Researchers Have Preserved An Entire Rabbit Brain

The five-year race to preserve every neuron in the brain has come to a successful close

Rabbit brain 4
Robert McIntyre taking a rabbit brain out of a -135 degrees Celsius freezer unit after overnight storage. The brain is completely solid.Kenneth Hayworth/The Brain Preservation Foundation

Five years ago, a non-profit organization called the Brain Preservation Foundation (BPF) challenged the world’s neuroscience community to a tough task: to preserve a mouse brain (or a mammalian brain of equal size) for extreme long-term storage. All the neurons and synapses within it would have to remain intact and visible while viewed under a special electron microscope. If achieved, the accomplishment would allow scientists not only to have a better way of studying and possibly treating brain diseases, but it would also pave the way to the idea that we might someday be able to preserve the memory stored in the brain's trillions of microscopic connections.

Today, BPR has announced that a project done by 21st Century Medicine and led by Robert McIntyre, a recent graduate of MIT, has won the prize and brought the five-year race to a successful end. The team was awarded $26,735 for their work.

McIntyre and his team figured out how to preserve the brain's circuitry by using strong chemicals to first fixate or suspend the neurons and synapses, and then chilling them to extremely cold temperatures. His technique, called "Aldehyde-Stabilized Cryopreservation", was published this past December in the journal Cryobiology. It was then reviewed by a group of judges that included the foundation's president, Kenneth Hayworth, a neuroscientist at the Howard Hughes Medical Institute. "Every neuron and synapse looks beautifully preserved across the entire brain," Hayworth said in a press release.

The key step in McIntyre’s technique, which sets it apart from others proposed, is the use of a toxic chemical called glutaraldehyde (currently used as an extremely strong disinfectant). As glutaraldehyde rapidly spreads throughout the rabbit’s brain it stops decay and fixes the protein within the brain’s vascular system in place. This stabilizes the tissue and creates an intact brain that, when stored at -135 degrees celsius, could be successfully preserved for centuries.

rabbit brain

Robert McIntyre placing the rabbit brain in a -135 degrees Celsius freezer unit.

Kenneth Hayworth/The Brain Preservation Foundation

McIntyre says the technique was originally proposed in a book called Engines of Creation by engineer Eric Drexler, in 1986, but Drexler didn't pursue it any further. In 2010, Greg Fahy, the chief scientific officer of 21st Century Medicine, used the technique in experiments to preserve kidneys. And then in 2014, McIntyre began to perfect the technique in small mammal brains.

The classic idea of cryonics—putting a terminally ill person into long-term stasis so that one day, when better technology exists, he or she could be revived and potentially cured—is still largely unachievable. So neuroscientists have funneled their resources into a more pragmatic goal: preserving the brain's "connectdome," or all of its neurons and synaptic connections, only.

When our brains form new memories, says McIntyre, that memory formation is equal to an increase in the size of our synapses. So preserving a brain’s connectome theoretically preserves memories as well. The hope is that we might one day find a way to upload the information and memories stored within an intact brain. “We know that it can be stored for centuries and not decay,” says McIntyre. “What if we image the tech we have now, but a million times faster. It’s not absurd.”

In the meantime, scientists might use the technique to study how the brain works in a much more detailed way, allowing them to better understand and treat diseases. For example, it might reveal details, like the formation of neural plaques, that are difficult to observe in Alzheimer's. The technique might also enable researchers to develop better artificial intelligence: A complete picture of the brain's circuitry could serve as a model for how artificial intelligence could work in the future.

For now, the next step is to perfect this technique in larger mammals, which is the second half of the BPF's challenge. And that could serve as a model for how the technique might be used in humans. McIntyre's group has already preserved a pig's brain, but the prize's judges have yet to examine it. In January, McIntyre formed the company Nectome to continue with this research.

How long this research will take and whether a human brain—and all of the memories and information it contains—will ever be preserved successfully remains to be seen. But McIntyre is optimistic about his technique and the field of cryonics in general. “The timeline of this is not written in stone,” he says. But “in an ideal world, we would envision a future, where if you are facing end of life, you could have your brain preserved at this level of detail.”