Scientists revive activity in frozen mouse brains for the first time

Scientists revive activity in frozen mouse brains for the first time

‘Cryosleep’ remains the preserve of science fiction, but researchers are getting closer to restoring brain function after deep freezing

By Tosin Thompson & Nature magazine

A ‘cryosleep pod’ in the 1979 science-fiction film Alien.

20TH CENTURY FOX via AJ Pics/Alamy

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

Researchers attempting cryogenic freezing and thawing of brain tissue from humans and other animals — mostly young vertebrates — have already shown that neuronal tissue can survive freezing on a cellular level and, after thawing, function to some extent. However, fully restoring the processes necessary for proper brain functioning — including neuronal firing, cell metabolism, and brain plasticity — has not yet been possible.

A team in Germany has now demonstrated a method for cryopreserving and thawing mouse brains that preserves some of this functionality. The study, published on March 3 in Proceedings of the National Academy of Sciences, describes the use of a technique called vitrification, which preserves tissue in a glass-like state, combined with a thawing process that maintains living tissue.

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

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

Preserved for the future

The main obstacle to full brain recovery after freezing is damage caused by ice crystal formation. Ice crystals displace or puncture the tissue’s delicate nanostructure, disrupting key cellular processes. “Beyond ice, we must account for several considerations, including osmotic stress and toxicity due to cryoprotectants,” explains German.

To address this, German and colleagues used an ice-free cryopreservation method called vitrification. Vitrification cools liquids rapidly enough to trap molecules in a disorganized, glass-like state before ice crystals can form. “We wanted to see if function could restart after the complete cessation of molecular mobility in the vitreous state,” says German.

They first tested their method on 350-micrometre-thick slices of mouse brains, including the hippocampus — a core brain region for memory and spatial navigation. Brain slices were pre-treated with a solution containing cryopreservation chemicals, then rapidly cooled using liquid nitrogen at –196 °C. They were stored at –150 °C in a glass-like state for periods ranging from ten minutes to seven days.

After thawing the brain slices in warm solutions, the team analyzed the tissue for functional activity. Microscopy showed neuronal and synaptic membranes remained intact, and mitochondrial activity tests revealed no metabolic damage. Electrical recordings of neurons demonstrated that, despite moderate deviations compared with control cells, neuronal responses to electrical stimuli were nearly normal.

Hippocampal neuronal pathways still exhibited synaptic strengthening or ‘long-term potentiation’ — the mechanism underlying learning and memory. However, since such slices naturally degrade, observations were limited to a few hours.

The team then scaled up the method to whole mouse brains, maintaining them in a vitreous state at –140 °C for up to eight days. The protocol required repeated adjustments to minimize brain shrinkage and toxicity from cryoprotectants.

Upon thawing, brain slices were prepared and recordings from the hippocampus confirmed that neuronal pathways — including those involved in memory — survived and could still undergo long-term potentiation. However, because recordings were made from slices, the researchers could not determine whether the animals’ memories survived cryopreservation.

Still science fiction

German and his team are now extending their method to human brain tissue. “We already have preliminary data showing viability in human cortical tissue,” he says. The team is also investigating how vitrification might be applied to whole-organ cryopreservation, especially for the heart.

However, Kothari points out that the success rate was low for the whole-brain protocol and cautions that results may not directly translate to larger human organs, which present additional challenges. “Some of these challenges relate to heat-transfer constraints and higher thermo-mechanical stresses that may cause cracking,” he explains.

German adds, “Better vitrification solutions and improved cooling and rewarming technologies will be necessary before these principles can be applied to large human organs.”

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