Despite advances in functional neural imaging, penetrating microelectrodes provide the most direct interface for the
extraction of neural signals from the nervous system and are a critical component of many high degree-of-freedom braincomputer
interface devices. Electrode insertion is a traumatic event that elicits a complex neuroinflammatory response.
In this investigation we applied optical coherence microscopy (OCM), particularly optical coherence angiography
(OCA), to characterize the immediate tissue response during microelectrode insertion. Microelectrodes of varying
dimension and footprint (one-, two-, and four-shank) were inserted into mouse motor cortex beneath a window after
craniotomy surgery. The microelectrodes were inserted in 3-4 steps at 15-20°, with approximately 250 μm linear
insertion distance for each step. Before insertion and between each step, OCM datasets were collected, including for
quantitative capillary velocimetry. A cohort of control animals without microelectrode insertion was also imaged over a
similar time period (2-3 hours). Mechanical tissue deformation was observed in all the experimental animals. The
quantitative angiography results varied across animals, and were not correlated with device dimensions. In some cases,
localized flow drop-out was observed in a small region surrounding the electrode, while in other instances a global
disruption in flow occurred, perhaps as a result of large vessel compression caused by mechanical pressure. OCM is a
tool that can be used in various neurophotonics applications, including quantification of the neuroinflammatory response
to penetrating electrode insertion.