Validation of transparent and flexible neural implants for simultaneous electrophysiology, functional imaging, and optogenetics

The combination of electrophysiology and neuroimaging methods allows the simultaneous measurement of electrical activity signals with calcium dynamics from single neurons to neuronal networks across distinct brain regions in vivo. While traditional electrophysiological techniques are limited by photo-induced artefacts and optical occlusion for neuroimaging, different types of transparent neural implants have been proposed to resolve these issues. However, reproducing proposed solutions is often challenging and it remains unclear which approach offers the best properties for long-term chronic multimodal recordings. We therefore created a streamlined fabrication process to produce, and directly compare, two types of transparent surface micro-electrocorticography (mu ECoG) implants: nano-mesh gold structures (m-mu ECoGs) versus a combination of solid gold interconnects and PEDOT:PSS-based electrodes (pp-mu ECoGs). Both implants allowed simultaneous multimodal recordings but pp-mu ECoGs offered the best overall electrical, electrochemical, and optical properties with negligible photo-induced artefacts to light wavelengths of interest. Showing functional chronic stability for up to four months, pp-mu ECoGs also allowed the simultaneous functional mapping of electrical and calcium neural signals upon visual and tactile stimuli during widefield imaging. Moreover, recordings during two-photon imaging showed no visible signal attenuation and enabled the correlation of network dynamics across brain regions to individual neurons located directly below the transparent electrical contacts.

Automated summary

The combination of electrophysiology and neuroimaging methods allows simultaneous measurement of electrical activity signals with calcium dynamics in vivo. Transparent neural implants have been proposed to overcome limitations of traditional techniques, but their effectiveness remains unclear. This study compared two types of transparent surface micro-electrocorticography (mu ECoG) implants and found that the combination of solid gold interconnects and PEDOT:PSS-based electrodes offered the best overall properties for long-term chronic multimodal recordings. These implants showed functional stability for four months and allowed simultaneous mapping of electrical and calcium neural signals during imaging.