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Auditory cortex

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Auditory cortex
Auditory cortex in thehuman brain
Details
Identifiers
Latincortex auditivus
MeSHD001303
NeuroNames1354
FMA226221
Anatomical terms of neuroanatomy
Coronal sectionof a human brain. BA41(red) and BA42(green) are auditory cortex. BA22(yellow) isBrodmann area 22,HF(blue) ishippocampal formationand pSTG is posterior part ofsuperior temporal gyrus.

Theauditory cortexis the part of thetemporal lobethat processes auditory information in humans and many othervertebrates.It is a part of theauditory system,performing basic and higher functions inhearing,such as possible relations tolanguage switching.[1][2]It is located bilaterally, roughly at the upper sides of thetemporal lobes– in humans, curving down and onto the medial surface, on the superior temporal plane, within thelateral sulcusand comprising parts of thetransverse temporal gyri,and thesuperior temporal gyrus,including the planum polare andplanum temporale(roughlyBrodmann areas 41 and 42,and partially22).[3][4]

The auditory cortex takes part in the spectrotemporal, meaning involving time and frequency, analysis of the inputs passed on from the ear. The cortex then filters and passes on the information to the dual stream of speech processing.[5]The auditory cortex's function may help explain why particular brain damage leads to particular outcomes. For example, unilateral destruction, in a region of the auditory pathway above thecochlear nucleus,results in slight hearing loss, whereas bilateral destruction results incortical deafness.

Structure

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The auditory cortex was previously subdivided into primary (A1) and secondary (A2) projection areas and further association areas. The modern divisions of the auditory cortex are the core (which includes primary auditory cortex, A1), the belt (secondary auditory cortex, A2), and the parabelt (tertiary auditory cortex, A3). The belt is the area immediately surrounding the core; the parabelt is adjacent to the lateral side of the belt.[6]

Besides receiving input from the ears via lower parts of the auditory system, it also transmits signals back to these areas and is interconnected with other parts of the cerebral cortex. Within the core (A1), its structure preservestonotopy,the orderly representation of frequency, due to its ability to map low to high frequencies corresponding to the apex and base, respectively, of thecochlea.

Data about the auditory cortex has been obtained through studies in rodents, cats, macaques, and other animals. In humans, the structure and function of the auditory cortex has been studied usingfunctional magnetic resonance imaging(fMRI),electroencephalography(EEG), andelectrocorticography.[7][8]

Development

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Like many areas in the neocortex, the functional properties of the adult primary auditory cortex (A1) are highly dependent on the sounds encountered early in life. This has been best studied using animal models, especially cats and rats. In the rat, exposure to a single frequency during postnatal day (P) 11 to 13 can cause a 2-fold expansion in the representation of that frequency in A1.[9]Importantly, the change is persistent, in that it lasts throughout the animal's life, and specific, in that the same exposure outside of that period causes no lasting change in the tonotopy of A1. Sexual dimorphism within the auditory cortex can be seen in humans between males in females through the planum temporale, encompassing Wernicke's region, for the planum temporale within males has been observed to have a larger planum temporale volume on average, reflecting previous studies discussing interactions between sex hormones and asymmetrical brain development.[10]

Function

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As with other primary sensory cortical areas, auditory sensations reachperceptiononly if received and processed by acorticalarea. Evidence for this comes fromlesionstudies in human patients who have sustained damage to cortical areas throughtumorsorstrokes,[11]or from animal experiments in which cortical areas were deactivated by surgical lesions or other methods.[12]Damage to the auditory cortex in humans leads to a loss of anyawarenessof sound, but an ability to react reflexively to sounds remains as there is a great deal of subcortical processing in theauditory brainstemandmidbrain.[13][14][15]

Neurons in the auditory cortex are organized according to the frequency of sound to which they respond best.Neuronsat 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 thevisual 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 atonotopic map) likely reflects the fact that thecochleais arranged according to sound frequency. The auditory cortex is involved in tasks such as identifying and segregating "auditoryobjects"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.[16]

Humanbrain scansindicated that a peripheral part of this brain region is active when trying to identifymusical pitch.Individual cells consistently getexcitedby sounds at specific frequencies, ormultiplesof thatfrequency.

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 biologistJames 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."[17]

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]The auditory cortex forms groupings based on fundamentals; in music, for example, this would includeharmony,timing,andpitch.[18]

The primary auditory cortex lies in thesuperior temporal gyrusof the temporal lobe and extends into thelateral sulcusand thetransverse temporal gyri(also calledHeschl's gyri). Final sound processing is then performed by theparietalandfrontallobes of the humancerebral cortex.Animal studies indicate that auditory fields of the cerebral cortex receive ascending input from theauditory thalamusand that they are interconnected on the same and on the oppositecerebral hemispheres.

The auditory cortex is composed of fields that differ from each other in both structure and function.[19]The number of fields varies in different species, from as few as 2 inrodentsto as many as 15 in therhesus 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 inmammals,including primates, used to interpretelectrophysiologicaltests andfunctional imagingstudies of the brain in humans.

When each instrument of asymphony orchestraorjazz bandplays 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 theanterolateralborder of the primary auditory cortex. This location of a pitch-selective area has also been identified in recent functional imaging studies in humans.[20][21]

The primary auditory cortex is subject tomodulationby numerousneurotransmitters,includingnorepinephrine,which has been shown to decreasecellular excitabilityin all layers of thetemporal cortex.Alpha -1 adrenergic receptoractivation, by norepinephrine, decreasesglutamatergicexcitatory postsynaptic potentialsatAMPA receptors.[22]

Relationship to the auditory system

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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—in humans—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 istonotopicallyorganized, which means that neighboring cells in the cortex respond to neighboring frequencies.[23]Tonotopic mapping is preserved throughout most of the audition circuit. The primary auditory cortex receives direct input from themedial geniculate nucleusof thethalamusand thus is thought to identify the fundamental elements of music, such aspitchandloudness.

Anevoked responsestudy of congenitally deaf kittens usedlocal field potentialsto measurecortical plasticityin 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.[24]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.[25]

The auditory cortex has distinct responses to sounds in thegamma band.When subjects are exposed to three or four cycles of a 40hertzclick, an abnormal spike appears in theEEGdata, 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 areresonant frequenciesof certain areas of the brain and appear to affect the visual cortex as well.[26]Gamma band activation (25 to 100 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 asYankee DoodleandFrère Jacques.Randomly, the sixth and seventh notes were omitted and anelectroencephalogram,as well as amagnetoencephalogramwere 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. Theomitted stimulus response(OSR)[27]was located in a slightly different position; 7 mm more anterior, 13 mm more medial and 13 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 theright hemisphere.[citation needed]The right auditory cortex has long been shown to be more sensitive totonality(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.[28]

Tonality is represented in more places than just the auditory cortex; one other specific area is the rostromedialprefrontal cortex(RMPFC).[29]A study explored the areas of the brain which were active during tonality processing, usingfMRI.The results of this experiment showed preferentialblood-oxygen-level-dependentactivation of specificvoxelsin 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 themedial prefrontal cortex,which projects to many diverse areas including theamygdala,and is thought to aid in the inhibition of negativeemotion.[30]

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.[31]

In a study involvingdichotic listeningto 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.[32]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 weakspeech mode hypotheses,they, respectively, engage perceptual mechanisms unique to speech or engage their knowledge of language as a whole.

See also

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This article usesanatomical terminology.

References

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  1. ^Cf. Pickles, James O. (2012).An Introduction to the Physiology of Hearing(4th ed.). Bingley, UK: Emerald Group Publishing Limited, p. 238.
  2. ^Blanco-Elorrieta, Esti; Liina, Pylkkanen (2017-08-16)."Bilingual language switching in the lab vs. in the wild: The Spatio-temporal dynamics of adaptive language control".Journal of Neuroscience.37(37): 9022–9036.doi:10.1523/JNEUROSCI.0553-17.2017.PMC5597983.PMID28821648.
  3. ^Cf. Pickles, James O. (2012).An Introduction to the Physiology of Hearing(4th ed.). Bingley, UK: Emerald Group Publishing Limited, pp. 215–217.
  4. ^Nakai, Y; Jeong, JW; Brown, EC; Rothermel, R; Kojima, K; Kambara, T; Shah, A; Mittal, S; Sood, S; Asano, E (2017)."Three- and four-dimensional mapping of speech and language in patients with epilepsy".Brain.140(5): 1351–1370.doi:10.1093/brain/awx051.PMC5405238.PMID28334963.Open access icon
  5. ^Hickok, Gregory; Poeppel, David (May 2007). "The cortical organization of speech processing".Nature Reviews Neuroscience.8(5): 393–402.doi:10.1038/nrn2113.ISSN1471-0048.PMID17431404.S2CID6199399.
  6. ^Cf. Pickles, James O. (2012).An Introduction to the Physiology of Hearing(4th ed.). Bingley, UK: Emerald Group Publishing Limited, p. 211 f.
  7. ^Moerel, Michelle; De Martino, Federico; Formisano, Elia (29 July 2014)."An anatomical and functional topography of human auditory cortical areas".Frontiers in Neuroscience.8:225.doi:10.3389/fnins.2014.00225.PMC4114190.PMID25120426.
  8. ^Rauschecker, Josef P; Scott, Sophie K (26 May 2009)."Maps and streams in the auditory cortex: nonhuman primates illuminate human speech processing".Nature Neuroscience.12(6): 718–724.doi:10.1038/nn.2331.PMC2846110.PMID19471271.
  9. ^de Villers-Sidani, Etienne; EF Chang; S Bao; MM Merzenich (2007)."Critical period window for spectral tuning defined in the primary auditory cortex (A1) in the rat"(PDF).J Neurosci.27(1): 180–9.doi:10.1523/JNEUROSCI.3227-06.2007.PMC6672294.PMID17202485.
  10. ^Kulynych, J. J.; Vladar, K.; Jones, D. W.; Weinberger, D. R. (March 1994). "Gender differences in the normal lateralization of the supratemporal cortex: MRI surface-rendering morphometry of Heschl's gyrus and the planum temporale".Cerebral Cortex.4(2): 107–118.doi:10.1093/cercor/4.2.107.ISSN1047-3211.PMID8038562.
  11. ^Cavinato, M.; Rigon, J.; Volpato, C.; Semenza, C.; Piccione, F. (January 2012)."Preservation of Auditory P300-Like Potentials in Cortical Deafness".PLOS ONE.7(1): e29909.Bibcode:2012PLoSO...729909C.doi:10.1371/journal.pone.0029909.PMC3260175.PMID22272260.
  12. ^Heffner, H.E.; Heffner, R.S. (February 1986)."Hearing loss in Japanese macaques following bilateral auditory cortex lesions"(PDF).Journal of Neurophysiology.55(2): 256–271.doi:10.1152/jn.1986.55.2.256.PMID3950690.Archived fromthe original(PDF)on 2 August 2010.Retrieved11 September2012.
  13. ^Rebuschat, P.; Martin Rohrmeier, M.; Hawkins, J.A.; Cross, I. (2011).Human subcortical auditory function provides a new conceptual framework for considering modularity.pp. 269–282.doi:10.1093/acprof:oso/9780199553426.003.0028.ISBN978-0-19-955342-6.{{cite book}}:|journal=ignored (help)
  14. ^Krizman, J.; Skoe, E.; Kraus, N. (March 2010)."Stimulus Rate and Subcortical Auditory Processing of Speech"(PDF).Audiology and Neurotology.15(5): 332–342.doi:10.1159/000289572.PMC2919427.PMID20215743.Archived fromthe original(PDF)on 15 April 2012.Retrieved11 September2012.
  15. ^Strait, D.L.; Kraus, N.; Skoe, E.; Ashley, R. (2009)."Musical Experience Promotes Subcortical Efficiency in Processing Emotional Vocal Sounds"(PDF).Annals of the New York Academy of Sciences.1169(1): 209–213.Bibcode:2009NYASA1169..209S.doi:10.1111/j.1749-6632.2009.04864.x.PMID19673783.S2CID4845922.Archived fromthe original(PDF)on 15 April 2012.Retrieved11 September2012.
  16. ^Chechik, Gal; Nelken, Israel (2012-11-13)."Auditory abstraction from spectro-temporal features to coding auditory entities".Proceedings of the National Academy of Sciences of the United States of America.109(46): 18968–18973.Bibcode:2012PNAS..10918968C.doi:10.1073/pnas.1111242109.ISSN0027-8424.PMC3503225.PMID23112145.
  17. ^Beament, James (2001).How We Hear Music: the Relationship Between Music and the Hearing Mechanism.Woodbridge: Boydell Press. p.93.ISBN978-0-85115-813-6.JSTOR10.7722/j.ctt1f89rq1.
  18. ^Deutsch, Diana (February 2010). "Hearing Music in Ensembles".Physics Today.Vol. 63, no. 2. p. 40.doi:10.1063/1.3326988.
  19. ^Cant, NB; Benson, CG (June 15, 2003). "Parallel auditory pathways: projection patterns of the different neuronal populations in the dorsal and ventral cochlear nuclei".Brain Res Bull.60(5–6): 457–74.doi:10.1016/S0361-9230(03)00050-9.PMID12787867.S2CID42563918.
  20. ^Bendor, D; Wang, X (2005)."The neuronal representation of pitch in primate auditory cortex".Nature.436(7054): 1161–5.Bibcode:2005Natur.436.1161B.doi:10.1038/nature03867.PMC1780171.PMID16121182.
  21. ^Zatorre, RJ (2005). "Neuroscience: finding the missing fundamental".Nature.436(7054): 1093–4.Bibcode:2005Natur.436.1093Z.doi:10.1038/4361093a.PMID16121160.S2CID4429583.
  22. ^Dinh, L; Nguyen T; Salgado H; Atzori M (2009). "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".Neurochem Res.34(11): 1896–906.doi:10.1007/s11064-009-9966-z.PMID19357950.S2CID25255160.
  23. ^Lauter, Judith L; P Herscovitch; C Formby; ME Raichle (1985). "Tonotopic organization in human auditory cortex revealed by positron emission tomography".Hearing Research.20(3): 199–205.doi:10.1016/0378-5955(85)90024-3.PMID3878839.S2CID45928728.
  24. ^Klinke, Rainer; Kral, Andrej; Heid, Silvia; Tillein, Jochen; Hartmann, Rainer (September 10, 1999). "Recruitment of the auditory cortex in congenitally deaf cats by long-term cochlear electrostimulation".Science.285(5434): 1729–33.doi:10.1126/science.285.5434.1729.PMID10481008.S2CID38985173.
  25. ^Strickland (Winter 2001). "Music and the brain in childhood development".Childhood Education.78(2): 100–4.doi:10.1080/00094056.2002.10522714.S2CID219597861.
  26. ^Tallon-Baudry, C.; Bertrand, O. (April 1999). "Oscillatory gamma activity in humans and its role in object representation".Trends in Cognitive Sciences.3(4): 151–162.doi:10.1016/S1364-6613(99)01299-1.PMID10322469.S2CID1308261.
  27. ^Busse, L; Woldorff, M (April 2003). "The ERP omitted stimulus response to" no-stim "events and its implications for fast-rate event-related fMRI designs".NeuroImage.18(4): 856–864.doi:10.1016/s1053-8119(03)00012-0.PMID12725762.S2CID25351923.
  28. ^Arianna LaCroix; Alvaro F. Diaz; Corianne Rogalsky (2015)."The relationship between the neural computations for speech and music perception is context-dependent: an activation likelihood estimate study".Frontiers in Psychology.6(1138): 18.ISBN978-2-88919-911-2.
  29. ^Janata, P.; Birk, J.L.; Van Horn, J.D.; Leman, M.; Tillmann, B.; Bharucha, J.J. (December 2002)."The Cortical Topography of Tonal Structures Underlying Western Music"(PDF).Science.298(5601): 2167–2170.Bibcode:2002Sci...298.2167J.doi:10.1126/science.1076262.PMID12481131.S2CID3031759.Retrieved11 September2012.
  30. ^Cassel, M. D.; Wright, D. J. (September 1986). "Topography of projections from the medial prefrontal cortex to the amygdala in the rat".Brain Research Bulletin.17(3): 321–333.doi:10.1016/0361-9230(86)90237-6.PMID2429740.S2CID22826730.
  31. ^Sachs, Matthew E.; Ellis, Robert J.; Schlaug Gottfried, Louie Psyche (2016)."Brain connectivity reflects human aesthetic responses to music".Social Cognitive and Affective Neuroscience.11(6): 884–891.doi:10.1093/scan/nsw009.PMC4884308.PMID26966157.
  32. ^Jerger, James; Martin, Jeffrey (2004-12-01). "Hemispheric asymmetry of the right ear advantage in dichotic listening".Hearing Research.198(1): 125–136.doi:10.1016/j.heares.2004.07.019.ISSN0378-5955.PMID15567609.S2CID2504300.

Check citations 1 & 3..

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