Visual and Auditory Processing Streams in the Cerebral Cortex

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Vision has long served as a model system in health and disease for the analysis of perceptual and cognitive systems at the level of the cerebral cortex. Great progress has also been made in recent years regarding an understanding of higher cortical areas involved in auditory cognition. However, knowledge about auditory processing streams still lags far behind that in vision. We propose to use single- and multi-unit electro- physiology to study cortical areas along the superior temporal gyrus (STG) and sulcus (STS) in a nonhuman primate, the rhesus macaque, whose cortical organization is similar to that of humans. Our analysis is based on the hypothesis that at least two specialized processing streams exist both in the visual and auditory system, an antero-ventral stream for the identification of objects, and a postero-dorsal stream for the analysis of space. Thus we predict that anterior superior temporal areas (AST) rostral and lateral to primary auditory cortex (A1) show enhanced selectivity for auditory objects regardless of spatial location (Specific Aim 1), whereas posterior superior temporal areas (PST) caudal to A1 show enhanced selectivity for location in space regardless of auditory object type (Specific Aim 2). We will focus on the processing of species- specific communication calls and will test whether neurons in the superior temporal (ST) cortex can form invariances for pitch and caller identity. In a third Specific Aim, we will use anatomicaltracers, injected into physiologically characterized regions, to uncover the input connections to AST and PST from auditory, visual, and multisensory areas. Our studies, using alert monkeys trained in a behavioral task, will contribute to the understanding of unified principles of perception and cognition across sensory systems. They will further our understanding of deficits in human cognition from stroke or Alzheimer's disease, which result in visual and auditory agnosia as well as loss of spatial orientation. The studies are also relevant for disorders such as dyslexia and autism, which include problems in reading comprehension or a person's ability for social communication. Auditory processing deficits are a common symptom in both, and clarification of the neural mechanisms for auditory cortical communication is a major prerequisite for finding a cure. Finally, understanding temporal cortex with its massive connections to frontal cortex will yield important clues about higher mental disorders, such as schizophrenia, which are often characterized by auditory hallucinations.