Organization and experience-dependence of auditory coding in forebrain

University Of California, San Francisco, San Francisco CA

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Abstract

DESCRIPTION (provided by applicant): Processing and perception of communication sounds such as speech are enormously important to humans, and hearing is a critical component of both. Yet we know surprisingly little about how the brain transforms auditory signals to accomplish these complex tasks. Our long-term objective is to further the development of a unified framework for understanding high-level auditory processing and how it changes, for good or ill, with experience and learning. To this end, we propose to study a stage in a central auditory circuit where there is a remarkable change from simple, primary-like response properties to complex vocalization-sensitivity, in the auditory forebrain of songbirds. These animals provide an excellent model for extracting general principles of higher-level sound processing, because they learn auditory tasks of similar difficulty to humans, and possess a hierarchical network of auditory areas that sub serve these tasks, including the avian equivalent of primary auditory cortex, field L, and several secondary areas that are the likely equivalent of belt cortex. Moreover, we have access to a rich set of auditory stimuli of behavioral relevance, songs. We recently found that within field L there is a strikingly orderly organization of receptiv fields, along spectral and temporal axes. We will ask whether and how this organization propagates to the next level, by mapping the response selectivity of these secondary areas to batteries of songs, using an information theory-based technique called maximally informative dimensions (MID). We will also record responses to songs learned earlier (from father, mate) to examine the additional hypothesis that sound memories learned early in life have a special representation in such areas. In parallel, we will test the anatomical and physiological contribution of the inputs from field L to these secondary areas, by selectively labeling or turnin off subsets of these inputs. Finally, armed with the knowledge of these circuits' organization, we will ask whether and how their receptive field organization and song representations change after birds learn a behavioral discrimination task that strongly focuses their attention on either spectral or temporal aspects of song, two key parameters mapped in field L, and critical both in normal and impaired auditory processing.