For decades, brain imaging has been plagued by trade-offs. Some techniques produce beautiful images but fail to record neural activity in real time. Others can keep up with the brain's speed but have poor spatial resolution. And although there are tactics that successfully combine rapidity and image quality, they typically capture only a small number of cells.
"This is in part because the limits that govern these tradeoffs have not been explored or pushed in a systematic and integrated manner," says Alipasha Vaziri, head of the Laboratory of Neurotechnology and Biophysics.
Hoping to end the era of trade-offs, Vaziri recently endeavored to improve upon a technique known as two-photon (2p) microscopy. It involves the application of a laser that causes bits of brain tissue to fluoresce, or light up; and for many researchers, 2p has long been the gold standard for probing cellular activity in the brain.
Yet, this technique has limitations. Standard 2p microscopy requires point-by-point scanning of a given region, which results in slow imaging. To resolve this issue, Vaziri and his colleagues implemented a novel strategy that permits recording from multiple brain regions in parallel, while carefully controlling the size and shape of each spot recorded.
Another weakness of traditional 2p is that it measures only the surface, or cortex, of the brain, neglecting structures buried deep within the organ, such as the hippocampus, which is involved in storing memories.
"One of the biggest challenges in neuroscience is developing imaging techniques that measure the activity of deep brain regions while maintaining high resolution," says Vaziri.
Taking up this challenge, he decided to make use of a newer technology: three-photon (3p) microscopy. Whereas 2P doesn't reach beyond the surface, or cortex, of a mouse brain, 3p penetrates deeper regions. Called hybrid multiplexed sculpted light microscopy, or HyMS, Vaziri's latest innovation applies 2P and 3P concurrently, allowing researchers to generate a picture of rapid cellular activity across multiple layers of brain tissue.
In addition to its hybrid laser strategy, HyMS also integrates other recent technical and conceptual advancements in the field--a synergistic approach that, Vaziri says, guided the development of the technology. The goal, he says, was to maximize the amount of biological information that could be obtained through multi-photon excitation microscopy while minimizing the heat produced by this method. And when testing their new system, the scientists certainly obtained a lot of information.
HyMS boasts the highest frame rate of available 3p techniques, which means it can capture biological changes at record speed. And whereas previous techniques scanned only a single plane of tissue, this technology can obtain information from the entire tissue sample and allows users to record from as many as 12,000 neurons at once. Another advantage of HyMS is its ability to simultaneously measure activity from brain areas at different depths. Since different layers of the brain constantly exchange signals, says Vaziri, tracking the interplay between these regions is key to understanding how the organ functions.
MEDICA-tradefair.com; Source: Rockefeller University
