As with other primary sensory cortical areas,<unk>  sensations reach perception only if received and processed by a cortical area. Evidence for this comes from lesion studies in human patients who have sustained damage to cortical areas through tumors or strokes, or from animal experiments in which cortical areas were deactivated by surgical lesions or other methods. Damage to the<unk>  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<unk>  brainstem and midbrain. Neurons in the<unk>  are organized<unk> cording to the frequency of sound to which they respond best. Neurons at one end of the<unk>  respond best to low frequencies; neurons at the other respond best to high frequencies. There are multiple<unk>  areas (much like the multiple areas in the visual<unk> , 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) likely reflects the fact that the cochlea is arranged<unk> cording to sound frequency. The<unk>  is involved in tasks such as identifying and segregating<unk>  objects" and identifying the location of a sound in space. For example, it has been shown that A1 encodes complex and abstract aspects of<unk>  stimuli without encoding their "raw" aspects like frequency content, presence of a distinct sound or its echoes. Human brain scans indicated that a peripheral part of this brain region is<unk> tive when trying to identify musical pitch. Individual cells consistently get excited by sounds at specific frequencies, or multiples of that frequency. The<unk>  plays an important yet ambiguous role in hearing. When the<unk>  information passes into the<unk> , the specifics of what exactly takes place are unclear. There is a large degree of individual variation in the<unk> , as noted by English biologist James Beament, who wrote, “The<unk>  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." In the hearing process, multiple sounds are transduced simultaneously. The role of the<unk>  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. The<unk>  forms groupings based on fundamentals; in music, for example, this would include harmony, timing, and pitch. The primary<unk>  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 and frontal lobes of the human cerebral<unk> . Animal studies indicate that<unk>  fields of the cerebral<unk>  receive ascending input from the<unk>  thalamus and that they are interconnected on the same and on the opposite cerebral hemispheres. The<unk>  is composed of fields that differ from each other in both structure and function. The number of fields varies in different species, from as few as 2 in rodents to as many as 15 in the rhesus monkey. The number, location, and organization of fields in the human<unk>  are not known at this time. What is known about the human<unk>  comes from a base of knowledge gained from studies in mammals, including primates, used to interpret 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<unk>  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<unk> . This location of a pitch-selective area has also been identified in recent functional imaging studies in humans. The primary<unk>  is subject to modulation by numerous neurotransmitters, including norepinephrine, which has been shown to decrease cellular excitability in all layers of the temporal<unk> . alpha-1 adrenergic receptor<unk> tivation, by norepinephrine, decreases glutamatergic excitatory postsynaptic potentials at AMPA receptors. Relationship to the<unk>  system Areas of localization on lateral surface of hemisphere. Motor area in red. Area of general sensations in blue.<unk>  area in green. Visual area in yellow. The<unk>  is the most highly organized processing unit of sound in the brain. This<unk>  area is the neural crux of hearing, and—in humans—language and music. The<unk>  is divided into three separate parts: the primary, secondary, and tertiary<unk> . These structures are formed concentrically around one another, with the primary<unk>  in the middle and the tertiary<unk>  on the outside. The primary<unk>  is tonotopically organized, which means that neighboring cells in the<unk>  respond to neighboring frequencies. Tonotopic mapping is preserved throughout most of the audition circuit. The primary<unk>  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 and loudness. An evoked response study of congenitally deaf kittens used local field potentials to measure cortical plasticity in the<unk> . 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. This finding<unk> cords with a study by Eckart Altenmuller, in which it was observed that students who received musical instruction had greater cortical<unk> tivation than those who did not. The<unk>  has distinct responses to sounds in the gamma band. When subjects are exposed to three or four cycles of a 40 hertz click, an abnormal spike appears in the EEG data, which is not present for other stimuli. The spike in neuronal<unk> tivity correlating to this frequency is not restrained to the tonotopic organization of the<unk> . It has been theorized that gamma frequencies are resonant frequencies of certain areas of the brain and appear to affect the visual<unk>  as well. Gamma band<unk> tivation (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 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<unk>  task at hand, were measured from the temples of the subjects. The omitted stimulus response (OSR) 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 the right hemisphere. The right<unk>  has long been shown to be more sensitive to tonality (high spectral resolution), while the left<unk>  has been shown to be more sensitive to minute sequential differences (rapid temporal changes) in sound, such as in speech. Tonality is represented in more places than just the<unk> ; one other specific area is the rostromedial prefrontal<unk>  (RMPFC). A study explored the areas of the brain which were<unk> tive during tonality processing, using fMRI. The results of this experiment showed preferential blood-oxygen-level-dependent<unk> tivation 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<unk> , which projects to many diverse areas including the amygdala, and is thought to aid in the inhibition of negative emotion. Another study has suggested that people who experience 'chills' while listening to music have a higher volume of fibres connecting their<unk>  to areas associated with emotional processing. 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
Auditory cortex
Barrel cortex
Postrhinal cortex
Language center
Olfactory tract
Brodmann area
Optic stalk
Olfactory trigone