Monitoring of Stimulus Evoked Murine Somatosensory Cortex Hemodynamic Activity With Volumetric Multi-Spectral Optoacoustic Tomography.

Benedict Mc Larney,Oleksiy Degtyaruk,Xosé Luís Deán-Ben,Magdalena Anastasia Hutter,Daniel Razansky

doi:10.3389/fnins.2020.00536

Abstract

Sensory stimulation is an attractive paradigm for studying brain activity using various optical-, ultrasound- and MRI-based functional neuroimaging methods. Optoacoustics has been recently suggested as a powerful new tool for scalable mapping of multiple hemodynamic parameters with rich contrast and previously unachievable spatio-temporal resolution. Yet, its utility for studying the processing of peripheral inputs at the whole brain level has so far not been quantified. We employed volumetric multi-spectral optoacoustic tomography (vMSOT) to non-invasively monitor the HbO, HbR, and HbT dynamics across the mouse somatosensory cortex evoked by electrical paw stimuli. We show that elevated contralateral activation is preserved in the HbO map (invisible to MRI) under isoflurane anesthesia. Brain activation is shown to be predominantly confined to the somatosensory cortex, with strongest activation in the hindpaw region of the contralateral sensorimotor cortex. Furthermore, vMSOT detected the presence of an initial dip in the contralateral hindpaw region in the delta HbO channel. Sensorimotor cortical activity was identified over all other regions in HbT and HbO but not in HbR. Pearson’s correlation mapping enabled localizing the response to the sensorimotor cortex further highlighting the ability of vMSOT to bridge over imaging performance deficiencies of other functional neuroimaging modalities.

Highlights

Imaging the brain with high resolution, both at functional and anatomical levels, and in real time is essential for unraveling the mysteries of how we think and act
VMSOT Monitoring of Cortical Hemodynamics being repeated in succession to efficiently cover the relatively slow hemodynamic changes for a trial length of 200 s with multiple repeats
As can be seen in the traces the hemodynamic changes clearly evince that stimulating the paw results in hemodynamic activity across the entire isocortex, with the CL side of the brain undergoing the strongest reaction, especially the contralateral hindpaw (CL-HP) region

Summary

Introduction

Imaging the brain with high resolution, both at functional and anatomical levels, and in real time is essential for unraveling the mysteries of how we think and act. The brain is known to consist of billions of cells, predominantly neurons, glia, and endothelial cells, where neuronal communication is achieved vMSOT Monitoring of Cortical Hemodynamics through electrical signals transmitted across a hugely dense network. Monitoring these orchestral interactions at a global level in mammalian brains remains a major challenge in neuroscience and current research efforts are transitioning to enable imaging the functioning brain in its entirety as opposed to focusing on single or small numbers of cells (Fornito et al, 2015; Mott et al, 2018). The method’s spatial and temporal resolution is limited while quantification of hemodynamic responses further relies upon theoretical models to extract reduced hemoglobin (HbR) levels from the measured blood oxygenated level dependent (BOLD) signals, the relationship of which to neuronal activity is still not fully understood (Arthurs and Boniface, 2002; Iannetti and Wise, 2007; Logothetis, 2008)

Methods

Results

Conclusion