雅思阅读 093: Thawing Frozen Mice

Adapted from 'Scientists revive activity in frozen mouse brains for the first time', Scientific American, March 2026.

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In science fiction, travellers freeze their bodies in suspended animation, then thaw centuries later with all their mental faculties intact. Researchers have already shown that individual brain cells can survive freezing and partial thawing. But fully restoring the processes necessary for proper brain function has remained beyond reach.

A team in Germany has now demonstrated a method called vitrification that preserves mouse brains in a glass-like, ice-free state. After thawing, some memory circuits still function. The study was published in Proceedings of the National Academy of Sciences.

The main obstacle to freezing is ice crystals. As water freezes, it forms sharp crystals that puncture delicate cell membranes. Vitrification solves this by cooling tissue so rapidly with liquid nitrogen at minus 196 degrees Celsius that water molecules freeze into a disordered, glass-like solid before crystals can form.

The researchers first tested the method on thin slices of mouse brain containing the hippocampus, a region critical for memory. The slices were treated with chemical antifreeze, plunged into liquid nitrogen and stored at minus 150 degrees Celsius for up to seven days. After thawing, neurons responded to electrical stimuli near normally, and the brain slices still showed long-term potentiation, the strengthening of connections that underlies learning and memory.

The team then scaled up to the whole mouse brain, keeping it in a glass-like state for up to eight days. When thawed, hippocampal pathways again showed long-term potentiation. However, the researchers could not test whether actual memories had survived, because they could only measure activity in brain slices, not in a living animal.

The ultimate goal is human applications: preserving brain tissue after injury, establishing organ banks, and perhaps one day whole-body cryopreservation. But experts caution that scaling to human organs presents severe challenges, including heat transfer and cracking during rapid warming.

Questions 1-5

Choose the correct letter, A, B, C or D.

1. What is the main problem with freezing brain tissue? A. The tissue becomes too cold to thaw. B. Ice crystals damage cell structures. C. Neurons lose all water. D. The brain shrinks too quickly.

2. How does vitrification work? A. It freezes tissue slowly. B. It cools tissue so fast that ice crystals do not form. C. It removes all water. D. It uses heat to melt ice.

3. At what temperature were the brain slices rapidly cooled? A. Minus 150 C B. Minus 196 C C. Minus 40 C D. Minus 273 C

4. What is long-term potentiation? A. A type of ice crystal B. The strengthening of neural connections involved in learning C. A chemical antifreeze D. The freezing process

5. Why could the researchers not test whether memories survived? A. The mice died. B. They could only measure brain slices, not living animals. C. The hippocampus was destroyed. D. The antifreeze erased memories.

Questions 6-10

Do the following statements agree with the information? Write TRUE, FALSE or NOT GIVEN.

6. Individual brain cells can survive freezing.
7. The whole mouse brain was stored for up to eight days.
8. The method was first tested on human brains.
9. Scaling to human organs is straightforward.
10. The researchers used liquid nitrogen.

Questions 11-13

Complete the summary. Choose ONE WORD ONLY.

Vitrification cools tissue rapidly so water freezes into a 11 state instead of forming ice 12. After thawing, the hippocampus still showed long-term 13, essential for learning.

Answers

1. B 2. B 3. B 4. B 5. B
2. TRUE 7. TRUE 8. FALSE 9. FALSE 10. TRUE
3. glass-like 12. crystals 13. potentiation

Key Vocabulary

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