In recent years, great progress has been made in understanding cortical areas involved in auditory perception and cognition. Work from our laboratory as well as many others has demonstrated the existence of functionally specialized processing streams in both humans and nonhuman animals (see Rauschecker, 2012, for review). A ventral "what"-stream was shown to be involved in the identification of complex sounds;a dorsal "where"- stream was defined as specialized in processing space and motion. Work in the previous funding period has concentrated on understanding processing principles in the ventral stream and has produced numerous results (see Progress Report). Work in the upcoming funding cycle will focus on the dorsal stream. In particular, we propose to study auditory areas within posterior superior temporal cortex (pST) and auditory-related areas in parietal and premotor cortex of awake rhesus monkeys. Building on prior results, we predict that areas of the dorsal stream in pST and parietal cortex are particularly selective for spatial location. In addition, a new, expanded role for dorsal-stream function in audio-motor control and integration has been proposed (Rauschecker, 2011). We will test this hypothesis by training monkeys to produce sound sequences on a special-built behavioral apparatus ("monkey piano"). These sequences as well as untrained control sequences will then be used as auditory stimuli in functional magnetic resonance imaging (fMRI) studies and single-/multi- unit recordings from the same monkeys. The study is divided into three specific aims:
Aim 1 will investigate tuning for spatial and temporal properties in areas of the caudal belt and parabelt (CB/CPB) using fMRI and single-/multi-unit recording. Specialization for motion-in-space will be tested by presenting stimuli mimicking looming objects.
Aims 2 and 3 will study the newly proposed role of the dorsal stream in audio-motor control and integration:
Aim 2 will utilize fMRI in combination with behavioral training;
Aim 3 will use parallel recording from multiple sites with multi-electrode arrays (MEAs). By testing how features relevant to spatial and audio- motor functions are represented relative to each other in dorsal-stream areas, we will determine whether these functions are accomplished relatively independently in two branches of the stream, or whether they are combined into one integrated audio-spatio-motor processing pathway. Our studies, using alert monkeys trained in a behavioral task, will contribute to the understanding of unified principles of cortical function across sensory systems. They will further our understanding of deficits in human perception and 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 language comprehension or ability for social communication. Finally, understanding temporal and parietal networks with their massive connections to frontal cortex will yield important clues about higher neurological and mental dysfunctions, such as attention-deficit disorder and schizophrenia.
The cerebral cortex is the neural basis of conscious perception and cognition. While visual cortex has been the major model system for half a century, understanding of common processing principles of vision and audition will lead to a more generalized description of cortical function. The primary goal of our research is, therefore, to better understand the neural circuitry of cortical brain structures using auditory cortex as a model system. Our studies will help to develop more adequate treatment and rehabilitation of higher-order neurological and mental disorders, such as agnosia, dyslexia, autism and schizophrenia.
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