The science media have been ablaze recently with a major achievement: Princeton neuroscientists have mapped the staggering complexity of a cubic millimetre of the visual area of a mouse’s brain — about a poppy seed’s worth. That was a remarkable achievement on account of the complexity of even a mouse’s brain.

PBS tells us that the mouse gave the scientists’ data by watching, among other things, The Matrix: (1999):

Thanks to a mouse watching clips from “The Matrix,” scientists have created the largest functional map of a brain to date – a diagram of the wiring connecting 84,000 neurons as they fire off messages.

Using a piece of that mouse’s brain about the size of a poppy seed, the researchers identified those neurons and traced how they communicated via branch-like fibers through a surprising 500 million junctions called synapses.

The massive dataset, published Wednesday by the journal Nature, marks a step toward unraveling the mystery of how our brains work. The data, assembled in a 3D reconstruction colored to delineate different brain circuitry, is open to scientists worldwide for additional research – and for the simply curious to take a peek.

“How a mouse watching ‘The Matrix’ helped scientists create the largest map of a brain to date,” April 9, 2025 The papers from the project are here.

At the New York Times, science writer Carl Zimmer provides a bit of perspective:

The human brain is so complex that scientific brains have a hard time making sense of it. A piece of neural tissue the size of a grain of sand might be packed with hundreds of thousands of cells linked together by miles of wiring. In 1979, Francis Crick, the Nobel-prize-winning scientist, concluded that the anatomy and activity in just a cubic millimeter of brain matter would forever exceed our understanding.

“It is no use asking for the impossible,” Dr. Crick wrote.

Forty-six years later, a team of more than 100 scientists has achieved that impossible, by recording the cellular activity and mapping the structure in a cubic millimeter of a mouse’s brain — less than one percent of its full volume. In accomplishing this feat, they amassed 1.6 petabytes of data — the equivalent of 22 years of nonstop high-definition video.

“An Advance in Brain Research That Was Once Considered Impossible”, April 9, 2025

But, for the sake of science, as Margherita Bassi notes at Smithsonian Magazine, the mouse’s career as a film critic was abruptly ended…

The researchers then extracted a cubic millimeter of brain tissue and sliced it into roughly 28,000 layers—each about 400 times thinner than a human hair. They photographed each layer, used artificial intelligence to process the images into a digital 3D diagram and combined it with the previously recorded brain activity patterns associated with vision.

Because they had studied how the mouse’s neurons lit up as it watched videos, the team could compare the neurons’ mapped structure with their functions and piece together how the connections between them work.

While scientists had previously studied brain cells’ structure and function separately, “understanding how neuronal function emerges at the circuit level has been challenging, since we need to study both function and wiring in the same neurons,” Andreas Tolias, a neuroscientist at Baylor College of Medicine and one of the lead researchers, tells Reuters’ Will Dunham.

“In a World First, Researchers Mapped Part of a Mouse’s Brain in Incredible Detail. It’s a Leap Forward for Neuroscience,” April 10, 2025

Materialism’s last stop: The Matrix

The underlying message of Zimmer’s article is that the human brain is really the same sort of thing, just more complex, and we will reduce it to a map. And, although no one quite says it, the human mind is to be understood as merely the output of a complex brain: The news release from Princeton made that clear:

“It’s just a beginning,” [team co-lead] Seung said. “But it’s opening the door to a new era of realistic brain simulations. And so the next question becomes — and people will ask — can that ever be done with a human brain? And then the next question is, well, even if you could simulate a human brain, and it was very faithful, would it be conscious?”

When asked what he thought about it, he laughed. “I don’t have any more authority to make a statement on that than you do. But when people say, ‘I don’t believe a simulation of a brain would be conscious,’ then I say, ‘Well, how do you know you’re not a simulation?’”

Scott Lyon, “Scientists map the half-billion connections that allow mice to see,” April 9, 2025

The problem with Seung’s reasoning is, of course, this: If we don’t know that we are not simulations, we also don’t know that anything we think we know is real. Life in The Matrix is a high price to pay in order to maintain a materialist view of the mind.

And if it takes a hundred scientists to map a cubic millimetre of a mouse’s brain, even the material world — never mind the immaterial world of the mind — is not likely to have a simple explanation.

Here’s a key scene from The Matrix (1999):