One puzzling question in auditory neuroscience is how neurons in the cerebral cortex code acoustic space. An apparent paradox exists, where lesions of the auditory cortex result in profound sound localization deficits, but the spatial selectivity of most cells in auditory cortex are an order of magnitude greater than psychophysically measured localization acuity. Preliminary experiments in human subjects in my laboratory show that subjects make absolute judgements of acoustic space in a range of 10- 50 degrees, suggesting that the spatial tuning of auditory cortical neurons may more accurately reflect the perception of stimuli in absolute space than previously thought. To date, there have been no combined psychophysical and neurophysiological studies in animals performing a psychophysical task that measures sound localization acuity. The experiments of this proposal will initiate this class of studies by recording the neuronal responses of single auditory cortical neurons in macaque monkeys while they perform a sound localization task. These studies will advance our understanding of cortical processing in the auditory system, and provide important insights into brain function that could have implications for rehabilitation therapies in the recovery from brain injury and stroke. Insights into the computational processes of auditory cortical neurons in the realm of localization could also lead to a better understanding of other computational processes of the auditory system, for example temporal processing, which is implicated in learning disabilities and speech perception.
SPECIFIC AIM 1 : To determine the ability of macaque monkeys to make saccadic eye movements to acoustic targets as a function of the stimulus frequency, bandwidth and spatial location in both azimuth and elevation. Macaque monkeys will be required to make saccadic eye movements to invisible acoustic targets that vary in frequency, bandwidth, and spatial location in azimuth and elevation. Eye position records will be used to accurately measure the magnitude and direction of localization errors. This information is essential to develop the macaque monkey as an animal model in future neurophysiological and neuroanatomical studies. These experiments will provide an extensive description of sound localization ability in this species and fill this important gap necessary for future studies of the neuronal mechanisms of auditory perception and behavior.
SPECIFIC AIM 2 : To determine the response properties of single neurons across a large extent of AI while monkeys perform a sound localization task, and to define how neuronal responses are altered as a function of the bandwidth, absolute spatial location, and perceived spatial location of the stimulus. The responses of single neurons in AI will be compared to the simultaneously measured localization acuity in these same monkeys. These data will provide important insights into how single neurons, and the population of neurons across AI, can potentially code acoustic space in a primate.
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