Chronic alteration of Ca ²⁺ and hemodynamic signals induced by intracortical microstimulation in the visual cortex of awake mice

Understanding the chronic effects of intracortical microstimulation (ICMS) and device implantation on cortical function is essential for the development of stable neuroprosthetics. We chronically implanted microelectrode into Thy1-GCaMP6s mice and conducted longitudinal mesoscopic widefield and two-photon Ca ^2#x002B; imaging alongside intrinsic optical signal recordings over 12 weeks. Six ICMS frequencies (10-500 Hz) and contralateral visual LED stimuli were delivered in repeated sessions. Oxygen extraction fraction (OEF) was estimated from dual-wavelength reflectance, and hemodynamic response functions (HRF) were derived via regularized deconvolution. Over the chronic period, 25-Hz ICMS evoked progressively larger Ca ²⁺ responses whose duration was extending, while spatial spread remained stable around 500 µm. Concurrently, OEF reductions deepened, reflecting increased relative blood supply, and the spatial extent of OEF signals contracted in the first week before expanding by day 21. After discharge-like Ca ²⁺ events emerged in nearly half of mice, predominantly under 25-Hz ICMS. HRF peak amplitude increased between day 0 and days 7-21, with latency decreasing. Chronic ICMS induces progressive potentiation of neuronal and vascular responses alongside local neurovascular uncoupling on day 0 and sustained silencing of spontaneous activity near the implant. These dynamics exhibiting a stabilization 6-7 weeks after the implantation, coupled with frequency-dependent after discharges, underscore the need for adaptive stimulation strategies prior to the stabilization and to prevent the after discharge and implant designs that mitigate local suppression and ensure long-term stability of cortical neuroprostheses.