Network mechanisms for state-dependent consolidation of visual system plasticity

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Abstract: The long-term goal of this project is to identify thalamocortical network mechanisms involved in consolidating experience-dependent plasticity in the visual system. Sleep has beneficial effects for processes dependent upon synaptic plasticity, such as memory consolidation. Recent studies have shown that cortical areas engaged by waking sensory experience are "reactivated" during subsequent slow wave sleep (SWS), with local changes in electroencephalogram (EEG) oscillatory activity. Because these EEG oscillations are generated by rhythmic, synchronous firing of thalamic and cortical neurons, one untested hypothesis is that SWS thalamocortical activity leads to potentiation or depression of synaptic targets. Orientation-specific response potentiation (OSRP) in the mouse visual system involves potentiation of neuronal responses to visual stimuli of a specific orientation. OSRP is initiated by brief exposure to an oriented grating stimulus, and is consolidated "offline" in the hours immediately following visual experience. My preliminary data suggest that thalamocortical spindle (7-14 Hz) activity during SWS may play a critical role in OSRP consolidation. In the mentored phase of the proposed award (Aim 1), I will: (a) test whether SWS and SWS spindle oscillations are required for OSRP, and (b) assess whether during consolidation, SWS spindles 1) activate thalamocortical connections in a non-specific manner, or 2) mediate "reactivation" of thalamocortical connections in a manner consistent with prior visual experience. I will do this by recording ongoing activity and visual response properties in populations of neurons in the visual cortex and lateral geniculate nucleus of freely-behaving mice during baseline, waking visual experience, and a subsequent consolidation period of either: ad lib sleep, total sleep deprivation, rapid eye movement sleep (REM) deprivation, or selective interruption of SWS spindles. These studies will build upon the my prior research experience with multielectrode recording and data analysis, under the co-mentorship of Drs. Marcos Frank (my current postdoctoral advisor and an expert in the areas of sleep and visual cortex plasticity) and Diego Contreras (an expert in the areas of state-dependent thalamocortical network properties and network mechanisms involved in vision). During the mentored phase of the award, I will also develop expertise in using optogenetic techniques in combination with multielectrode recording in freely-behaving mice, in preparation for experiments outlined in Aim 2. In the independent phase of the award (Aim 2), I will use this combination of state of the art techniques to silence defined populations of thalamocortical, reticular thalamic, or corticothalamic neurons during particular states (wake, REM, or SWS), to test the necessity of thalamocortical activity within each state for OSRP consolidation. I hypothesize that generation and coordination of spindles by these neuronal populations during SWS is critical for this process. Together, these studies will reveal state-dependent network mechanisms necessary for consolidating plasticity following visual experience.