How One Rat Managed To See, Hear, Smell, And Feel With Most Of Its Brain Missing

clockJan 23 2020, 23:39 UTC

Craig Ferris, professor of psychology, points at a scan of a normal rat’s brain. In contrast, the important parts of R222’s brain collapsed and relocated, concealing major glands and regions from even the most trained eye. Ruby Wallau/Northeastern Univers

On the outside, R222 is a 2-year-old lab rat that looks like any other. He acted like any other rat, smelling his way around his cage, seeing and hearing and feeling as any other rat might. But for R222’s entire life, this experimental rodent has been hiding a neurological secret: a highly deteriorated, compressed brain that would otherwise render the animal completely inept.

That’s because R222 suffered from a severe case of hydrocephalus, a buildup of fluid in the ventricles, or fluid-containing cavities of the brain, that puts pressure on the organ. In the rat’s case, the condition was so severe that its brain had compressed and collapsed on itself. In most cases, hydrocephaly can cause debilitating cognitive and motor problems and a shortened lifespan, while others may exhibit no personality changes.


Scientists came across this natural “miracle” during a study on aging at the Center for Translational Neuroimaging at Northwestern University. At the beginning of their work, researchers were scanning the brains of very old rats when it was revealed that R222’s severely cortex was severely thinned and replaced by cerebrospinal fluid and his hippocampus was compressed and likely had been since the animal’s birth.

To determine how R222 held up against other rats in his cohort, researchers placed each rodent in a Plexiglass box to see how they responded to new stimuli placed within. They then observed rats as they navigated through a maze and how well they balanced on a beam – all tests to evaluate spatial and motor skills as well as memory. With the exception of exploring a new environment, R222 performed just as well as the other rats.

Brain and Cortical Volumes. Shown is the average total brain volume (brain and CSF filled ventricles) of five age-matched controls and R222. The MR images depict the actual size of R222’s brain as compared to that of an age-matched control with the cortices in each highlighted in red. Scientific Reports

But how could a rat with no brain act like a rat with a fully intact one? Neuroplasticity. Though it’s an extremely rare case, the researchers say that R222 is a prime example of how a brain can reorganize itself when absolutely necessary. Rather than information being processed in small parts across the entire expanse of the brain, the researchers saw that information was processed across the entirety of R222's very small, collapsed brain. R222 was operating at the “bare minimum” for most of its life – its brain was distorted and essential areas, such as the hippocampus, were not even discernable in brain scans. It was only by tracing chemical signals that researchers were able to verify their squished, distorted locations.

"The lower part of the brain stem had everything collapsed in it," said researcher Craig Ferris in a statement. "This animal just defaulted to what evolution gave it in the beginning, along with all the other animals, to help it survive."


Of course, the rat lived in a controlled environment for two years and did not need to act on any real life-threatening scenarios. But researchers concluded that R222’s ability to adapt neurologically lends information to how brains may function and change over the course of our lives.

"One of the things I always get a kick out of is the hubris that we have about how highly organized our brain is – and how complex it is," Ferris said. "We've really focused so much attention on the cortex, and here you have these cases where you can almost eliminate the cortex – large portions of it – and it's not making a heck of a lot of difference."

The jury is still out as to why R222 suffered such a severe case of hydrocephaly in the first place, though the researchers speculate that it could have been a genetic mutation at birth. The findings are published in Scientific Reports

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