primary auditory cortex

Meaning: The primary auditory cortex sits in the superior part of the temporal lobe, in Heschl's gyrus. It is the first cortical stop for hearing. Sound is transduced by hair cells in the cochlea, travels via the auditory nerve to the brainstem (including the superior olive and inferior colliculus), then to the medial geniculate nucleus of the thalamus, and finally to this cortex. Neurons here are arranged tonotopically, meaning neighboring locations respond to neighboring frequencies, mirroring the cochlea's frequency map. Input from both ears reaches each hemisphere, because auditory pathways cross and also stay on the same side at several points.

On the MCAT: Expect questions on the pathway order (cochlea → brainstem → medial geniculate nucleus → temporal lobe), on matching senses to thalamic relays (vision to the lateral geniculate nucleus, hearing to the medial geniculate nucleus, and most other senses to the ventral posterior nuclei), or on predicting deficits. Damage to one primary auditory cortex typically does not cause total deafness in either ear, since each ear projects to both hemispheres. Association areas nearby, such as Wernicke's area, handle meaning of speech.

Common confusion: Students equate the primary auditory cortex with Wernicke's area, or assume it understands language. It mainly processes basic features such as pitch and loudness. Higher-order interpretation, including speech comprehension, depends on the surrounding auditory association areas. Also, smell is the sense that bypasses the thalamus relay, not hearing.