Spatiotemporally distinctive astrocytic and neuronal responses to repetitive intracortical microstimulation

Objective
Astrocytes are increasingly recognized as active modulators of neuronal synaptic transmission. Intracortical microstimulation (ICMS) is widely used to manipulate neuronal activity, yet the accompanying astrocytic responses remain poorly characterized. This study aims to systematically characterize and compare astrocytic and neuronal spatiotemporal dynamics evoked by ICMS. 

Approach
We combined ICMS with dual-color in vivo two photon calcium imaging in mouse visual cortex to simultaneously measure neuronal and astrocytic activity and analyzed their spatial recruitment and temporal dynamics. 

Main results
Astrocytes were robustly recruited by ICMS at currents as low as 10 μA, comparable to neuronal activation thresholds. Unlike neurons, astrocytic responses exhibited weaker spatial dependence on electrode proximity and greater temporal variability across trials. At higher stimulation intensities (>=50 μA), astrocytic response magnitude and responsiveness (i.e., response peak amplitude, number of responsive trials), attenuated across repeated trials and fell below the detection threshold. Neuronal responses decreased in magnitude across trials as well but remained reliably above activation threshold. Despite these distinctions, astrocytic activation was correlated with neuronal activity: regions with active astrocytes exhibited higher neuronal response magnitudes, while astrocytic responses were strongest in regions lacking neuronal somata, potentially indicating preferential activity at neuronal processes. 

Significance
These results establish astrocytes as an active and distinct component of ICMS-evoked cortical dynamics, whose activity is coupled to neuronal responses yet exhibits spatial specificity, highlighting the importance of incorporating glial signaling into the interpretation and optimization of neurostimulation and neuroprosthetic strategies. 
 
&#xD.