Project Summary Astrocytes are major constituents of neural circuits, comprising nearly one third of cells in gray matter. They interact with neural circuit elements both physically and functionally via bidirectional signaling with neurons. Astrocytes respond to neural activity in large part by increasing intracellular calcium on multiple spatial and temporal scales, via a variety of mechanisms. These calcium signals are a necessary component of the signaling pathway for many forms of astrocyte signaling back to neurons. Thus, an understanding of the functional role of astrocytes in neural circuit function requires a quantitative elucidation of the spatial and temporal neural activity patterns that elicit calcium signaling in astrocytes, and the integration of subcellular calcium signals within individual astrocytes. We propose to define these relationships by making use of the precise neural circuit organization in ferret visual cortex. Ferret visual cortex is functionally organized into precise orientation columns, such that different orientations of visual stimulation produce spatially distinct activity patterns in neural circuits, which enables precise experimental control of the spatial patterns of neural activity. We will specifically address 1) the subcellular compartmentalization of astrocyte responses to different stimulus orientations, 2) the subcellular organization of responses under precise control of stimulus amplitude and duration and 3) the impact of the different neural activity patterns underlying different brain states on astrocyte calcium responses. Together these studies will provide unprecedented quantitative insight into 1) the spatial patterns of neural activity that are required to activate astrocyte calcium signaling, 2) the temporal integration of the magnitude of neural activity that are necessary to activate astrocyte calcium signaling and 3) the brain states that promote astrocyte responses to neural activity. Quantitative definitions of these rules will provide an important baseline against which to compare and test the role of astrocytes in the brain dysfunction of pathological states related to diseases of mental health.