According to our anatomy-based working model, the primate auditory cortex consists of three major regions (core, belt, and parabelt) arranged in a processing hierarchy. It has been proposed that the rostral and caudal parts of those regions contribute to different functional streams, with the rostral parts coding mostly the identity of sounds, and the caudal parts spatial location. To test this hypothesis, the neuronal responses to interaural time differences (ITD) will be assessed for the core and the belt region of the macaque auditory cortex. First, it will be tested whether the three subdivisions of the core region (A1, R, and RT) have similar ITD response properties. The thalamic inputs from the ventral medial geniculate body (MGBv, lemniscal pathway) suggests that most neurons in the core region have sharply tuned ITD functions with a range of best ITDs and a preference for contralateral space. Any systematic variation amongst those subdivisions would suggest differences in their cortical and callosal connections, and therefore suggest parallel functional streams. The belt region receives thalamic inputs from the dorsal part of the MGB (extra-lemniscal). Hence, the hypothesis, that ITD coding is likely to be different between core and belt, will be tested.
