Transverse temporal gyri

At a glance

English

Transverse temporal gyri

Latin (TA2)

Gyri temporales transversi

System

Brain and spinal cord

Region

Head

Side

Paired, left and right

About the transverse temporal gyri

The transverse temporal gyri, often called Heschl's gyri after the Austrian anatomist Richard Heschl, are found only when the lateral (Sylvian) sulcus is opened. They lie on the upper face of the superior temporal gyrus, the part that forms the floor of the sulcus, and they run obliquely from the outer surface inwards towards the insula. That inward, mediolateral course sets them apart from the other temporal gyri, which all run from front to back.

There may be one gyrus or two, and the number varies between people and between the two hemispheres without following handedness or language dominance. In a sagittal MRI slice a single gyrus looks like an omega, while two gyri split by a sulcus make a heart shape. Behind them, across Heschl's sulcus, lies the flat triangle of the planum temporale, which is usually larger on the left and belongs to the wider speech area around Wernicke's region.

Functionally the gyri hold the primary auditory cortex, Brodmann areas 41 and 42. They are the first cortical stop for sound: fibres from the medial geniculate body of the thalamus reach them through the auditory radiation in the sublenticular part of the internal capsule. The cortex is tonotopic, with low and high pitches mapped along the length of the gyrus. From here signals go on to the surrounding belt of auditory association cortex. Imaging studies link the left side with fast changes in sound, useful for speech, and the right side with slower changes such as pitch; people who learn tone languages easily tend to have larger gyri. The area is also active during spontaneous inner speech and helps generate the mismatch response to an unexpected sound.

Because each ear projects to both hemispheres, damage to one transverse temporal gyrus does not cause deafness in one ear; it tends instead to impair locating sounds and separating them. Damage to both sides can produce cortical deafness. Irritation of the area by a seizure focus can cause simple auditory hallucinations such as buzzing or ringing.

Function and supply

Function

Primary auditory cortex: the first cortical area to receive and analyse sound, mapped by pitch.

Blood supply

Branches of the middle cerebral artery running in the lateral sulcus, chiefly its temporal branches.