The Neural Basis of Audiovisual Temporal Processing and Perception: From Cortical Networks to Cellular Mechanisms

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In providing us with a more complete sensory experience, our brains naturally merge information from our different senses. In situations when an auditory and visual stimulus occur within ~100 ms of each other, we often perceive that they happened at the same moment, even though they were actually offset in time. Although this integration of closely-timed audiovisual stimuli can offer certain behavioural advantages, such as improved detection, identification and localization of objects in the environment, an overly broad window of temporal integration can be problematic, as information from truly separate events may not be correctly perceived as such. Recent human studies have suggested that the precision of perceptual binding of audiovisual stimuli is regulated by neural oscillations, especially in the gamma-band (>30 Hz), within the audiovisual cortex; a phenomenon that has been suggested to depend on local GABAergic neurotransmission. At present, however, the specific brain circuits and cellular mechanisms that regulate the putative oscillatory activity subserving audiovisual perceptual binding remain elusive, in part because the field has lacked suitable animal models for invasive studies. Toward that goal, my lab has recently established that rats represent an excellent model to study the neural basis of audiovisual temporal processing at the level of single neurons, local microcircuits and sensory perception. For example, using pharmacological manipulations, we revealed that GABAergic neurotransmission in the rat audiovisual cortex (V2L) not only controls the precise timing of audiovisual integration, but it also affects the window of time over which perceptual binding occurs. That said, given the complexity of the local GABAergic microcircuits and the various GABA-A receptor subunits expressed at specific locations on cortical pyramidal neurons, additional work is needed to uncover the cellular mechanisms by which GABAergic neurotransmission controls the temporal integration of audiovisual stimuli into a unified percept. In this proposal, we will use an advanced approach combining optogenetics/shRNA manipulation + in vivo electrophysiological recordings in behaving rats to address the following objectives: (1) To identify how unisensory vs. multisensory thalamocortical projections to the V2L cortex contribute to audiovisual temporal processing and perception; (2) To investigate the role of GABAergic interneurons within the V2L cortex on audiovisual temporal processing and perception, and; (3) To determine which of the specific GABA-A receptor subunits expressed on pyramidal neurons in V2L cortex are responsible for fine-tune audiovisual temporal processing and perception. Ultimately, given my lab's expertise, infrastructure and recent progress, no other lab in the world is as well-positioned to tackle the long-standing question: How does the mammalian brain integrate closely-timed auditory and visual stimuli into a unified percept?