Anatomical Organization of the Auditory CortexDOI: 10.3766/jaaa.19.10.5Troy A. Hackett*AbstractThe identification of areas that contribute to auditory processing in the human cerebral cortex has beenthe subject of sporadic investigation for more than one century. Several anatomical schemas have beenadvanced, but a standard model has not been adopted by researchers in the field. Most often, the resultsof functional imaging or electrophysiological studies involving auditory cortex are related to thecytoarchitectonic map of Brodmann (1909). Though useful as a guide and point of reference, this maphas never been validated and appears to be incomplete. In recent years, renewed interest in theorganization of auditory cortex has fostered numerous comparative studies in humans, nonhumanprimates, and other mammalian species. From these efforts, common features of structural andfunctional organization have begun to emerge from which a working model of human auditory cortex canbe derived. The results of those studies and the rudiments of the model are reviewed in this manuscript.Key Words: Anatomy, cerebral cortex, hearing, pathway, primateAbbreviations: LS 5 lateral sulcus (Sylvian fissure); MGd5 medial geniculate, dorsal division; MGv 5medial geniculate, ventral division; STG 5 superior temporal gyrus; TTG 5 transverse temporal gyrusSumarioLa identificacio´n de a´ reas que contribuyen al procesamiento auditivo en el corteza cerebral humana hasido un tema de investigacio´n espora´dica por ma´ s de un siglo. Varios esquemas anato´micos han sidopresentados, pero los investigadores en el campo no han adoptado un modelo esta´ ndar. Ma´s amenudo, los resultados de ima´ genes funcionales y de estudios electrofisiolo´ gicos involucrando lacorteza cerebral se ha relacionado con el mapa cito-arquitecto´ nico de Brodmann (1909). Aunque u´ tilcomo guı´a y por sus puntos de referencia, este mapa nunca ha sido validado y parece estar incompleto.En an˜ os recientes, un intere´s renovado por la organizacio´ n de la corteza auditiva ha promovidonumerosos estudios comparativos en humanos, en primates no humanos y otras especies demamı´feros. De estos esfuerzos, rasgos comunes de organizacio´ n estructural y funcional han empezadoa emerger, a partir de los cuales puede derivarse un modelo de trabajo de la corteza auditiva humana.Los resultados de estos estudios y los rudimentos del modelo se revisan en este artı´culo.Palabras Clave: Anatomı´a, corteza cerebral, audicio´n, vı´a, primateAbreviaturas: LS 5 surco lateral (fisura de Silvio); MGd 5 geniculado medial, divisio´ n dorsal; MGv 5geniculado ventral, divisio´ n ventral; STG 5 giro temporal superior; TTG 5 giro temporal transversoThe long-term goal of our research program is todevelop a comprehensive description of humanauditory cortex organization. What are itsstructural components, and what are their functions?How do these elements work together to produce theperceptual experience of hearing? Research in humansand other mammals indicates that the auditory cortexis comprised of an interconnected group of distinctareas, but the number of areas involved and theirconnections are unknown for humans. A testableworking model of human auditory cortex has not beendeveloped, even though such models have beendeveloped for other species. Early descriptions of theauditory cortex include several anatomical and lesionstudies conducted in the late 1800s and early 1900s(Broca, 1865; Wernicke, 1874; Ferrier, 1875; Brod-mann, 1905, 1909; von Economo and Koskinas, 1925;Beck, 1928, 1929; von Economo and Horn, 1930;Poljak, 1932; Clark, 1936; Walker, 1937; von Bonin,1938). These classic studies localized auditory cortex tothe superior temporal gyrus of humans and nonhumanprimates and remain influential even today. ForTroy A. Hackett, Vanderbilt University, 301 Wilson Hall, 111 21stAvenue South, Nashville, TN 37203; Phone: 615-322-7491; E-mail:[email protected] research was supported by NIH/NIDCD grant R01 DC04318.*Department of Hearing and Speech Sciences, Department of Psychology, Vanderbilt University School of MedicineJ Am Acad Audiol 19:774–779 (2008)774example, the nomenclature derived from Brodmann’smap of the cerebral cortex is widely used to denoteareas of the brain in functional imaging, electrophys-iology, and related clinical applications. In the mid-1900s, electrophysiological studies revealed that therepresentation of the basilar membrane was preservedin the primary auditory cortex (Ades and Felder, 1942;Licklider and Kryter, 1942; Bailey et al, 1943; Pribramet al, 1954; Hind et al, 1958; Katsuki et al, 1962; Grosset al, 1967; Celesia and Puletti, 1969). These studieswere followed by others in which the anatomical andphysiological features of this region were explored inmore detail, showing tonotopic organization of areas,subcortical inputs, and connections between fields(Nauta, 1957; van Buren and Yakovlev, 1959; Pandyaet al, 1969; Merzenich et al, 1973; Mesulam andPandya, 1973; Pandya and Sanides, 1973; Imig et al,1977). Studies of the auditory cortex of nonhumanprimates and humans since that time representstepwise refinements of previous findings, culminatingin a working model that is the subject of ongoingtesting and modification (Kaas and Hackett, 1998,2000; Hackett, 2003; Hackett, 2007a, 2007b).IDENTIFICATION OF AUDITORY AREAS INTHE BRAINIn the cerebral cortex of the brain, the term auditorycortex refers to areas that are the principal targetsof either the ventral (MGv) or dorsal (MGd) divisions ofthe medial geniculate complex (MGC) in the thalamus.By that definition, auditory cortex occupies a largeportion of the ventral (lower) bank of the lateral sulcus(LS) and superior temporal gyrus (STG) in humansand nonhuman primates (Fig. 1). In humans, theseareas encompass the transverse temporal gyri (TTG) ofHeschl (HG) and the planum temporale, roughlycorresponding to areas 41, 42, 52, and 22 of Brodmann(1909). Outside the boundaries of auditory cortex arenumerous areas of the brain that receive inputs fromauditory cortex, but few or no inputs from the MGv orMGd. These auditory-related areas are located else-where in the temporal, parietal, and frontal lobes, andtend to be sites of multisensory convergence, in whichthe processing of auditory, visual, and somatosensoryinputs occurs (Romanski et al, 1999; Kaas andHackett, 2000; Ghazanfar and Schroeder, 2006).The designation of an area as auditory or