Microglia surveillance during sustained intracortical microstimulation at the electrode-tissue interface

• Ten-hertz ICMS increased microglial process motility without classical morphological activation; microglial extensions dynamically tracked neurons showing early activation or subsequent activity.¹
• In vivo two-photon imaging in Cx3cr1-GFP/jRGECO1a mice tracked microglial motility, morphology, and process orientation relative to electrode placement and neuronal calcium (ΔF/F) over the first three days post-implantation.¹
• Findings inform long-term efficacy and biocompatibility of neuroprostheses and stimulation protocols (Journal of Neural Engineering).¹
• Stimulation protocol: symmetric cathodic-leading biphasic pulses at 10 Hz, 200 µs pulse width, delivered for 1 hour via a single-shank microelectrode implanted in L2/3 of visual cortex; designed to model low-frequency therapeutic ICMS parameters used in sensory neuroprostheses.¹
• Microglial process orientation to activated neurons was highly dynamic: by post-implantation Day 2, extensions were significantly biased toward neurons whose ΔF/F exceeded a 3 SD threshold post-stimulation (mean angle 74.26° ± 11.83°), but this orientation reversed away from those same neurons after 40 continuous minutes of stimulation (116.99° ± 9.19°; p = 0.001732) — suggesting an active homeostatic withdrawal response to sustained calcium elevations.¹
• Microglial contact frequency correlated with neuronal adaptation profiles: neurons that became depressed post-implant received the most microglial contacts immediately (1.15 ± 0.3 contacts; p = 0.046), implicating microglia as active participants in modulating early cortical circuit adaptation.¹
• Multi-day electrode implantation alone (without stimulation) accelerated overall microglial motility and polarization toward the device, but 10 Hz ICMS alone did not alter microglial branching or soma morphology — a key distinction from classically activated (amoeboid) microglia typically associated with inflammatory injury responses.¹
• The study is described by the authors’ lab (B.I.O.N.I.C. Lab, Kozai group) as the first direct demonstration that microglial surveillance dynamics during sustained ICMS are directed toward activated neurons, reframing microglia as active homeostatic regulators rather than passive inflammatory responders during electrical stimulation.²
• Broader significance: long-term ICMS efficacy in sensory BCIs (e.g., Neuralink’s N1, cortical prostheses for touch feedback) is limited by foreign body response and biofouling; understanding that microglia track neural activity rather than simply reacting to electrode presence opens avenues for stimulation parameter optimization to promote anti-inflammatory microglial phenotypes and extend device longevity.²

Footnotes

1. https://iopscience.iop.org/article/10.1088/1741-2552/ae4652 ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

2. https://pubmed.ncbi.nlm.nih.gov/40661573/ ↩ ↩²