Until now, limited penetration depth of optical microscopy has held back neuroscientists in meaningfully studying activities in the living brain.
A new optoacoustic imaging method developed at Helmholtz Zentrum München and the Technical University of Munich in Germany now for the first time enables scientists to observe millions of neurons interact in the brain — in real time and in 3D.
“Optoacoustic imaging is unique in its simultaneous excitation of the entire brain with a single interrogating laser pulse, hence, it can image faster than other methods in 3D,” explains Dr Xosé Luis Deán-Ben, postdoctoral fellow at Helmholtz and first author of the study “Functional optoacoustic neuro-tomography (FONT) for scalable whole-brain monitoring of calcium indicators,” published in Nature’s journal Light: Science & Applications.
Enabling analysis of whole brain in adult zebrafish
The team’s greatest accomplishment, according to Deán-Ben, was the analysis of whole brains of adult animals. “We could monitor the entire brain of an adult zebrafish, with a size of approximately 2 x 3 x 4 mm — or about 24 mm3,” reports the expert in multiscale functional and molecular imaging. “Current methods detecting neural activity would only analyze around one cubic millimeter.” He points out that tissue on the level of an adult zebrafish’s brain could otherwise not have been examined with current microscopy methods.
This new FONT technique, however, appears to help scientists overcome longstanding penetration barriers of optical imaging. “Optoacoustics breaks through the optical diffusion depth barrier by capitalizing on the low scattering of ultrasound, as compared with light, in biological tissues,” Deán-Ben confirms. “It is now possible to see the brain in action at depths of several millimeters to centimeters.”
Such groundbreaking imaging capability, of course, holds tremendous promises for neuroscientists. “The simultaneous observation of a large population of nerve cells is crucial for researchers searching for answers on the functioning of the brain — both in the normal state as well as in disease,” Deán-Ben says. The new method based on optoacoustics allows scientists to visualize a greater number of neurons simultaneously, in real time and in three dimensions.
FONT’s impact on future neuroscientific breakthroughs
The researcher agrees that the imaging method can greatly impact neuroscience by enabling dynamic observations at the full-brain level. “The brain sizes covered depend on light penetration, which is maximized for near-infrared wavelengths,” he says. “The development of efficient near-infrared calcium or voltage indicators may enable deeper observations that may lead to unprecedented discoveries in the mammalian brain.”
No doubt, a tremendous amount of research work lies ahead for the teams in Munich. “We aim to enhance the spatio-temporal resolution of the method in order to ideally monitor fast action potentials in individual cells,” Deán-Ben projects.
Written by Sandra Henderson, Research Editor, Novus Light Technologies Today