Primary auditory cortex
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{{Infobox Brain|
Name = Primary auditory cortex |
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Image = brodmann_41_42.png |
Caption = Brodmann areas 41 & 42 of the human brain. |
Image2 = Brain Surface Gyri.SVG |
Caption2 = The Primary Auditory Cortex is highlighted in magenta, and has been known to interact with all areas highlighted on this neural map. |
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Artery = |
Vein = |
Acronym = |
BrainInfoType = ancil |
BrainInfoNumber = 428 |
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}}
The '''primary auditory cortex''' is the region of the [[brain]] that is responsible for processing of [[auditory system|auditory]] ([[sound]]) information.
==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 study|lesion studies]] in human patients who have sustained damage to cortical areas through [[tumor]]s or [[stroke]]s, or from animal experiments in which cortical areas were deactivated by cooling or locally applied drug treatment. Damage to the Primary 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 brainstem]] and [[midbrain]].
Neurons in the auditory cortex are organised 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 tonotopic map) is unknown and is likely to reflect the fact that the sensory epithelium of the auditory system, 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.
Human [[brain scan]]s have indicated that a peripheral bit of this brain region is active when trying to identify [[musical pitch]]. Individual cells consistently get excited by sounds at specific frequencies, or [[frequency multiple|multiple]]s of that [[frequency]].
The primary auditory cortex is about the same as [[Brodmann area]]s 41 and 42. It lies in the posterior half of the [[superior temporal gyrus]] and also dives into the [[lateral sulcus]] as the [[transverse temporal gyri]] (also called ''Heschl's gyri'').
The primary auditory cortex is located in the [[temporal lobe]]. There are additional areas of the human [[cerebral cortex]] that are involved in processing sound, in the [[frontal]] and [[parietal lobe]]s.
Animal studies indicate that auditory fields of the cerebral cortex receive ascending input from the [[auditory thalamus]], and that they are interconnected on the same ''and'' on the opposite [[cerebral hemisphere]]s.The auditory cortex is composed of fields, which differ from each other in both structure and function.<ref>{{cite journal
| last =Cant
| first =NB
| authorlink =
| coauthors =
| 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
| publisher =
| date =[[June 15]], [[2003]]
| url =http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6SYT-482YJ98-M&_user=1458830&_coverDate=06%2F15%2F2003&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000052790&_version=1&_urlVersion=0&_userid=1458830&md5=1de05023dc9cefd1b22fcc993ef3d4aa
| doi =10.1016/S0361-9230(03)00050-9
| id =
| accessdate = }}</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 [[electrophysiologic test]]s and [[functional imaging]] studies of the brain in humans.
When each instrument of the [[symphony orchestra]] or the [[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 [[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
| authorlink =
| coauthors =Wang, X
| title =The neuronal representation of pitch in primate auditory cortex
| journal =Nature
| volume =436
| issue =7054
| pages =1161–5
| publisher =
| date =2005
| url =http://www.nature.com/nature/journal/v436/n7054/full/nature03867.html
| doi =10.1038/nature03867
| id =
| accessdate = }}</ref><ref>{{cite journal
| last =Zatorre
| first =RJ
| authorlink =
| coauthors =
| title =Neuroscience: finding the missing fundamental
| journal =Nature
| volume =436
| issue =7054
| pages =1093–4
| publisher =
| date =2005
| url =http://www.nature.com/nature/journal/v436/n7054/full/4361093a.html
| doi =10.1038/4361093a
| id =
| accessdate = }}</ref>
The auditory cortex does not just receive input from lower centers and the ear, but also provides it.
==Brodmann area 41==
This area is also known as '''anterior transverse temporal area 41 (H)'''. It is a subdivision of the [[cytoarchitecture|cytoarchitecturally]]-defined [[temporal lobe|temporal]] region of [[cerebral cortex]], occupying the [[anterior transverse temporal gyrus]] (H) in the bank of the [[lateral sulcus]] on the dorsal surface of the [[temporal lobe]]. Brodmann area 41 is bounded medially by the [[parainsular area 52]] (H) and laterally by the [[posterior transverse temporal area 42]] (H) (Brodmann-1909).
==Brodmann area 42==
This area is also known as '''posterior transverse temporal area 42 (H)'''. It is a subdivision of the cytoarchitecturally-defined temporal region of cerebral cortex, located in the bank of the lateral sulcus on the dorsal surface of the temporal lobe. Brodmann area 42 is bounded medially by the [[anterior transverse temporal area 41]] (H) and laterally by the [[superior temporal area 22]] (Brodmann-1909).
==Relationship to auditory system==
[[Image:Gray756.png|thumb|300px|Areas of localization on lateral surface of hemisphere. Motor area in red. Area of general sensations in blue. Auditory area in green. Visual area in yellow.]]
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 AC in the middle and the tertiary AC on the outside.
The primary auditory cortex is [[wikt:tonotopically|tonotopically]] organized, which means that certain cells in the auditory cortex are sensitive to specific frequencies. This is a fascinating function which has been preserved throughout most of the audition circuit. This area of the brain “is thought to identify the fundamental elements of music, such as [[Pitch (music)|pitch]] and loudness. This makes sense as this is the area which receives direct input from the [[medial geniculate nucleus]] of the [[thalamus]]. The [[secondary auditory cortex]] has been indicated in the processing of “harmonic, melodic and rhythmic patterns.” The [[tertiary auditory cortex]] supposedly integrates everything into the overall experience of music.<ref>[http://www.nature.com/nature/journal/v416/n6876/full/416012a.html Access : : Nature<!-- Bot generated title -->]</ref>
An [[evoked response]] study of congenitally deaf kittens by Klinke et al. utilized [[field potentials]] to measure [[cortical plasticity]] in the auditory cortex. These kittens were stimulated and measured against a control or un-stimulated congenitally deaf cat (CDC) and normal hearing cats. The field [[potential]]s measured for artificially stimulated CDC was eventually much stronger than that of a normal hearing cat.<ref>{{cite journal
| last =Klinke
| first =Rainer
| authorlink =
| coauthors = Kral, Andrej; Heid, Silvia ; Tillein, Jochen ; Hartmann , Rainer
| title =Recruitment of the auditory cortex in congenitally deaf cats by long-term cochlear electrostimulation
| journal =Science
| volume =285
| issue =5434
| pages =1729–33
| publisher =
| date =[[September 10]], [[1999]]
| url =http://www.sciencemag.org/cgi/content/abstract/285/5434/1729
| doi =10.1126/science.285.5434.1729
| id =
| accessdate =
| pmid =10481008 }}</ref> This is in concordance with Eckart Altenmuller’s study where it was observed that students who received musical instruction had greater cortical activation than those who did not.<ref>{{cite journal
| last =Strickland
| first =
| authorlink =
| coauthors =
| title =Music and the brain in childhood development
| journal =Childhood Education
| volume =78
| issue =2
| pages =100–4
| publisher =
| date =Winter 2001
| url =
| doi =
| id =
| accessdate = }}</ref>
The auditory cortex exhibits some strange behavior pertaining to the [[gamma wave]] frequency. When subjects are exposed to three or four cycles of a 40 [[hertz]] click, an abnormal [[spik]]e 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 this is a “[[resonant frequency]]” of certain areas of the brain, and appears to affect the visual cortex as well.<ref>{{cite journal
| last =Bertrand
| first = O.
| authorlink =
| coauthors =Tallon-Baudry, C.; Fischer, C.; and Pernier, J.
| title =Object representation and gamma oscillations
| journal =
| volume =
| issue =
| pages =
| publisher =
| date =
| url =http://biomag2000.hut.fi/papers/0001.pdf
| doi =
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| accessdate = }}</ref>
[[Gamma band activation]] (20 to 40 Hz) has been shown to be present during the perception of sensory events and the process of recognition. Kneif et al, in their 2000 study, presented subjects with eight musical notes to well known tunes, such as ''[[Yankee Doodle]]'' and ''[[Frere 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 OSP response, or [[omitted stimulus response]], 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 OSP 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]].<ref>{{cite journal
| last =Knief
| first =A.
| authorlink =
| coauthors =Schulte, M.; Fujiki, N.; and Pantev, C.
| title =Oscillatory Gamma band and Slow brain Activity Evoked by Real and Imaginary Musical Stimuli
| journal =
| volume =
| issue =
| pages =
| publisher =
| date =
| url =
| doi =
| id =
| accessdate = }}</ref> The right auditory cortex has long been shown to be more sensitive to [[tonality]], while the left auditory cortex has been shown to be more sensitive to minute sequential differences in sound specifically speech.
[[Hallucinations]] have been shown to produce [[oscillation]]s which are parallel (although not exactly the same as) the gamma frequency range. Sperling showed in his 2004 study that auditory hallucinations produce band wavelengths in the range of 12.5-30 Hz. The bands occurred in the left auditory cortex of a [[schizophrenia|schizophrenic]] and were controlled against 13 controls (18) . This aligns with the studies of people remembering a song in their minds; they do not perceive any sound, but experience the [[melody]], [[rhythm]] and overall experience of [[sound]]. When schizophrenics experience hallucinations, it is the primary auditory cortex which becomes active. This is characteristically different from remembering a sound stimulus, which only faintly activates the tertiary auditory cortex.<ref>Abbott, Alison Music, maestro, please! Nature v. 416 no. 6876 (March 7 2002)</ref> By deduction, an artificial stimulation of the primary auditory cortex should elicit an incredibly real auditory hallucination. The termination of all audition and [[music]] into the tertiary auditory cortex creates a fascinating nexus of aural information. If this theory is true, it would be interesting to study a subject with a damaged, TAC or one with artificially suppressed function. This would be very difficult to do as the tertiary cortex is simply a ring around the secondary, which is a ring around the primary AC.
[[pitch (music)|Tone]] is perceived in more places than just the auditory cortex; one specifically fascinating area is the rostromedial [[prefrontal cortex]].<ref>Petr Janata et al. The Cortical Topography of Tonal Structures Underlying Western Music. Science, Vol 298, Issue 5601, 2167-2170 , 13 December 2002</ref> Janata et al, in their 2002 study, explored the areas of the brain which were active during tonality processing, by means of the [[fMRI]] technique. The result of which displayed several areas which are not normally considered to be part of the audition process. The rostromedial prefrontal cortex is a subsection of the [[medial prefrontal cortex]], which projects to the [[amygdala]], and is thought to aid in the inhibition of negative [[emotion]].<ref>Cassel, Topography of projections from the medial prefrontal cortex to the amygdala in the rat. Brain Res Bull. 1986 Sep;17(3):321-33</ref> The medial prefrontal cortex is thought to be the core developmental difference between the impulsive teenager and the calm adult. The [[rostromedial prefrontal cortex]] is tonality sensitive, meaning it is activated by the tones and frequencies of [[resonant]] sounds and music. It could be hypothesized that this is the mechanism by which music ameliorates the soul (or, if one prefers, the [[limbic system]]).
==See also==
* [[Auditory system]]
* [[Brodmann area]]
* [[Noise health effects]]
==References==
<references/>
==External links==
* {{BrainInfo|ancil|77}}: area 41
* {{BrainInfo|ancil|78}}: area 42
* {{BrainMaps|primary%20auditory%20cortex|primary auditory cortex}}
{{auditory system}}
{{Prosencephalon}}
[[Category:Auditory system]]
[[Category:Cerebrum]]
[[de:Auditiver Cortex]]
[[nl:Auditieve cortex]]
[[ja:一次聴覚野]]