Integration of microprism and microelectrode arrays enables simultaneous electrophysiology and two-photon imaging across all cortical layers

Abstract

Implantable microelectrode arrays (MEAs) have been widely used for multisite neural recording and stimulation in basic neurophysiological research and brain-computer interface (BCI) applications. However, exactly how neural electrodes interact with brain cells remains poorly understood. Two-photon microscopy (TPM) is a valuable tool to observe cellular activities in vivo, but the imaging depth is usually limited to the superficial brain regions. In this work, we build a multi-functional device by integrating a microprism with a custom-designed transparent MEA, allowing long-term sub-cellular imaging, electrophysiological recording, and microstimulation in the same region across all cortical layers. The accessible depth is about six times deeper than the conventional method (~1000 μm vs. ~150 μm). By implanting this device in Thy1-GCaMP6s mice, we obtained stable TPM images of neuronal calcium activities across multiple cortical layers near the MEA, as well as single-unit recordings for 16 weeks. For the first time, we visualized the neuronal network activation pattern of all cortical layers in response to electrical stimulation with TPM, demonstrating the influence of stimulation location, amplitude, and frequency on neuronal activity. This novel MEA-on-microprism design provides a powerful multimodal method to investigate electrophysiology and cellular activities throughout all cortical layers in living animals.