Auditory Cortex Is Made up of Multiple Fields to Carry out Parallel and Serial Processing

In all mammals studied, auditory cortex is made up of multiple fields, which are distinguished from one another on both anatomical and functional grounds. The number of such fields varies among species studied from as few as 2 in rodents to as many as 15 in the rhesus monkey. The number, location, and organization of such fields in the human are not fully known. It would be highly desirable, however, to know the functional and structural counterparts of human and monkey auditory cortex. Although much less is known about the functional organization of temporal auditory cortex in the human than in the monkey, from available data there are some striking anatomical similarities between the two species. These data, together with modern imaging [functional magnetic resonance imaging (fMRI) and positron emission tomography (PET)] and direct [electrocorticography (ECoG)] and indirect [electroencephalography (EEG) and magnetoencephalography (MEG)] electrophysio-logical recording data in humans, enable us to tentatively apply to the human a model of functional organization of auditory cortex developed for the monkey. Figure 6C shows a schematic representation of monkey auditory cortex based on modern anatomical and physiological studies. Primary auditory cortex is combined with adjacent cortex to form a core area. Surrounding the core auditory cortex is an auditory belt area, and around that is a parabelt region. The belt and parabelt areas are often referred to as secondary or associational areas. Figures 6A and 6B show two views of the human brain showing the general locations and extent of what may be equivalent core, belt, and parabelt areas in the human. There is general agreement about the location, extent, and tonotopic organization of the human primary auditory field (AI), on the mesial aspect of Heschl's gyrus (HG). There is less agreement about the organization of surrounding auditory. Whether this monkey model is adequate to describe the human auditory cortex is yet to be determined. Currently, however, it provides a tool for further exploration using modern recording and imaging technology.

We know from animal studies that auditory fields receive ascending input from the auditory thalamus, that they are richly interconnected on the same and opposite cerebral hemispheres, and that they provide afferent input to the MGB and IC as part of a massive parallel descending system of pathways that eventually reaches the lower auditory brain stem and the cochlea (Fig. 5). These auditory cortical areas are confined to temporal cortex and serve primarily a sensory function. This means that their neurons and neuronal circuits are sensitive mainly to changes in physical parameters of a suprathreshold acoustic signal reaching the ears, and thus they are designed to detect, discriminate, identify, and localize sound sources. Multiple auditory areas are thought to represent hierarchical processing levels. Some areas involved in higher order processing of acoustic stimuli, such as speech, lie outside of these ''classic'' auditory fields, on the frontal and parietal lobes.

Understanding And Treating Autism

Understanding And Treating Autism

Whenever a doctor informs the parents that their child is suffering with Autism, the first & foremost question that is thrown over him is - How did it happen? How did my child get this disease? Well, there is no definite answer to what are the exact causes of Autism.

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