Tonotopic mapping

Tonotopic maps are found in the cochlear nuclei, advanced olivary nucleus, inferior colliculus, and auditory cortex. A few structures have several maps. The cochlear nucleus is subdivided into iso-frequency strips, each having cells with alike characteristic fre-quencies (CFs). Strips representing increasingly higher frequencies are found progressively more posteriorly. In the primary auditory cortex, iso-frequency columns running via the whole thickness of the cortex are arranged in isofrequency strips running mediolaterally, with low frequencies stands for rostrally and high frequencies caudally as shown in figure below. There are at least three other tonotopic maps in the auditory cortex. Adjoining maps are always mirror images of each other. In humans beings there is no great over-representation of particular frequencies.

                                         Figure: Tonotopic map of the human primary auditory cortex.

Some regions of auditory cortex, for example, secondary auditory cortex (AII), are less fine tonotopically organized and contain cells that respond to a wider range of frequencies.