Scientists put window in fruit fly skull to watch its brain

A composite image of fruit fly brain activity superimposed on a photo of a fly(Credit: Take Katsuki/Kalvi Institute for Brain and Mind)

How do you see what's going on in a fruit fly's mind? Why you build a window to its brain, of course. While that might sound like a bad joke, it's exactly what scientists at the University of California San Diego (UCSD) have just done. Their goal was to understand exactly what happens in the tiny creature's brain as it goes about courting a mate, unencumbered by wires or other attachments usually used to monitor its neural activity. The system they created is called "Flyception" and is amazingly complex and precise.

First, the researchers surgically removed a part of the fly's exoskeleton covering its head. According to a UCSD report about the process, the area removed was about the size of few grains of salt. Next, the gap was sealed with a transparent silicon adhesive that was topped with a coverslip – a clear, flat material usually used to view slides under a microscope. This created a window that exposed the upper half of the fly's brain known as the protocerebrum.

Next came the really tricky part. Because flies aren't known for staying still, the researchers had to figure out a way to look inside that window to monitor brain activity as the fly got in a romantic state of mind. To do this, they created a special viewing platform monitored by three cameras and a series of rotating mirrors.

As the fly moves around, two different cameras track the window on its skull and control the position of the mirrors so that the fly's head stays centered in the view. Then, a laser is bounced off the mirrors to strike the fly's brain where fluorescent calcium markers light up to identify specific neurons in the brain. While we've seen fluorescent neural tracking before in fruit flies, the complexity of this system and the real-time feedback delivered at 1,000 frames per second is certainly new.

"One of the biggest goals of today's neuroscience research – as outlined by the national BRAIN Initiative – is to map brain activity at a whole brain scale in naturally behaving animals, so that we can understand how higher-order cognitive functions, and disorders, emerge through the concerted activity of multiple brain regions," says UCSD's Takeo Katsuki, assistant project scientist with the university's Kavli Institute for Brain and Mind. "The technology we developed provides a first step toward this goal by enabling monitoring brain activity in naturally behaving fruit flies."

Katsuki is a co-author on a paper about the Flyception system published on May 16 in the journal Nature Methods.

According to UCSD, studying the brains of fruit flies is advantageous because they are relatively small, having only about 100,000 neurons, but they are complex enough to allow researchers to track different behaviors as the flies interact with their environments and others of their kind. This brief video shows the new system in action as a male fly engages in one such interaction – singing a mating song as he pursues a female.

Source: UC San Diego

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