Understanding brain functionality remains an arduous task despite decades of research employing a wide array of neural recording and imaging techniques. Genetically encoded calcium indicators (GECIs) are powerful and versatile tools for tagging fast neural activity in a large number of neurons with excellent spatial localization. Here we demonstrate that functional optoacoustic neuro-tomography (FONT) enables non-invasive imaging of sensory-evoked activity in GCaMP6-expressing mouse brain in vivo, thus holding promise for large-scale neural recording at penetration depths and spatio-temporal resolution scales not covered with the existing neuroimaging techniques. The FONT imaging system has volumetric temporal resolution of 10msec and spatial resolution of 150µm across an effective field of view of 2cm3 covering an entire mouse brain. However, the effective depth in the current study was restricted to the cortical areas due to the limited penetration of light at the visible wavelengths used for the GCaMP6 excitation. The stimulation protocol involving somatosensory electrical hindpaw stimulation was specifically designed to minimize the influence of hemodynamic changes indirectly associated with neuronal activity, which are much slower than the GCaMP-related calcium transients. Rapid optoacoustic signal transients were observed in the activated brain regions but not inside major blood vessels, thus allowing for a clear differentiation of the calcium-related activity from the underlying hemodynamic responses. Our study is the first to examine fast volumetric optoacoustic signatures of GECIs non-invasively in living mice, further showing that the corresponding changes of their fluorescence are directly related to the optoacoustic responses.
Sven Gottschalk, Xose Luis Deán-Ben, Shy Shoham, and Daniel Razansky, "Real-time volumetric mapping of calcium activity in living mice by functional optoacoustic neuro-tomography (Conference Presentation)," Proc. SPIE 10494, Photons Plus Ultrasound: Imaging and Sensing 2018, 104941I (Presented at SPIE BiOS: January 30, 2018; Published: 15 March 2018); https://doi.org/10.1117/12.2289685.5752212565001.
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