Optimizing intact skull intrinsic signal imaging for subsequent targeted electrophysiology across mouse visual cortex

Armel Nsiangani,Donghoon Shin,Shea Wells,Tidhar Lev-Ari,Bilal Haider,Joseph Del Rosario,Alan C Yeh,Brice Williams

doi:10.1038/s41598-022-05932-2

Armel Nsiangani, Donghoon Shin + Show 6 more

Open Access

https://doi.org/10.1038/s41598-022-05932-2

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Abstract

Understanding brain function requires repeatable measurements of neural activity across multiple scales and multiple brain areas. In mice, large scale cortical neural activity evokes hemodynamic changes readily observable with intrinsic signal imaging (ISI). Pairing ISI with visual stimulation allows identification of primary visual cortex (V1) and higher visual areas (HVAs), typically through cranial windows that thin or remove the skull. These procedures can diminish long-term mechanical and physiological stability required for delicate electrophysiological measurements made weeks to months after imaging (e.g., in subjects undergoing behavioral training). Here, we optimized and directly validated an intact skull ISI system in mice. We first assessed how imaging quality and duration affect reliability of retinotopic maps in V1 and HVAs. We then verified ISI map retinotopy in V1 and HVAs with targeted, multi-site electrophysiology several weeks after imaging. Reliable ISI maps of V1 and multiple HVAs emerged with ~ 60 trials of imaging (65 ± 6 min), and these showed strong correlation to local field potential (LFP) retinotopy in superficial cortical layers (r2 = 0.74–0.82). This system is thus well-suited for targeted, multi-area electrophysiology weeks to months after imaging. We provide detailed instructions and code for other researchers to implement this system.

Highlights

Understanding brain function requires repeatable measurements of neural activity across multiple scales and multiple brain areas
Our intrinsic signal imaging (ISI) protocol is inspired by prior w ork[2,5], but provides two major improvements tailored for ISI integration with subsequent multi-site electrophysiology
We found that the 5 mm coverslip bonded inside a headplate with an 11 mm circular opening (Fig. S2) provided a highly repeatable and mechanically stable platform for ISI, subsequent cranial window removal, and multiple sessions of mechanically stable high-quality electrophysiology recordings

Summary

Introduction

Understanding brain function requires repeatable measurements of neural activity across multiple scales and multiple brain areas. Pairing ISI with visual stimulation allows identification of primary visual cortex (V1) and higher visual areas (HVAs), typically through cranial windows that thin or remove the skull These procedures can diminish long-term mechanical and physiological stability required for delicate electrophysiological measurements made weeks to months after imaging (e.g., in subjects undergoing behavioral training). Reliable ISI maps of V1 and multiple HVAs emerged with ~ 60 trials of imaging (65 ± 6 min), and these showed strong correlation to local field potential (LFP) retinotopy in superficial cortical layers (r2 = 0.74–0.82) This system is well-suited for targeted, multi-area electrophysiology weeks to months after imaging. No study has optimized ISI for intact skull conditions in adult mice, quantified the minimum sample size (imaging duration) necessary for reliable and repeatable maps of V1 and HVAs, verified these retinotopic maps directly with electrophysiological measurements. Protocol, and codebase are all made publicly available, providing a useful tool for investigators wishing to pair minimally invasive transcranial ISI with subsequent targeted electrophysiology in the mouse visual system

Methods

Results

Conclusion