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Tonotopy

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Last Updated: 18 January 2022

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Assessment | Biopsychology | Comparative | Cognitive | Developmental | Language | Individual | Personality | Philosophy | Social | Methods | Statistics | Clinical | Educational | Industrial | Professional items | World psychology | in physiology, tonotopy is spatial arrangement of where sounds of different frequency are process in brain. Tones close to each other in terms of frequency are represented in topologically neighbouring regions in brain. Tonotopic maps are particular case of topographic organization, similar to retinotopy in visual system. Tonotopy in auditory system begins at cochlea, small snail - like structure in inner ear that sends information about sound to brain. Different regions of basilar membrane in organ of Corti, sound - sensitive portion of cochlea, vibrate at different sinusoidal frequencies due to variations in thickness and width along length of membrane. Nerves that transmit information from different regions of basilar membrane encode frequency tonotopically. This tonotopy then projects through vestibulocochlear nerve and associates midbrain structures to primary auditory cortex via auditory radiation pathway. Throughout this radiation, organization is linear with relation to placement on organ of Corti, in accordance to best frequency response of each neuron. However, binaural fusion in superior oliviary complex onward adds significant amounts information encoded in signal strength of each ganglion. Thus, number of tonotopic maps varies between species and degree of binaural synthesis and separation of sound intensities; in humans, six tonotopic maps have been identified in primary auditory cortex. These maps can be generalized by their anatomical locations along auditory cortex. Sounds of low pitch project into aspect of Heschl's gyrus sounds of high pitch project deeply into lateral fissure which houses Heschl's gyrus. Tonotopic map is topographical map of basilar membrane in auditory cortex on Heschl's gyrus.

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* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

History

For all electrodes of stimulation examine, N1 topography of auditory ERPs in Cochlear Implant users was characterized by negative potential field over frontocentral areas associated positive potentials around temporal mastoid sites. This was scalp distribution typical of activity in auditory cortex. Moreover, we find that moving stimulation from to more basal sites of cochlea results in shift of N1 frontocentral negativity toward anterior sites. Such change was associated with alterations in ratio of frontal / temporal potential amplitudes. This results in negativity decrease accompanied by positivity increase on topographic maps. These observations are similar to tonotopic variations of auditory N1 component in response to stimuli from low to high frequencies in normal - hearing subjects. Altogether, our results strongly suggest that, after least 3 months of Cochlear Implant use, recipient's auditory cortex presents tonotopic organization that resembles frequency maps of normal - hearing subjects. This could be shown despite fact that individual potential maps present great intersubject variability, probably because of diversity in size and geometry of cortex in Sylvian fissure, as well as in demographics, and deafness and implantation characteristics. Even if more subjects would be necessary to assert it seems that Tonotopy effects are better defined and more significant for younger patients and those with shorter history of deafness. N1 topographic changes with electrode stimulation were observed over both hemiscalps, but were more significant over ipsilateral hemisphere when all data were considered and more significant over left hemisphere in subjects implanted on right side. This observation was, however, difficult to interpret because, in normal - hearing subjects, it is unclear whether tonotopic maps of auditory cortex are similar to ipsilateral and contralateral or left and right stimulation. As in Bertrand et al. And Verkindt et al., Simple dipolar model was considered to major tonotopic features. This was done essentially in terms of dipole orientations It is known that electrical recording allows more accurate estimation of dipole orientations than dipole locations. As seen in Figure 3, rather vertically oriented dipoles were found to explain N1 wave generated by activation of each electrode. Resultant orientations of this activation follow geometry of folded outer surface of cortex. Stimulation Site Effect Is Clearly Revealed By Dipole Orientation Because Three Of Four Orientation Confidence Intervals Do Not Overlap In Either Hemisphere. This suggests that space, yet different, cortical areas are activate. Confidence intervals on dipole orientations that correspond to electrodes 3, 7, and overlap more than For electrode 15. This fact could be explained by electrode array addressing mostly part of cochlea. Blamey et al. Find that higher acoustically initiated frequencies tend to be by more basal electrodes in opposite ear. Tonotopy should be reorganized easily for high frequencies. However, Dorman et al.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Introduction

Neurons at various levels in Auditory pathway are topographically arranged by their response to different frequencies. This organization, referred to as tonotopy or cochleotopy, mirrors distribution of receptors in cochlea, with gradient extending between neurons that preferentially respond to high frequencies and those that respond best to low frequencies. Many distinct functional areas in auditory system show tonotopic response gradient. In auditory cortex of nonhuman primates, each of three divisions of primary core cortex - A1, R and RT - exhibit tonotopic gradients that are mirror symmetric to each other. Tonotopic gradients have also been demonstrated in lateral and medial belt cortex surrounding core. In contrast to visual cortex, where retinotopic gradients reverse direction at boundary between primary and secondary cortices, receptive field gradients in Auditory cortex run parallel to primary / secondary boundary, such that two mirror symmetric gradients observed in A1 and R extend laterally to belt areas ML and AL as well as medially to areas MM and RM. Exception To This Is Posterior Lateral Gradient In Secondary Belt Area CL, Which Does Not Appear To Extend Into Primary Cortex. Tonotopic organization has been identified in human Auditory cortex using variety of imaging techniques. Majority Of Early Studies Use Only Two Different Stimulus Frequencies. These studies suggest general pattern in which high frequencies activate medial Auditory cortex and low frequencies activate more anterolateral regions in superior temporal plane. This pattern has usually been interpreted as single low - to - high frequency gradient oriented along Heschl's gyrus. Later functional magnetic resonance imaging improved on this design by adding intermediate frequencies, allowing identification of frequency gradients. Results and interpretations these studies have varied considerably. For example, one study single high - to - low gradient extending from posterior medial to anterior lateral Auditory areas, similar to earlier studies. Second Study, However, Describes Two Mirror - Symmetric Frequency Gradients Extending Approximately Along Axis Of HG. In third study, three consistent gradients were report, none of which clearly followed long axis of HG. Finally, authors of fourth study find differences in activation between anterior and posterior HG as well as medial and lateral differences, but conclude that observed activation profile do not represent frequency gradients but instead different functional regions within auditory cortex. Although these imaging studies differ on numerous methodological factors, another potential of variability is interpretation given to observed gradients. Many authors have conceived of these gradients as extending along narrow line between high and low poles. Consideration of data non - human primate studies, however, suggests instead topography composed of alternating high and low frequency bands, each of which extends across contiguous core and belt regions. Woods et AL. Recently, report such pattern and data in terms of non - human primate model, though anterior high - frequency regions do not form continuous band as predicted by primate data.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Sources

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

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