We used magnetoencephalography (MEG) to measure the auditory evoked magnetic field (AEF), which reflects language-related performance. The aim of this study was to investigate how this neurophysiological index in each hemisphere is correlated with language performance in autism spectrum disorder (ASD) and TD children. Using the child-customised MEG device, we previously reported that language-related performance was reflected in the strength of the early component (P50m) of the auditory evoked magnetic field (AEF) in typically developing (TD) young children (2 to 5 years old). Recently, a child-customised MEG device has facilitated the acquisition of bi-hemispheric recordings, even in young children. In young children, however, the simultaneous quantification of the bilateral auditory-evoked response during binaural hearing is difficult using conventional adult-sized MEG systems. ![]() Indeed, Wernicke's area, which is critical to the comprehension of human language, lies within the secondary auditory area ( Figure 13.15 see also Chapter 27).Magnetoencephalography (MEG) is used to measure the auditory evoked magnetic field (AEF), which reflects language-related performance. It seems likely, therefore, that specific regions of the human auditory cortex are specialized for processing elementary speech sounds, as well as other temporally complex acoustical signals, such as music. ![]() Studies of human patients with bilateral damage to the auditory cortex also reveal severe problems in processing the temporal order of sounds. Thus, without the auditory cortex, monkeys cannot discriminate one conspecific communication sound from another. If the auditory cortex is ablated in these animals, they lose the ability to discriminate between two complex sounds that have the same frequency components but which differ in temporal sequence. Behavioral studies in cats and monkeys show that the auditory cortex is especially important for processing temporal sequences of sound. In humans, the best example of such time-varying signals is speech, where different phonetic sequences are perceived as distinct syllables and words. Sounds that are especially important for intraspecific communication often have a highly ordered temporal structure. The primary auditory cortex (A1) is (more.) (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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