Scientists revive activity in frozen mouse brains for the first time

Scientists revive activity in frozen mouse brains for the first time

By Tosin Thompson & Nature magazine

A familiar trope in science fiction is the cryopreserved time traveller, their bodies deep-frozen in suspended animation, then thawed and reawakened over the course of a decade or century with all their mental and physical abilities intact.

Researchers attempting to cryogenically freeze and thaw brain tissue from humans and other animals — mostly young vertebrates — have already shown that neuronal tissue can survive freezing at the cellular level and, after thawing, function to some degree. But it has not been possible to fully restore the processes necessary for proper brain function – neuronal firing, cell metabolism and brain plasticity.

A team in Germany has now demonstrated a method for cryopreservation and thawing of mouse brains that leaves some of this functionality intact. The study, published on March 3 in Proceedings of the National Academy of Sciencesdescribes the authors’ use of a method called vitrification, which preserves tissue in a glass-like state, along with a thawing process that preserves living tissue.

On supporting science journalism

If you like this article, please consider supporting our award-winning journalism by subscribes. By purchasing a subscription, you help secure the future of impactful stories about the discoveries and ideas that shape our world today.

“If brain function is an emergent property of its physical structure, how can we restore it from complete shutdown?” asks Alexander German, neurologist at the University of Erlangen–Nuremberg in Germany and lead author of the study. The findings, he says, suggest the potential to one day protect the brain during disease or in the aftermath of severe injury, set up organ banks and even achieve whole-body cryopreservation of mammals.

Mrityunjay Kothari, who studies mechanical engineering at the University of New Hampshire in Durham, agrees that the study advances the latest in brain tissue cryopreservation. “This kind of progress is what gradually turns science fiction into a scientific possibility,” he says. However, he adds that applications such as long-term tapping of large organs or mammals remain well beyond the study’s capabilities.

Preserved for the future

The main reason why the brain struggles to fully recover from freezing is due to damage caused by the formation of ice crystals. These displace or puncture the tissue’s delicate nanostructure, and disrupt central cellular processes. “Beyond ice, we have to take into account several considerations, including osmotic stress and toxicity due to cryoprotectants,” says German.

German and his colleagues turned to an ice-free method of cryopreservation called vitrification in an attempt to preserve brain function. Vitrification cools liquids quickly enough to trap molecules in a disorganized, glass-like state before they have a chance to form ice crystals. “We wanted to see if function could restart after the complete cessation of molecular mobility in the vitreous,” says German.

They first tested their method on 350-micron-thick slices of mouse brains that included the hippocampus—a core brain node for memory and spatial navigation. Brain slices were pretreated in a solution containing cryopreservation chemicals before being rapidly cooled with liquid nitrogen at -196 ºC. They were then stored in a freezer at -150 ºC in a glass-like state for between ten minutes and seven days.

After thawing the brain slices in warm solutions, the team analyzed the tissue to see if it had retained any functional activity. Microscopy showed that neuronal and synaptic membranes were intact, and tests for mitochondrial activity revealed no metabolic damage. Electrical recordings of neurons showed that, despite moderate abnormalities compared to control cells, the neurons’ response to electrical stimuli was close to normal.

Hippocampal neuronal pathways still showed the synaptic strengthening or “long-term potentiation” that underlies learning and memory. But because such disks break down naturally, the observations were limited to a few hours.

The team scaled up the method to the whole mouse brain, keeping it in a glassy state at -140 ºC for up to eight days. However, the protocol needed repeated adjustments to minimize brain shrinkage and toxicity from cryoprotectants.

Once the brain was thawed, brain slices were prepared and recordings from the hippocampus confirmed that neuronal pathways—including hippocampal pathways involved in memory—had survived and could still undergo long-term potentiation. But because the recordings were made using slices of brain tissue, the researchers were unable to measure whether the animals’ memories had survived cryopreservation.

Still science fiction

German and his team extend the method from mice to human brain tissue. “We already have preliminary data showing viability in human cortical tissue,” he says. The team is also investigating how the vitrification method can be used for cryopreservation of whole organs, especially for the heart.

However, Kothari points out that the success rate was low on the whole-brain protocol, and that the results may not translate directly to larger human organs, which present other challenges. “Some of these challenges are related to heat transfer limitations and higher thermomechanical stresses that can cause cracking,” says Kothari.

German adds that “better vitrification solutions and cooling and heating technologies will be needed before these principles can be applied to large human organs.”

This article is reproduced with permission and var first published March 11, 2026.

It’s time to stand up for science

If you liked this article, I would like to ask for your support. Scientific American has served as an advocate for science and industry for 180 years, and right now may be the most critical moment in its two-century history.

I have been one Scientific American subscriber since I was 12 years old, and it helped shape the way I see the world. SciAm always educates and delights me, and inspires a sense of awe for our vast, beautiful universe. I hope it does for you too.

If you subscribe to Scientific Americanyou help ensure our coverage is centered on meaningful research and discovery; that we have the resources to report on the decisions that threaten laboratories across the United States; and that we support both budding and working scientists at a time when the value of science itself is too often not recognised.

In return, you receive important news, captivating podcasts, brilliant infographics, can’t-miss newsletters, must-see videos, challenging games, and the world of science’s best writing and reporting. You can even give someone a subscription.

There has never been a more important time for us to stand up and show why science is important. I hope you will support us in that mission.