![]() The neurons of the auditory cortex of the brain are able to respond to pitch. 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. What is known about the human auditory cortex comes from a base of knowledge gained from studies in mammals, including primates, used to interpret electrophysiologic tests and functional imaging studies of the brain in humans. ![]() The number, location, and organization of fields in the human auditory cortex are not known at this time. The number of fields varies in different species, from as few as 2 in rodents to as many as 15 in the rhesus monkey. There are additional areas of the human cerebral cortex that are involved in processing sound, in the frontal and parietal lobes.Īnimal 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 hemispheres.The auditory cortex is composed of fields, which differ from each other in both structure and function. The primary auditory cortex is located in the temporal lobe. 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 about the same as Brodmann areas 41 and 42. Individual cells consistently get excited by sounds at specific frequencies, or multiples of that frequency. Human brain scans have indicated that a peripheral bit of this brain region is active when trying to identify musical pitch. The auditory cortex is involved in tasks such as identifying and segregating auditory "objects" and identifying the location of a sound in space. 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. Neurons at one end of the auditory cortex respond best to low frequencies neurons at the other respond best to high frequencies. Neurons in the auditory cortex are organised according to the frequency of sound to which they respond best. ![]() 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. 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 cooling or locally applied drug treatment. ![]()
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