(A) Diagram showing the brain in left lateral view, including the depths of the lateral sulcus, where part of the auditory cortex occupying the superior temporal gyrus normally lies hidden. It appears that some areas are specialized for processing combinations of frequencies, while others are specialized for processing modulations of amplitude or frequency. The sorts of sensory processing that occur in the other divisions of the auditory cortex are not well understood, but they are likely to be important to higher- order processing of natural sounds, including those used for communication. ![]() The EE and EI stripes alternate, an arrangement that is reminiscent of the ocular dominance columns in V1 (see Chapter 12). ![]() The neurons in one stripe are excited by both ears (and are therefore called EE cells), while the neurons in the next stripe are excited by one ear and inhibited by the other ear (EI cells). Orthogonal to the frequency axis of the tonotopic map is a striped arrangement of binaural properties. Thus, A1 is said to comprise a tonotopic map, as do most of the ascending auditory structures between the cochlea and the cortex. Unlike the visual and somatic sensory systems, however, the cochlea has already decomposed the acoustical stimulus so that it is arrayed tonotopically along the length of the basilar membrane. The primary auditory cortex (A1) has a topographical map of the cochlea ( Figure 13.14), just as the primary visual cortex (V1) and the primary somatic sensory cortex (S1) have topographical maps of their respective sensory epithelia. The belt areas of the auditory cortex receive more diffuse input from the belt areas of the medial geniculate complex and therefore are less precise in their tonotopic organization. The primary auditory cortex ( A1) is located on the superior temporal gyrus in the temporal lobe and receives point-to-point input from the ventral division of the medial geniculate complex thus, it contains a precise tonotopic map. Although the auditory cortex has a number of subdivisions, a broad distinction can be made between a primary area and peripheral, or belt, areas. ![]() The ultimate target of afferent auditory information is the auditory cortex.
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