In a first, scientists track 1 million neurons almost simultaneously in a mouse brain

The researchers managed to keep tabs on 1 million different neurons in the brains of mice at the same time, which took scientists one step closer to being able to track the highly complex activity of the human brain.

The key is an innovation called “light bead microscopy”. It improves the current two-photon microscopy, using lasers to trigger the fluorescence introduced into living cells. When cells are lit, scientists can see how they move and interact.

Using light-bead microscopy, scientists can get the speed, scale, and resolution needed to map a mouse’s brain in detail as its neural activity changes. Near-simultaneous tracking can last as long as the light balls can stay illuminated.

“Understanding the nature of the brain’s densely interconnected network requires the development of new imaging techniques capable of capturing the activity of neurons in very distant brain regions at high speed and single-cell resolution,” explains neuroscientist Alipasha Vaziri, of Rockefeller University in New York.

“We need to capture many neurons in distant parts of the brain at the same time at high resolution. These parameters are almost mutually exclusive.”

In other words, current microscopy techniques have to choose between zooming in to get enough detail and missing out on everything that’s going on, or zooming out to see the whole image and lose some of the. finer details.

Light bead microscopy is able to overcome these limitations by removing the dead time between laser pulses – using a cavity of mirrors, it divides each strong pulse into 30 smaller subpulses of different strengths, which are then all capable of ” reach different depths while maintaining the same level of fluorescence.

This means that multiple depths can be visualized in the same pulse, giving scientists a deeper and faster glimpse of what’s going on. Scientists have now demonstrated the technique to track 1 million neurons at a time in a mouse brain.

“There is no good reason why we didn’t do it five years ago,” Vaziri said. “It would have been possible – the microscope and laser technology were there. Nobody thought about it.”

Using light-bead microscopy, scientists hope to be able to track interactions between sensory, motor and visual regions of the brain, not only in mice but also in other animals.

Interpreting and understanding the neuronal activity that is recorded will require another step forward, but the new study advances the idea of ​​what is possible with this type of microscopic analysis.

The better we can see inside the brain, the better we can understand how it works, whether it’s the interaction between individual nerve cells or finding out which parts of the brain correspond to which feelings and emotions.

“Light-bead microscopy will allow us to study biological questions in a way that was not possible before,” Vaziri said.

The research was published in Natural methods.