The biggest and most detailed three-dimensional map of a mammal's brain ever created provides unparalleled understanding of neuron connections and functions. This new map, depicting one cubic millimeter of a mouse's visual cortex, enables researchers to examine brain operations with remarkable precision. It could potentially uncover vital information about how neural actions influence behavior, how intricate characteristics such as consciousness develop, and ultimately, what defines our humanity.
"Our behaviors essentially stem from neural activities within the brain, and brain tissues exhibit highly comparable characteristics across all mammalian species," explains the team member. Forrest Collman At the Allen Institute for Brain Science in Seattle, they say, "This is why we think understanding the mouse cortex can be applied to humans."
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The accomplishment – something that biologists In 1979, Francis Crick stated that it was "impossible." —spanned seven years and included contributions from 150 scientists at three different institutions. The project started with a group capturing neural activity from an incredibly small section of a mouse's visual cortex, roughly the size of a grain of sand, while it viewed various movies and YouTube videos.
Following suit, another group divided the identical brain area into slices as thin as 1/400th the diameter of a human hair and photographed every individual layer. Given the fragility of the structure, they had to keep the cutting continuous; thus, the researchers worked around the clock. "It took us 12 consecutive days and nights to cut this cubic millimeter of tissue into nearly 30,000 sections," explains one team member. Nuno da Costa , as well as at the Allen Institute.
Next, a third group employed artificial intelligence to track all the cells and transform each section into a 3D map. "This task felt akin to tackling the most difficult coloring book globally," states Collman. "Imagine you're dealing with 100 million pictures across three dimensions, requiring distinct colors for every individual cell. The AI must determine precisely when one cell ends and another begins."
The collected information was ultimately merged with the functional activity documented at the beginning of the initiative, enabling a connection between the visual stimuli observed by the mouse and the related neural activities within its brain. This produced a chart highlighting the astounding intricacy of this organ. Although small in stature, it encompasses over 200,000 neurons interconnected through approximately four kilometers of branching structures, along with an impressive 523 million synaptic connections linking these cells.
The data is already challenging assumptions about how neurons communicate, revealing that they not only target nearby cells, but actively hunt out other cells dedicated to processing the same visual stimuli.
The research team anticipates that their mapping effort will help close some of the gaps in understanding between neural activity and behaviors, ultimately aiding in decoding intricate characteristics such as intelligence. "This is pioneering work that will prove extremely valuable to the scientific community," remarks. Nathalie Rochefort at the University of Edinburgh in the UK.
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According to da Costa, beyond its direct uses, we may also have the opportunity to examine various theories of consciousness. "Should someone propose a theory of consciousness, they could pose queries about this dataset. This process might either lend credibility to their theory or disprove it," she suggests.
The research expands upon an additional study released in the previous year that charted each neuron in the mature fruit fly brain —a milestone that has already transformed the industry, according to Rochefort. For example, it has assisted researchers. gain better insight into the circadian rhythms influencing various aspects from sleep to metabolism.
She states that this new map will be incredibly valuable, enabling scientists to compare it with other maps from various species. This comparison aims to identify which cells, neural wiring patterns, and functions are unique to individual species or common among multiple ones, "eventually illuminating what sets humans apart."
The project is released as a sequence of parts. eight articles in Nature publications .