Selective attention adapts sensory processing to the immediate goals of an observer by enhancing the neural representation of task relevant stimuli at the expense of irrelevant stimuli. Prior studies in both humans and monkeys show that attention modulates neuronal responses at every stage of visual processing after the retina. While auditory selective attention has been extensively studied in humans the topic is almost untouched by studies in monkeys. The broad goal of this R21 proposal is to initiate studies of the neural mechanisms of selective attention by direct electrophysiological recording in primary auditory cortex (A1) of the monkey. Accumulating evidence indicates that neuronal oscillations reflect organized rhythmic shifting of excitability in neuronal ensembles on different spatial and temporal scales, and that these oscillations are fundamental components of normal brain function with a crucial role in sensory, cognitive and motor operations. In particular, recent studies in visual cortex reveal that the structure of ongoing oscillatory activity can adapt or """"""""entrain"""""""" to the temporal (rhythmic) structure of an attended sensory stimulus stream. Entrainment aligns the high excitability phase of neuronal oscillations with the timing of events in the attended stream, thus amplifying their neuronal representation. As rhythmic structure is essential to many biologically significant acoustic stimuli (e.g., speech sounds), oscillatory entrainment would appear particularly useful as a mechanism of attentional selection in the auditory system. This proposition has strong psychophysical support, but has not been directly tested at a neurophysiological level. We will evaluate the overall hypothesis that the entrainment of neuronal oscillations to the temporal structure of an attended acoustic stream results in enhanced neuronal responses to events that comprise that stream, and suppressed neuronal responses to stimuli that deviate from it along the two fundamental organizing dimensions of auditory processing, time (rhythm) and frequency. Behavioral measures, along with laminar current source density and multiunit activity profiles sampled in A1 during task performance will address the specific aims of defining the effects of 1) attended rhythm, and 2) attended tone frequency on auditory processing. Since attentional entrainment of neuronal oscillations appears critical to efficient, adaptive behavior in a complex environment, its disruption would likely result in cognitive impairment. Defining the neural underpinnings of attention entrainment is a crucial step in understanding the mechanisms of cognitive function and dysfunction.
Attention entrainment of neuronal oscillations is believed to be crucial to the effective use of ongoing physiological processes in adaptive processing of complex natural stimuli, yet the rules that govern it and its function are still largely unknown. We propose to explore oscillatory entrainment as a mechanism of auditory selective attention. Since deficits of auditory processing are key symptoms in numerous neuropsychiatric disorders, our findings will have important implications for improved understanding and treatment of these disorders, and for advancing our understanding of dynamic brain operations in general.
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