes into the cortex, the specifics of what exactly takes place are unclear. There is a large degree of individual variation in the auditory cortex, as noted by English biologist [[James Beament]], who wrote, "The cortex is so complex that the most we may ever hope for is to understand it in principle, since the evidence we already have suggests that no two cortices work in precisely the same way."<ref>{{Cite book|last=Beament|first=James|title=How We Hear Music: the Relationship Between Music and the Hearing Mechanism|url=https://archive.org/details/howwehearmusicre0000beam|url-access=limited|place=Woodbridge|publisher=Boydell Press|year=2001|page=[https://archive.org/details/howwehearmusicre0000beam/page/93 93] |jstor=10.7722/j.ctt1f89rq1|isbn=978-0-85115-813-6}}</ref>

In the hearing process, multiple sounds are transduced simultaneously. The role of the auditory system is to decide which components form the sound link. Many have surmised that this linkage is based on the location of sounds. However, there are numerous distortions of sound when reflected off different media, which makes this thinking unlikely.{{citation needed|date=May 2014}} The auditory cortex forms groupings based on fundamentals; in music, for example, this would include [[harmony]], [[timing (music)|timing]], and [[pitch (music)|pitch]].<ref>{{Cite news|last=Deutsch|first=Diana|title=Hearing Music in Ensembles|newspaper=Physics Today|page=40|date=February 2010 |volume=63 |issue=2 |doi=10.1063/1.3326988}}</ref>

The primary auditory cortex lies in the [[superior temporal gyrus]] of the temporal lobe and extends into the [[lateral sulcus]] and the [[transverse temporal gyri]] (also called ''Heschl's gyri''). Final sound processing is then performed by the [[parietal lobe|parietal]] and [[Frontal lobe|frontal]] lobes of the human [[cerebral cortex]]. Animal studies indicate that auditory fields of the cerebral cortex receive ascending input from the [[Medial geniculate nucleus|auditory thalamus]] and that they are interconnected on the same and on the opposite [[cerebral hemisphere]]s.

The auditory cortex is composed of fields that differ from each other in both structure and function.<ref>{{cite journal|last1=Cant|first1=NB|title=Parallel auditory pathways: projection patterns of the different neuronal populations in the dorsal and ventral cochlear nuclei|journal=Brain Res Bull|volume=60|issue=5–6|pages=457–74|date=June 15, 2003|doi=10.1016/S0361-9230(03)00050-9|pmid=12787867|last2=Benson|first2=CG|s2cid=42563918}}</ref> The number of fields varies in different species, from as few as 2 in [[rodent]]s to as many as 15 in the [[rhesus monkey]]. The number, location, and organization of fields in the human auditory cortex are not known at this time. What is known about the human auditory cortex comes from a base of knowledge gained from studies in [[mammal]]s, including primates, used to interpret [[EEG|electrophysiological]] tests and [[functional imaging]] studies of the brain in humans.

When each instrument of a [[symphony orchestra]] or [[jazz band]] plays the same note, the quality of each sound is different, but the musician perceives each note as having the same pitch. The neurons of the auditory cortex of the brain are able to respond to pitch. Studies in the marmoset monkey have shown that pitch-selective neurons are located in a cortical region near the [[Anatomical terms of location#Combined terms|anterolateral]] border of the primary auditory cortex. This location of a pitch-selective area has also been identified in recent functional imaging studies in humans.<ref>{{cite journal|last=Bendor|first=D|author2=Wang, X|title=The neuronal representation of pitch in primate auditory cortex|journal=Nature|volume=436|issue=7054|pages=1161–5|year=2005|doi=10.1038/nature03867|pmid=16121182|pmc=1780171|bibcode=2005Natur.436.1161B}}</ref><ref>{{cite journal|last=Zatorre|first=RJ|title=Neuroscience: finding the missing fundamental|journal=Nature|volume=436|issue=7054|pages=1093–4|year=2005|doi=10.1038/4361093a|pmid=16121160 |bibcode=2005Natur.436.1093Z|s2cid=4429583}}</ref>

The primary auditory cortex is subject to [[Neuromodulation|modulation]] by numerous [[neurotransmitter]]s, including [[norepinephrine]], which has been shown to decrease [[Membrane potential|cellular excitability]] in all layers of the [[temporal cortex]]. [[alpha-1 adrenergic receptor]] activation, by norepinephrine, decreases [[Glutamic acid|glutamatergic]] [[excitatory postsynaptic potential]]s at [[AMPA receptor]]s.<ref name=Dinh2009>{{cite journal|last1=Dinh|first1=L|author2=Nguyen T|author3=Salgado H|author4=Atzori M|title=Norepinephrine homogeneously inhibits alpha-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate- (AMPAR-) mediated currents in all layers of the temporal cortex of the rat|journal=Neurochem Res|volume=34|issue=11|pages=1896–906|year=2009|pmid=19357950|doi=10.1007/s11064-009-9966-z|s2cid=25255160}}</ref>

=== Relationship to the auditory system ===
The auditory cortex is the most highly organized processing unit of sound in the brain. This cortex area is the neural crux of hearing, and&mdash;in humans&mdash;language and music. The auditory cortex is divided into three separate parts: the primary, secondary, and tertiary auditory cortex. These structures are formed concentrically around one another, with the primary cortex in the middle and the tertiary cortex on the outside.

The primary auditory cortex is [[wikt:tonotopically|tonotopically]] organized, which means that neighboring cells in the cortex respond to neighboring frequencies.<ref>{{cite journal|last=Lauter|first=Judith L|author2=P Herscovitch |author3=C Formby |author4=ME Raichle |title=Tonotopic organization in human auditory cortex revealed by positron emission tomography|journal=Hearing Research|volume=20|issue=3|pages=199–205|year=1985|doi=10.1016/0378-5955(85)90024-3|pmid=3878839|s2cid=45928728}}</ref> Tonotopic mapping is preserved throughout most of the audition circuit. The primary auditory cortex receives direct input from the [[medial geniculate nucleus]] of the [[thalamus]] and thus is thought to identify the fundamental elements of music, such as [[Pitch (music)|pitch]] and [[loudness]].

An [[evoked response]] study of congenitally deaf kittens used [[local field potential]]s to measure [[cortical plasticity]] in the auditory cortex. These kittens were stimulated and measured against a control (an un-stimulated congenitally deaf cat (CDC)) and normal hearing cats. The field potentials measured for artificially stimulated CDC were eventually much stronger than that of a normal hearing cat.<ref>{{cite journal|last=Klinke|first=Rainer|author2=Kral, Andrej|author3= Heid, Silvia|author4= Tillein, Jochen|author5= Hartmann, Rainer|s2cid=38985173|title=Recruitment of the auditory cortex in congenitally deaf cats by long-term cochlear electrostimulation|journal=Science|volume=285|issue=5434|pages=1729–33|date=September 10, 1999|doi=10.1126/science.285.5434.1729|pmid=10481008}}</ref> This finding accords with a study by Eckart Altenmuller, in which it was observed that students who received musical instruction had greater cortical activation than those who did not.<ref>{{cite journal|last=Strickland|title=Music and the brain in childhood development|journal=Childhood Education|volume=78|issue=2|pages=100–4|date=Winter 2001|doi=10.1080/00094056.2002.10522714|s2cid=219597861 }}</ref>

The auditory cortex has distinct responses to sounds in the [[Gamma wave|gamma band]]. When subjects are exposed to three or four cycles of a 40 [[hertz]] click, an abnormal spike appears in the [[Electroencephalography|EEG]] data, which is not present for other stimuli. The spike in neuronal activity correlating to this frequency is not restrained to the tonotopic organization of the auditory cortex. It has been theorized that gamma frequencies are [[resonant frequencies]] of certain areas of the brain and appear to affect the visual cortex as well.<ref>{{cite journal|last=Tallon-Baudry|first=C.|author2=Bertrand, O.|title=Oscillatory gamma activity in humans and its role in object representation|journal=Trends in Cognitive Sciences|date=April 1999|volume=3|issue=4|pages=151–162|pmid=10322469|doi=10.1016/S1364-6613(99)01299-1|s2cid=1308261}}</ref> Gamma band activation (25 to 100&nbsp;Hz) has been shown to be present during the perception of sensory events and the process of recognition. In a 2000 study by Kneif and colleagues, subjects were presented with eight musical notes to well-known tunes, such as ''[[Yankee Doodle]]'' and ''[[Frère Jacques]]''. Randomly, the sixth and seventh notes were omitted and an [[electroencephalogram]], as well as a [[magnetoencephalogram]] were each employed to measure the neural results. Specifically, the presence of gamma waves, induced by the auditory task at hand, were measured from the temples of the subjects. The [[Stimulus–response model|omitted stimulus response]] (OSR)<ref>{{Cite journal|last1=Busse|first1=L|last2=Woldorff|first2=M|date=April 2003|title=The ERP omitted stimulus response to "no-stim" events and its implications for fast-rate event-related fMRI designs.|journal=NeuroImage|volume=18|issue=4|pages=856–864|pmid=12725762|doi=10.1016/s1053-8119(03)00012-0|s2cid=25351923}}</ref> was located in a slightly different position; 7&nbsp;mm more anterior, 13&nbsp;mm more medial and 13&nbsp;mm more superior in respect to the complete sets. The OSR recordings were also characteristically lower in gamma waves as compared to the complete musical set. The evoked responses during the sixth and seventh omitted notes are assumed to be imagined, and were characteristically different, especially in the [[Cerebral hemisphere|right hemisphere]].{{citation needed|date=June 2023}} The right auditory cortex has long been shown to be more sensitive to [[tonality]] (high spectral resolution), while the left auditory cortex has been shown to be more sensitive to minute sequential differences (rapid temporal changes) in sound, such as in speech.<ref>{{cite journal |author=Arianna LaCroix |author2=Alvaro F. Diaz |author3=Corianne Rogalsky|title=The relationship between the neural computations for speech and music perception is context-dependent: an activation likelihood estimate study |journal=Frontiers in Psychology |date=2015 |volume=6 |issue=1138 |page=18 |isbn=978-2-88919-911-2 |url=https://books.google.com/books?id=bwEvDwAAQBAJ&q=%22auditory+cortex%22+left+right+speech+music+%22temporal+changes%22+%22spectral+resolution%22&pg=PA18}}</ref>

Tonality is represented in more places than just the auditory cortex; one other specific area is the rostromedial [[prefrontal cortex]] (RMPFC).<ref>{{cite journal|last=Janata|first=P. |author2=Birk, J.L. |author3=Van Horn, J.D. |author4=Leman, M. |author5=Tillmann, B. |author6=Bharucha, J.J. |title=The Cortical Topography of Tonal Structures Underlying Western Music|journal=Science|date=December 2002|volume=298|issue=5601|pages=2167–2170|doi=10.1126/science.1076262|url=http://atonal.ucdavis.edu/publications/papers/Janata_etal_2002_Science.pdf|access-date=11 September 2012|pmid=12481131|bibcode=2002Sci...298.2167J |s2cid=3031759 }}</ref> A study explored the areas of the brain which were active during tonality processing, using [[fMRI]]. The results of this experiment showed preferential [[blood-oxygen-level-dependent]] activation of specific [[voxels]] in RMPFC for specific tonal arrangements. Though these collections of voxels do not represent the same tonal arrangements between subjects or within subjects over multiple trials, it is interesting and informative that RMPFC, an area not usually associated with audition, seems to code for immediate tonal arrangements in this respect. RMPFC is a subsection of the [[medial prefrontal cortex]], which projects to many diverse areas including the [[amygdala]], and is thought to aid in the inhibition of negative [[emotion]].<ref>{{cite journal |last1=Cassel |first1=M. D. |last2=Wright |first2=D. J. |date=September 1986 |title=Topography of projections from the medial prefrontal cortex to the amygdala in the rat |journal=Brain Research Bulletin |volume=17 |issue=3 |pages=321–333 |doi=10.1016/0361-9230(86)90237-6 |pmid=2429740|s2cid=22826730 }}</ref>

Another study has suggested that people who experience 'chills' while listening to music have a higher volume of fibres connecting their auditory cortex to areas associated with emotional processing.<ref>{{cite journal | last1 = Sachs |first1=Matthew E. |last2=Ellis |first2=Robert J. |last3=Schlaug Gottfried |first3=Louie Psyche | year = 2016 | title = Brain connectivity reflects human aesthetic responses to music | journal = Social Cognitive and Affective Neuroscience | volume = 11 | issue = 6| pages = 884–891| doi = 10.1093/scan/nsw009 |pmid=26966157 |pmc=4884308 | doi-access = free }}</ref>

In a study involving [[dichotic listening]] to speech, in which one message is presented to the right ear and another to the left, it was found that the participants chose letters with stops (e.g. 'p', 't', 'k', 'b') far more often when presented to the right ear than the left. However, when presented with phonemic sounds of longer duration, such as vowels, the participants did not favor any particular ear.<ref>{{Cite journal|last1=Jerger|first1=James|last2=Martin|first2=Jeffrey|date=2004-12-01|title=Hemispheric asymmetry of the right ear advantage in dichotic listening|journal=Hearing Research|volume=198|issue=1|pages=125–136|doi=10.1016/j.heares.2004.07.019|pmid=15567609|s2cid=2504300|issn=0378-5955}}</ref> Due to the contralateral nature of the auditory system, the right ear is connected to Wernicke's area, located within the posterior section of the superior temporal gyrus in the left cerebral hemisphere.

Sounds entering the auditory cortex are treated differently depending on whether or not they register as speech. When people listen to speech, according to the strong and weak [[Speech perception#Speech mode hypothesis|speech mode hypotheses]], they, respectively, engage perceptual mechanisms unique to speech or engage their knowledge of language as a whole.