Project 2

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Abstract We propose to investigate the role of neuromodulation in the phenomenon of “whole-cortex” activity of the pial neurovascular circuit. This circuit is composed of a network of pial arterioles that integrate neuronal activity with the intrinsic arteriolar vasomotion producing dynamic patterns of coherent oscillations in the arteriolar diameter effectively parcellating the cortical mantle. Prior research suggests that ascending neuromodulatory systems may work in parallel affecting the brain state and processing capacity of large-scale cortical networks. In the majority of these studies, however, the presence of neuromodulatory neurotransmitters in the cortex was not directly measured. Rather, their release was inferred from stimulation of the corresponding subcortical nuclei or indirect measures. To overcome this limitation, in the proposed project we will use direct, selective and sensitive optical probes for acetylcholine, norepinephrine, dopamine and serotonin and track the presence of these neurotransmitters in space and time across the cortical mantle in awake behaving mice. We will combine these probes with optical imaging of neuronal Ca2+, blood oxygenation, optically transparent electrode arrays, optogenetic manipulations and BOLD fMRI. Using these tools, including those pioneered by the members of our team, we will address the role of neuromodulation in generation of (i) large-scale spontaneous cortical neuronal activity observed with wide-field Ca2+ imaging, (ii) temporally coherent patterns of vasomotion in the pial neurovascular circuit, and (iii) the resultant spatiotemporal pattern of hemodynamic fluctuations. Further, we ask whether these spatiotemporal patterns of vasomotion and hemodynamics, which can be measured noninvasively, can be used to infer the underlying internal brain state and/or activity of specific neuromodulatory systems. We will collaborate with Project 1 to understand the rules of integration of the neuromodulatory drive with local neuronal activity and intrinsic oscillatory dynamics within the pial neurovascular circuit. We will also collaborate with Project 3 to ensure that our findings translate up the scale from mice to humans. A critical link to Project 3 will be simultaneous optical/fMRI studies in awake mice. Finally, we will work with Project 4 to devise a phenomenological mathematical model that captures the essence of a brain state from the standpoint of the vascular integrator producing large-scale patterns of coherent vascular/hemodynamic fluctuations. This Project will provide a novel, unprecedented view on the role of neuromodulation in orchestrating large- scale spontaneous neuronal and hemodynamic activity, explore the underlying mechanisms, and offer a strong physiological foundation for the interpretation of large-scale fMRI signals and better understanding of the mechanisms linking spontaneous neuronal activity to cognitive performance. In collaboration with other Projects, we will deliver a predictive, conceptual model of local and global control of the pial neurovascular circuit and inference of brain states and specific neuromodulatory circuits in humans.