Auditory experience can reshape cortical maps and transform receptive field properties of neurons in the auditory cortex of the adult animal. The exact form of this plasticity depends on the behavioral context, and the spectrotemporal features of the salient acoustic stimuli. This has been shown by combined physiological and behavioral approaches in our previous experiments in which "on-line" spectrotemporal receptive fields (STRFs) were rapidly and comprehensively characterized simultaneous with the animal behavior. The experiments also contrasted STRF plasticity in single cells across different auditory tasks employing various acoustic signals with controlled spectral and temporal features. These results are consistent with findings of adaptive plasticity in the motor and other sensory systems and support the hypothesis that auditory cortical cells may undergo rapid, context-dependent changes of their receptive field properties when an animal is engaged in different auditory behavioral tasks. This kind of plasticity would likely involve a selective functional reshaping of the underlying cortical circuitry to sculpt the most effective receptive fild for accomplishing the current auditory task. What are the underlying mechanisms that give rise to this extraordinary functional plasticity? The goals of the proposed research are to extend our studies of task-related plasticity in A1 to a variety of new tasks involving speech stimuli, new behavioral paradigms (contrasting discrimination versus recognition), to explore plasticity in the higher order auditory cortical fields of the PEG and surrounding areas, and finally to investigate the possible role of top-down signals from frontal cortex in modulating adaptive plasticity in the auditory cortex. We propose to rigorously test the hypothesis that frontal cortical neurons encode task rules, expectancies, goals and the task-related meaning of acoustic stimuli, and further, that when an animal performs different auditory tasks, top-down influences from frontal areas contribute to the induction of rapid adaptive plasticity in auditory cortex, that reflects boh the nature of the stimuli and goals of the tasks. We shall also conduct our physiological experiments with arrays of planar and laminar microelectrode arrays Our preliminary studies from simultaneous neuronal recordings of single units and local field potentials in auditory and frontal cortex have already lead to exciting new insights, that may lead to progress in understanding the interactions within an extended neuronal network that give rise to adaptive plasticity.
The phenomenon of plasticity that is the focus of the proposed research is fundamental to learning, behavioral performance, and to the repair of the nervous system after damage. Our goal is to understand how plasticity manifests itself in the responses of the auditory cortex, and how do the acoustic stimuli interact with the behavioral feedback to influence the changes in the cortex. The findings of this research could have profound consequences for the design and deployment of hearing aids and cochlear implants.
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