Spatial processing in the primate auditory cortex

Spatial localization of auditory stimuli is dependent on the cerebral cortex, yet it remains unclear how cortical activity gives rise to spatial percepts. It has recently been proposed that spatial information is processed serially within the primate auditory cortex, initially in the primary auditory cortex (AI) through the auditory areas caudal to AI, particularly the caudomedial (CM) and caudolateral fields, and onward to the parietal lobe. The activity of single neurons in AI and CM supports this hypothesis, where a greater percentage of CM neurons are sensitive to the spatial location of acoustic stimuli than AI neurons, and the spatial sensitivity of CM neurons extends across a broader range of the stimulus spectrum compared to AI neurons. Further, populations of CM neurons are better able to predict sound localization ability than are populations of AI neurons. We have recently explored the effects of stimulus intensity on both sound localization performance and the spatial sensitivity of auditory cortical neurons. The preliminary results of these experiments again indicate that spatial information is serially processed between AI and the caudal fields. The effects of visual stimulation on auditory localization have also been investigated. Under the appropriate circumstances, visual stimuli can "capture" the spatial location of auditory stimuli in both humans and monkeys. This perceptual illusion suggests that there is a plastic shift in auditory spatial perception. Where the representation of this shift resides is unknown, although two likely candidates are the multimodal regions of the parietal lobe and the superior temporal sulcus.