New microscopy technique peers deep into the brain

A novel microscopy technique, developed by Rockefeller scientists from the lab of Alipasha Vaziri, IMP adjunct investigator, integrates new and existing approaches to help build a more cohesive picture of the brain. Described in Cell, the technology captures cellular activity across large volumes of neural tissue, with impressive speed and at new depths.

For decades, brain imaging has been plagued by trade-offs. Some techniques produce high-quality images, but fail to record brain 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 trade-offs have not been explored or pushed in a systematic and integrated manner", says Alipasha Vaziri, head of the Laboratory of Neurotechnology and Biophysics at the Rockefeller University and IMP adjunct investigator.

Hoping to end the era of trade-offs, Vaziri recently endeavoured to improve upon a technique known as two-photon (2p) microscopy. 2p involves the application of a laser that causes bits of brain tissue to fluoresce, or light up; and for many researchers, it 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 rates. Another weakness is that 2p microscopy 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.

Taking up this challenge, Vaziri decided to make use of a newer technology: three-photon (3p) microscopy. Whereas 2P does not 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.

Deep dive

The goal of this endeavour, 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 speeds. And whereas previous techniques scanned only a single plane of tissue, this technology can obtain information from as many as 12,000 neurons at once. Another advantage of HyMS is its ability to simultaneously measure activity from brain area 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.

"To understand the dynamics of a neural network", Vaziri says, "you need to get accurate measurements of big portions of the brain at a single neuron level. That’s what we’ve done here."

Original Publication

Weisenburger, S. et al. (2019). Volumetric Ca2+ Imaging in the Mouse Brain using Hybrid Multiplexed Sculpted Light (HyMS) Microscopy. Cell, 8 April 2019 (Epub ahead of print)
DOI: 10.1016/j.cell.2019.03.011

Further reading

More about Alipasha Vaziri's lab at the Rockefeller University (origin of this study)
More about Alipasha Vaziri's lab at the IMP