Mice Watching “Touch of Evil” Teach Scientists About the Mind’s Eye

By tracking mice neurons, scientists hope to understand consciousness

Brain Observatory
Researchers show a mouse an image of cat while recording neuron activity in its visual cortex Allen Institute

Close your eyes. What do you see? The images that form are all part of a conscious mental landscape. But how the brain processes the world around you remains a mystery to science.

In the past, teasing out the intricacies of how the human brain makes sense of visual input was close to impossible. It was not until recently that scientists could directly observe individual neurons at work. Now the Allen Institute for Brain Science in Seattle is launching the Allen Brain Observatory to use this new technology to investigate cognition in an unusual manner: they make mice watch movies. 

The project involves 25 lab mice that are genetically engineered so their neurons light up when fired, reports Arlene Weintraub at Forbes. Each mouse also had a small window implanted in its head so researchers could observe the fluorescent neurons in their visual cortex.

The rodents ran on a treadmill while watching a clip from the opening of Orson Welles' 1958 Touch of Evil. As the images appeared on the screen in front of them, the researchers recorded their brain activity with a two-photon microscope.

Though this may seem like an unusual choice for the study, according to Jon Hamilton at NPR, this cult-classic movie's three-minute opening scene seems like it was tailor-made for the study. “It’s black and white and it has nice contrasts and it has a long shot without having many interruptions,” Christof Koch, chief scientific officer at the Allen Institute explains.

The film seemed to be a hit with the mice. R. Clay Reid, a senior investigator on the project tells Weintraub that the 18,000 monitored neurons lit up. “During the course of the movie, neurons responded to different parts of it at different times and in interesting ways,” he says. “It was quite remarkable how varied the responses of different neurons were to these stimuli.”

Allen Brain Observatory: Visualizing the brain in action

The microscope recorded when a neuron fired and its intensity. Correlating that data with the image on the screen allowed the researchers to map the function of each neuron. For instance, some neurons only fired when vertical lines appeared on the screen. Others lit up when the camera panned. The researchers also conducted several other experiments, such as showing the mice images of insects or animals and images of black and white bars, recording how the neurons responded. The project took four years and involved 360 experimental sessions, producing 30 terabytes of data, reports Helen Shen at Nature.

The research has already revealed some unusual patterns, reports Brendan Cole at Wired. The same neurons that fire when the mice look at a photo of a butterfly, for example, also lit up when the camera panned during the movie. Why exactly is not known, but the researchers at Allen hope the wider scientific community will help them figure it out.

That’s why they publicly released the data set as part of the open-source Allen Brain Atlas. That project has hosted various data on mouse and human brains since 2006 and is part of Microsoft co-founder Paul Allen’s ambitious half-billion dollar project to map the human brain.

“This is basically a bonanza,” computational neuroscientist Steven Zucker at Yale University tells Shen. “It’s as if somebody opened the door into the world’s biggest neuroscience lab for theoreticians around the world and said, ‘Come on in and play with our data.’”

Those 18,000 neurons are just a very small start. “By the time we’re finished, it will be such a complete encyclopedic dataset that’s online and that scientists can share and use as a starting point,” Reid tells Weintraub. The next step is expanding the work to monitoring the mice as they carry out other tasks. No word yet on whether that will include taking them back to the movies.

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