Project 1

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PROJECT SUMMARY/ABSTRACT – PROJECT 1 We propose to leverage our state-of-the-art expertise in vivo optical imaging and data analysis, combined with behavioral training, electrophysiology, and modeling, to investigate fundamental aspects of the pial neurovascular circuit in mice. This circuit is composed of a fully connected albeit irregular lattice of pial arterioles that undergo rhythmic oscillations - in the ~ 0.1 Hz vasomotor band - in isolation. The pial circuit integrates neuronal activity from neighboring vessels, underlying neurons, and subcortical regions to produce dynamic patterns of coherent oscillations in arteriolar diameter across the cortical mantel. These patterns contain regions at slightly different frequencies, i.e., they parcellate, in a manner that partially reflects the underlying neuronal input. We seek to understand and model this parcellation, which is readily measured with optical and functional MR imaging, and quantify how it defines brain state. Aim 1 seeks to formulate an understanding of fundamental physiology of the pial neurovascular circuit. This includes testing if brain arterioles truly act as non-linear interacting oscillators, so that they entrain and phase lock rather than passively filter. In Aim 2 we explore the competitive conditions that break locking between oscillators so that parcellation can occur. These experiments gain from our ability to use sensory stimuli from different modalities - touch, vision and audition - each of which targets a different brain area. They also gain from our ability to drive subcortical inputs, particularly those involved in homeostatic brain function, and use direct optogenetic stimulation where needed. Lastly, these experiments gain from interaction with the neuromodulatory investigations of Project 2, as subcortical neuromodulation provides both regional and cortex-wide control of neuronal excitability. The experimental plan is motivated by the theory of phase-coupled oscillators that dates from Yoshiki Kuramoto's 1975 Lecture Notes. In this regard, progress on Aims 1 and 2 are strongly interwoven with the theory effort of Project 4. Aim 3 will connect the dynamics of the pial neurovascular circuit with the dynamics of the penetrating arterioles; these vessels source energy substrates to the parenchyma. These experiments, also in rodents, involve deep imaging of the cerebral mantel with CBV fMRI and adaptive optics two photon imaging. Together with direct measurements of oxygen transport in Project 2, these data provide input for calculations of oxygen tension throughout the cortical mantle. This, in turn, provides a means to couple BOLD fMRI and/or CBV fMRI to pial neurovascular dynamics. All told, the experimentation and analysis of Project 1 will provide a way forward to infer the state of the human mind from MR imaging (Project 3).