is anatomically and physiologically split into two regions, the dorsal cochlear nucleus (dcn), and ventral cochlear nucleus (vcn). the vcn is further divided by the nerve root into the posteroventral cochlear nucleus (pvcn) and the anteroventral cochlear nucleus (avcn). trapezoid body main article: trapezoid body the trapezoid body is a bundle of decussating fibers in the ventral pons that carry information used for binaural computations in the brainstem. some of these axons come from the cochlear nucleus and cross over to the other side before traveling on to the superior olivary nucleus. this is believed to help with localization of sound. superior olivary complex main article: superior olivary complex the superior olivary complex is located in the pons, and receives projections predominantly from the ventral cochlear nucleus, although the dorsal cochlear nucleus projects there as well, via the ventral acoustic stria. within the superior olivary complex lies the lateral superior olive (lso) and the medial superior olive (mso). the former is important in detecting interaural level differences while the latter is important in distinguishing interaural time difference. lateral lemniscus in red, as it connects the cochlear nucleus, superior olivary nucleus and the inferior colliculus, seen from behind lateral lemniscus main article: lateral lemniscus the lateral lemniscus is a tract of axons in the brainstem that carries information about sound from the cochlear nucleus to various brainstem nuclei and ultimately the contralateral inferior colliculus of the midbrain. inferior colliculi main article: inferior colliculus the inferior colliculi (ic) are located just below the visual processing centers known as the superior colliculi. the central nucleus of the ic is a nearly obligatory relay in the ascending auditory system, and most likely acts to integrate information (specifically regarding sound source localization from the superior olivary complex and dorsal cochlear nucleus) before sending it to the thalamus and cortex. the inferior colliculus also receives descending inputs from the auditory cortex and auditory thalamus (or medial geniculate nucleus). medial geniculate nucleus main article: medial geniculate nucleus the medial geniculate nucleus is part of the thalamic relay system. primary auditory cortex main article: primary auditory cortex the primary auditory cortex is the first region of cerebral cortex to receive auditory input. perception of sound is associated with the left posterior superior temporal gyrus (stg). the superior temporal gyrus contains several important structures of the brain, including brodmann areas 41 and 42, marking the location of the primary auditory cortex, the cortical region responsible for the sensation of basic characteristics of sound such as pitch and rhythm. we know from research in nonhuman primates that the primary auditory cortex can probably be divided further into functionally differentiable subregions. the neurons of the primary auditory cortex can be considered to have receptive fields covering a range of auditory frequencies and have selective responses to harmonic pitches. neurons integrating information from the two ears have receptive fields covering a particular region of auditory space. the primary auditory cortex is surrounded by secondary auditory cortex, and interconnects with it. these secondary areas interconnect with further processing areas in the superior temporal gyrus, in the dorsal bank of the superior temporal sulcus, and in the frontal lobe. in humans, connections of these regions with the middle temporal gyrus are probably important for speech perception. the frontotemporal system underlying auditory perception allows us to distinguish sounds as speech, music, or noise. the auditory ventral and dorsal streams main article: language processing in the brain further information: two-streams hypothesis § two auditory systems dual stream connectivity between the auditory cortex and frontal lobe of monkeys and humans. top: the auditory cortex of the monkey (left) and human (right) is schematically depicted on the supratemporal plane and observed from above (with the parieto- frontal operculi removed). bottom: the brain of the monkey (left) and human (right) is schematically depicted and displayed from the side. orange frames mark the region of the auditory cortex, which is displayed in the top sub-figures. top and bottom: blue colors mark regions affiliated with the ads, and red colors mark regions affiliated with the avs (dark red and blue regions mark the primary auditory fields). abbreviations: amyg-amygdala, hg-heschl's gyrus, fef-frontal eye field, ifg-inferior frontal gyrus, ins-insula, ips-intra parietal sulcus, mtg-middle temporal gyrus, pc-pitch center, pmd-dorsal premotor cortex, pp-planum polare, pt-planum temporale, tp-temporal pole, spt-sylvian parietal-temporal, pstg/mstg/astg-posterior/middle/anterior superior temporal gyrus, cl/ ml/al/rtl-caudo-/middle-/antero-/rostrotemporal-lateral belt area, cpb/rpb-caudal/rostral parabelt fields. used with permission from poliva o. from where to what: a neuroanatomically based evolutionary model of the emergence of speech in humans. material was copied from this source, which is available under a creative commons attribution 4.0 international license. from the primary auditory cortex emerge two separate pathways: the auditory ventral stream and auditory dorsal stream. the auditory ventral stream includes the anterior superior temporal gyrus, anterior superior temporal sulcus, middle temporal gyrus and temporal pole. neurons in these areas are responsible for sound recognition, and extraction of meaning from sentences. the auditory dorsal stream includes the posterior superior temporal gyrus and sulcus, inferior parietal lobule and intra-parietal sulcus. both pathways project in humans to the inferior frontal gyrus. the most established role of the auditory dorsal stream in primates is sound localization. in humans, the auditory dorsal stream in the left hemisphere is also responsible for speech repetition and articulation, phonological long-term encoding of word names, and verbal working memory. clinical significance proper function of the auditory system is required to able to sense, process, and understand sound from the surroundings. difficulty in sensing, processing and understanding sound input has the potential to adversely impact an individual's ability to communicate, learn and effectively complete routine tasks on a daily basis. in children, early diagnosis and treatment of impaired auditory system function is an important factor in ensuring that key social, academic and speech/language developmental milestones are met. impairment of the auditory system can include any of the following: auditory brainstem response and abr audiometry test for newborn hearing auditory processing disorder hyperacusis health effects due to noise tinnitus endaural phenomena