Heschl's gyrus
Gyri temporales transversi (Heschli)
cortical
The transverse temporal gyrus running medial-to-lateral on the dorsal surface of the superior temporal gyrus, deep within the lateral fissure. Heschl's gyrus is the cortical termination of the central auditory pathway from medial geniculate nucleus to primary auditory cortex (A1). Its number is anatomically variable: most individuals show one full gyrus on each hemisphere, but two or three transverse gyri are well-documented in normal brains and intersubject variability is among the largest of any primary sensory area.
The medial two-thirds of Heschl's gyrus correspond to Brodmann area 41 (primary auditory cortex, A1), with the highly granular koniocortex characteristic of primary sensory areas. The lateral portion and the surrounding superior temporal cortex carry BA 42 (the first belt of higher-order auditory processing). A1 is tonotopically organised, with a roughly anteromedial-to-posterolateral gradient from high to low frequencies, mirroring the cochlear apex-to-base arrangement preserved through the auditory brainstem.
The planum temporale immediately posterior to Heschl's gyrus is a key node in the dorsal language stream and is consistently larger in the left hemisphere than the right, an asymmetry first quantified by Geschwind and Levitsky in 1968 and proposed as a structural correlate of language lateralisation.
Heschl’s gyrus is named for Richard Heschl, the Vienna anatomist who described it in 1878. Its position deep within the lateral fissure means it is rarely visible on lateral views of the unprepared brain; in textbook illustrations it is usually shown after retraction or removal of the overlying frontoparietal operculum, or in axial or coronal sections through the lateral fissure.
The handedness of Heschl’s-gyrus asymmetry has been a fruitful question in the structural neuroanatomy of language. The planum-temporale asymmetry is reliable across most right-handed individuals, but the relationship between this asymmetry and behavioural language lateralisation is statistical rather than deterministic; many strongly left-lateralised speakers show right-greater planum temporale on imaging, and vice versa. The asymmetry is detectable in foetal brains by the third trimester, suggesting a developmental rather than experience-driven origin.
Patients with auditory hallucinations in psychosis show altered activation patterns in Heschl’s gyrus and adjacent superior temporal cortex, and chronic schizophrenia is associated with reductions in left superior temporal grey-matter volume that include Heschl’s gyrus.