Scientists have for the first time in history managed to "resurrect" a frozen brain

German scientists have taken an important step toward creating technologies for cryopreservation of complex organs. They managed to restore functional activity of brain tissue after deep freezing. The work was published in the journal Proceedings of the National Academy of Sciences (PNAS).

For a long time, the formation of ice crystals was considered the main obstacle to freezing the brain. When water inside cells turns into ice, the crystals destroy cell membranes and damage connections between neurons. As a result, the tissue loses its ability to function normally after thawing.

Researchers from the University of Erlangen-Nuremberg overcame this problem using a method called vitrification — ultra-rapid cooling of tissue in which no ice forms. Instead of crystallizing, the liquids inside cells transition into a glass-like state, virtually completely halting molecular movement and preserving the tissue's structure.

In the experiment, the scientists used thin slices of mouse hippocampus — a brain region that plays a key role in learning and memory. The samples were cooled with liquid nitrogen to a temperature of approximately −196 °C and stored in that state for periods ranging from ten minutes to one week.

After that, the tissue was carefully thawed. Analysis showed that the cell membranes of neurons and synapses were preserved. In addition, mitochondria — structures that supply cells with energy — functioned normally.

The most important result was that the neurons once again exhibited electrical activity. The cells responded to electrical stimulation almost the same way as in unfrozen samples.

The scientists also detected signs of long-term potentiation — a process of strengthening synaptic connections that is considered the cellular basis of learning and memory. This means that after freezing, not only individual cells were preserved, but also some elements of neural networks.

To achieve this result, the researchers used a special set of cryoprotective substances, which were introduced into the tissue gradually to avoid damage. After freezing, the samples were warmed very rapidly — at a rate of approximately 80 °C per second, which prevented ice formation during thawing.

The scientists also attempted to apply the technology to an entire mouse brain. The main difficulty turned out to be the blood-brain barrier — the brain's natural protective system that prevents the penetration of large molecules. To solve the problem, the researchers alternately perfused protective substances and a special carrier solution through the blood vessels.

So far, the experiments have only been conducted on thin tissue slices, and observations lasted just a few hours after thawing. However, the results show that key brain structures are capable of surviving freezing significantly better than previously believed.

According to the specialists, such technologies are still far from being applicable for human "cryosleep" or long-term storage of entire organisms. Nevertheless, the research could open new possibilities in medicine — for example, for preserving organs before transplantation or protecting the brain after severe injuries.

"Such progress is gradually turning science fiction into scientific possibility," noted cryobiology specialist Mrityunjai Kothari.