Primary auditory cortex10/29/2022 ![]() ![]() Referring to Figure 53-5B, note that the basilar membrane near the base of the cochlea is stimulated by sounds of all frequencies and, in the cochlear nuclei, this same breadth of sound representation is found. The frequency range to which each individual neuron in the auditory cortex responds is much narrower than that in the cochlear and brain stem relay nuclei. Other auditory cortex areas detect special qualities, such as the sudden onset of sounds, or perhaps special modulations, such as noise versus pure frequency sounds. Another map is probably used to detect the direction from which the sound comes. For example, one of the large maps in the primary auditory cortex almost certainly discriminates the sound frequencies and gives the person the psychic sensation of sound pitches. Why does the auditory cortex have so many different tonotopic maps? The answer, presumably, is that each of the separate areas dissects out some specific feature of the sounds. In most maps, the low-frequency sounds are located anteriorly, as shown in Figure 53-10, and the high-frequency sounds are located posteriorly. ![]() In each of these maps, high-frequency sounds excite neurons at one end of the map, whereas low-frequency sounds excite neurons at the opposite end. Hall PhD, in Guyton and Hall Textbook of Medical Physiology, 2021 Sound Frequency Perception in the Primary Auditory CortexĪt least six tonotopic maps have been described in the primary auditory cortex and auditory association areas. The primary vestibular cortex in humans is thought to occupy a region just posterior to the primary somatosensory cortex in the parietal cortex. Movements and positions of the head are monitored primarily by the vestibular system. The auditory association cortex (Brodmann areas 22 and 42), which is concerned with the memory and classification of sounds, is inferior and posterior to the primary auditory cortex, along the superior bank of the middle temporal gyrus. Moreover, it is organized tonotopically (the anterior auditory cortex receives signals initiated by sounds with higher frequencies, whereas the posterior cortex receives lower frequency sounds) to enable the discrimination of the pitch of sounds. Similar to other sensory cortices, the primary auditory cortex is organized in columns, such that each column of cells responds maximally to an acoustic stimulus of a specific frequency. 6B Brodmann area 41) is located along the upper bank of the superior temporal gyrus, within the lateral sulcus on two gyri known as Heschl's gyri. Topolovec, in Encyclopedia of the Human Brain, 2002 V.C. If the auditory association cortex of area 22 is damaged in the dominant hemisphere, severe language problems ensue, as discussed later in this chapter.ĭavid F. An individual with such damage may have some difficulty localizing sounds on the contralateral side and may have some subtle hearing loss that is greater for the contralateral ear, but the deficits are not nearly comparable in magnitude to those that follow unilateral damage to somatosensory or visual cortex. As a result, even total destruction of auditory cortex on one side has relatively little effect on hearing. Area 42 is flanked by area 22, which forms much of the superior temporal gyrus and is called the auditory association cortex.Īt levels rostral to the cochlear nuclei, both ears are represented in the auditory pathway of each side of the brain, although the contralateral ear predominates (see Chapter 14). This is analogous to the arrangement found in the second somatosensory area (S2), so area 42 is often referred to as A2. Area 42 is adjacent to area 41 and receives auditory information from area 41 and the medial geniculate nucleus. Just as the body is mapped onto the postcentral gyrus (somatotopy) and the retina is mapped onto striate cortex (retinotopy), the spectrum of audible frequencies is mapped onto area 41 ( tonotopy see Fig. Area 41 is granular cortex (like areas 3 and 17) and receives most of the auditory radiation from the medial geniculate nucleus via the sublenticular part of the internal capsule thus it serves as primary auditory cortex, or A1 ( Fig. 14.18) cross the posterior part of this surface and form Brodmann's areas 41 and 42. One or two transverse temporal gyri (of Heschl see Fig. The superior surface of the temporal lobe forms one wall of the lateral sulcus. Vanderah PhD, in Nolte's The Human Brain, 2021 Primary Auditory Cortex Is in the Temporal Lobe ![]()
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