For echolocation, the mustached bat Pteronotus parnellii emits complex orientation sounds and listens to echoes. We have demonstrated that certain types of biosonar information are extracted by neurons examining different combinations of signal elements and are systematically represented in separate areas of the auditory cortex. We now want to explore how other types of biosonar information are represented in other areas, how biosonar information flows through these areas, whether the brain has areas for integration of the different types of biosonar information to recognize an overall target image and how high is the upper limit in specialization (complexity of response properties) of single neurons. To explore these important problems in neural mechanisms for processing complex acoustic signals, we will combine electrophysiology with """"""""tracer anatomy"""""""". We will examine response properties of single neurons in the individual areas and inject radioactive amino acids or horseradish peroxidase or fluorescent dyes into the recording sites to identify the destination or origin of auditory information through these areas. We will then insert microelectrodes into """"""""target areas"""""""" to study response properties of single neurons and functional organization (spatial distribution of response properties of single neurons) of the target areas. Tracers are injected into the target areas for further exploration of the information flow. The auditory system of the mustached bat is specialized for processing biosonar information for echolocation (communication with environment). The left cerebral hemisphere of a man contains Wernicke's area which is specialized for processing speech. A thorough understanding of the specialization in speech processing will not be obtained without direct physiological studies on the Wernicke's area. However, the insight to it will be obtained from research on animals specialized for processing complex acoustic signals, as recently demonstrated. The acoustic signals used by the mustached bat are high in frequency but share basic acoustic patterns with those used by many other species of mammals, including man. Our proposed research is to explore neural mechanisms for processing complex acoustic signals in the bat, but it will significantly contribute to an understanding of the basic mechanisms for processing speech sounds.
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