BEHAVIOR-DEPENDENT CLUSTERING OF ASTROCYTIC CA<SUP>2+</SUP> ACTIVITY IN POSTERIOR PARIETAL CORTEX OF AWAKE MICE

Astrocytic Ca²⁺ activity is considered, at least partly, an indicator of neuron–glia interactions, yet how astrocytes encode the behavior at subcellular level remains unknown. Especially, whether behavioral modulation affects the spatial organization of astrocytic Ca²⁺ events is unclear.
We imaged Ca²⁺ activity of astrocytes with two-photon microscopy on a single and multicellular level at high spatio-temporal resolution (1 um and 100 ms) in the posterior parietal cortex. Head-fixed animals were allowed to engage in spontaneous behaviors and were presented with auditory tones. To detect Ca²⁺ activities occurring at spatially arbitrary locations, we used GCaMP8f tagged to the plasma membrane which is expressed after AAV5.GfaABC1D.CI.lck-jGCaMP8f.SV40 injection. Ca²⁺ events were identified using an automated, event-based detection framework (AQuA2).
Behavior onset–aligned analyses revealed that individual Ca²⁺ event properties, including ΔF/F₀ peak amplitude, duration, rise/decay times, and spatial size, were preserved across behaviors. In contrast, Ca²⁺ events clustered at the behavior onset. This effect was observed even by subtle facial movements that have been largely overlooked in previous studies. In addition, event occurrence increased transiently following behavior onset. Tone presentations did not cause this effect in posterior parietal cortex.
These results indicate that astrocytes encode behaviors predominantly through a reorganization of the timing and spatial patterning of Ca²⁺ events in subcellular level, rather than through changes in Ca²⁺ dynamics that had been examined before, such as peak ΔF/F₀ amplitude and duration. This spatial modulation may provide a flexible mechanism for astrocytes to reflect ongoing circuit activity over multiple levels of behavior.