tonotopie

Tonotopie, or tonotopy, is the spatial arrangement of neuronal responses to sound according to frequency. In the auditory system, neurons that prefer similar sound frequencies are located near each other, creating a tonotopic map from low to high frequencies.

In the cochlea, the basilar membrane is stiff at the base and flexible at the apex, so high frequencies peak stimulation at the base and low frequencies toward the apex. Hair cells at different locations transduce frequencies into neural signals that preserve this frequency gradient in the auditory nerve. As signals ascend, the tonotopic organization is maintained through pathways: cochlear nucleus, superior olivary complex, inferior colliculus, medial geniculate body, and the auditory cortex. Within each structure there can be multiple maps or overlapping representations, and some areas combine frequency with other features.

Tonotopy supports precise frequency discrimination and the processing of complex sounds such as speech. It is a fundamental principle used in the design of cochlear implants, which stimulate arrays in a tonotopically organized fashion. Pathologies such as hair cell loss and cochlear damage can degrade the map; some reorganization can occur following auditory deprivation, while training can induce plastic changes. Developmentally, tonotopy is established early and remains malleable to some degree in adulthood.