Auditory cortex in the marsupial possum Trichosurus vulpecula.

A microelectrode mapping survey was made of the auditory cortex of the acallosal marsupial possum Trichosurus vulpecula. Single unit and unit cluster responses, as well as evoked potentials, were obtained from 64 tangential, cortical penetrations. Pontamine sky-blue marking of successful tracks aided in later reconstruction of tracks and identification of recording locations. Only one auditory field was identified. The 98 units sampled in this field covered a wide range of best frequencies from 330 Hz to 39 kHz with the most sensitive units (thresholds of best frequency of less than 10 dB SPL) being in the 17-19 kHz range. An orderly representation of cochlear place was found in the cortex with high frequencies located dorsally and low frequencies more ventrally. This orientation of frequencies is unlike that seen in other mammals.