<P> Accumulative converging evidence indicates that the AVS is involved in recognizing auditory objects . At the level of the primary auditory cortex, recordings from monkeys showed higher percentage of neurons selective for learned melodic sequences in area R than area A1, and a study in humans demonstrated more selectivity for heard syllables in the anterior Heschl's gyrus (area hR) than posterior Heshcl's gyrus (area hA1). In downstream associative auditory fields, studies from both monkeys and humans reported that the border between the anterior and posterior auditory fields (Figure 1 - area PC in the monkey and mSTG in the human) processes pitch attributes that are necessary for the recognition of auditory objects . The anterior auditory fields of monkeys were also demonstrated with selectivity for con - specific vocalizations with intra-cortical recordings . and functional imaging One fMRI monkey study further demonstrated a role of the aSTG in the recognition of individual voices . The role of the human mSTG - aSTG in sound recognition was demonstrated via functional imaging studies that correlated activity in this region with isolation of auditory objects from background noise, and with the recognition of spoken words, voices, melodies, environmental sounds, and non-speech communicative sounds . A Meta - analysis of fMRI studies further demonstrated functional dissociation between the left mSTG and aSTG, with the former processing short speech units (phonemes) and the latter processing longer units (e.g., words, environmental sounds). A study that recorded neural activity directly from the left pSTG and aSTG reported that the aSTG, but not pSTG, was more active when the patient listened to speech in her native language than unfamiliar foreign language . Consistently, electro stimulation to the aSTG of this patient resulted in impaired speech perception (see also for similar results). Intra-cortical recordings from the right and left aSTG further demonstrated that speech is processed laterally to music . An fMRI study of a patient with impaired sound recognition (auditory agnosia) due to brainstem damage was also shown with reduced activation in areas hR and aSTG of both hemispheres when hearing spoken words and environmental sounds . Recordings from the anterior auditory cortex of monkeys while maintaining learned sounds in working memory, and the debilitating effect of induced lesions to this region on working memory recall, further implicate the AVS in maintaining the perceived auditory objects in working memory . In humans, area mSTG - aSTG was also reported active during rehearsal of heard syllables with MEG. and fMRI The latter study further demonstrated that working memory in the AVS is for the acoustic properties of spoken words and that it is independent to working memory in the ADS, which mediates inner speech . Working memory studies in monkeys also suggest that in monkeys, in contrast to humans, the AVS is the dominant working memory store . </P> <P> In humans, downstream to the aSTG, the MTG and TP are thought to constitute the semantic lexicon, which is a long - term memory repository of audio - visual representations that are interconnected on the basis of semantic relationships . (See also the reviews by discussing this topic). The primary evidence for this role of the MTG - TP is that patients with damage to this region (e.g., patients with semantic dementia or herpes simplex virus encephalitis) are reported with an impaired ability to describe visual and auditory objects and a tendency to commit semantic errors when naming objects (i.e., semantic paraphasia). Semantic paraphasias were also expressed by aphasic patients with left MTG - TP damage and were shown to occur in non-aphasic patients after electro - stimulation to this region . or the underlying white matter pathway Two meta - analyses of the fMRI literature also reported that the anterior MTG and TP were consistently active during semantic analysis of speech and text; and an intra-cortical recording study correlated neural discharge in the MTG with the comprehension of intelligible sentences . </P> <P> In addition to extracting meaning from sounds, the MTG - TP region of the AVS appears to have a role in sentence comprehension, possibly by merging concepts together (e.g., merging the concept' blue' and' shirt to create the concept of a' blue shirt'). The role of the MTG in extracting meaning from sentences has been demonstrated in functional imaging studies reporting stronger activation in the anterior MTG when proper sentences are contrasted with lists of words, sentences in a foreign or nonsense language, scrambled sentences, sentences with semantic or syntactic violations and sentence - like sequences of environmental sounds . One fMRI study in which participants were instructed to read a story further correlated activity in the anterior MTG with the amount of semantic and syntactic content each sentence contained . An EEG study that contrasted cortical activity while reading sentences with and without syntactic violations in healthy participants and patients with MTG - TP damage, concluded that the MTG - TP in both hemispheres participate in the automatic (rule based) stage of syntactic analysis (ELAN component), and that the left MTG - TP is also involved in a later controlled stage of syntax analysis (P600 component). Patients with damage to the MTG - TP region have also been reported with impaired sentence comprehension . See review for more information on this topic . </P> <P> In contradiction to the Wernicke - Lichtheim - Geschwind model that implicates sound recognition to occur solely in the left hemisphere, studies that examined the properties of the right or left hemisphere in isolation via unilateral hemispheric anesthesia (i.e., the WADA procedure) or intra-cortical recordings from each hemisphere provided evidence that sound recognition is processed bilaterally . Moreover, a study that instructed patients with disconnected hemispheres (i.e., split - brain patients) to match spoken words to written words presented to the right or left hemifields, reported vocabulary in the right hemisphere that almost matches in size with the left hemisphere (The right hemisphere vocabulary was equivalent to the vocabulary of a healthy 11 - years old child). This bilateral recognition of sounds is also consistent with the finding that unilateral lesion to the auditory cortex rarely results in deficit to auditory comprehension (i.e., auditory agnosia), whereas a second lesion to the remaining hemisphere (which could occur years later) does . Finally, as mentioned earlier, an fMRI scan of an auditory agnosia patient demonstrated bilateral reduced activation in the anterior auditory cortices, and bilateral electro - stimulation to these regions in both hemispheres resulted with impaired speech recognition . </P>

The part of the brain mainly responsible for language is the