Our memories may persist even when half of the brain connections that store them are wiped out, according to a study in dormant mice. The “remarkable” discovery tells us more about how memory works and could one day reveal ways to improve it.

“Memories may be harder to break than we thought,” says at Boston University, who wasn’t involved in the study. “This absolutely, substantially advances our understanding of how memory works.”

When we experience a stimulus, neurons in our sensory organs, like our eyes, transmit electrical signals to our brain. Neurons then process this information by firing electrical signals to each other via junctions called synapses.

These neurons, called engram neurons, encode information into a memory by forming new synapses and strengthening existing ones. Recalling a memory .

Many scientists think a memory persists as long as the specific pattern of synapses on the engram neurons encoding that memory is maintained. This is partly based on experiments that have used drugs or genetic tools to , says at the Okinawa Institute of Science and Technology in Japan.

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But recent studies suggest a memory persists in location or number. This has called into question “what’s necessary and sufficient to have a memory preserved”, says at Yale University.

To address this, Tanaka and his colleagues took inspiration from hibernating animals. “Under hibernation, brain activity seems to drop significantly,” he says. “But studies in natural hibernators show that somehow those animals, after arousal in the spring, seem to remember their friends and the location of food they hid before hibernation.”

By examining how memory is retained during hibernation, a situation in which the brain changes dramatically, the researchers hoped to unpick basic principles by which the mammalian brain stores memories long term. “The [researchers] very cleverly and creatively get at the question of memory by using hibernation as a way to poke and prod at the brain,” says Ramirez.

They applied weak electric shocks to the feet of mice – which don’t naturally hibernate – while they were in a chamber that smelled of alcohol, creating a fearful memory associated with that scent. The next day, the mice froze in fear upon being placed in the same chamber, without receiving shocks.

The researchers induced an artificial state of hibernation in about half the mice for two days. This was done by injecting them with drugs that slow metabolism and placing them in a dark chamber.

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Five days later, mice that had artificially hibernated still froze when placed in the alcohol-smelling chamber. This was despite brain scans revealing that more than half of the synapses within the engram neurons in their hippocampus – a brain region crucial for memory – disappeared during hibernation. “Despite massive brain remodelling during hibernation, the memories were retained,” says Tanaka.

Dragoi says the findings are relevant to people, since prior research has shown that our brains store information very similarly to mice. “It tells us something about how our mammalian brains may work,” says Ramirez.

The team also found that the hibernating rodents’ brains retained synapses that clustered closely together on the surface of engram neurons, while those outside these clusters disappeared. This suggests that clustered synapses specifically are crucial for retaining memory in the brain, says Tanaka.

Non-clustered synapses that were wiped out by hibernation reappeared within a day post-hibernation, indicating that, while clustered engram synapses are necessary to retain the information within memories, the non-clustered synapses may be important for accessing memories, he says.

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“This study is a remarkable step forward because it addresses a long-standing puzzle in memory research: how the brain retains long-term memories,” says at Vrije University Amsterdam in the Netherlands.

The team is exploring the molecular pathways through which clustered engram synapses store information and plans to dig into how non-clustered ones reappear, says Tanaka.

Targeting such pathways with drugs could even reveal ways to prevent or slow memory impairment, says Ramirez. “It gives hope that even in instances where information seems to be lost in the brain, whether it’s amnesia or Alzheimer’s disease, memory may nonetheless persist.”

Like many people, I spend much of my time at home fantasising about my next holiday. During the trip itself, most of my stresses seem to melt away, and I return feeling optimistic and energised.

Each time, I am determined to integrate those feelings into my day-to-day life, but I am almost invariably disappointed. Within a couple of weeks – sometimes less, depending on how much time I have to spend on the London Underground – I become the same irritable and frustrated person that I always was. And so, I start dreaming about my next escape.

As I planned a recent trip to Madrid, I wondered whether I was foolish to hope that my travels would offer anything more than temporary relief.

Delving into the psychological literature, though, I was relieved to see that the answer is a resounding no. Growing evidence explains the specific ways that our holidays can increase our wellbeing and, crucially, the types of activities that will offer the greatest restoration, based on the ancient Greek principle of eudaimonia: “human flourishing”.

“Instead of thinking only about where you are going to travel, you can think about what psychological experience you want the vacation to provide, and try to create that experience,” says , a psychologist at the University of Amsterdam in the Netherlands.

A serious consideration of holiday psychology has been a long time coming: until recently, psychologists studying wellbeing had mostly focused on the benefits of relaxation and leisure activities more generally. There have been plenty of , for instance, while the research on vacations was patchy. As a result, they failed to capture the distinct opportunities for a mental reset that holidays can afford away from the daily grind. “From a psychological perspective, that separation is quite important,” says Yan.

��DzԲ���������, published last year. Analysing the results of 32 different studies,  at the University of Georgia has shown that the average mood boost begins before we have even left home, as the anticipation of a trip builds. Those good feelings remain highly elevated for at least 21 days after we have returned home and may not return to the baseline for a further three weeks.

If you, like me, struggle to feel those longer-lasting benefits, it may be because you have been focusing on the “wrong” kind of happiness. Behavioural scientist at the University of St Andrews Business School in the UK argues that we should distinguish between hedonic wellbeing, which concerns enjoyment and pleasure, and eudaimonic wellbeing, which concerns “personal growth, sense of purpose and meaning”.

“On holiday, hedonic wellbeing might come from lounging on a beach, enjoying nice food or staying in a lovely hotel,” he says. “Eudaimonic wellbeing might come from the sense of achievement in completing a challenging hike, learning about a new culture or forming connections with fellow travellers.”

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, McLean and his colleague at King Faisal University in Saudi Arabia found that the boost in hedonic wellbeing faded pretty quickly, whereas the eudaimonic feelings lingered for at least eight weeks. For this reason, he recommends planning holidays that combine both elements – pure relaxation alongside the kinds of activities that feel more purposeful.

Yan agrees. “Travel can also expose people to novelty, different cultures, new activities and different versions of themselves,” she says – and it is here that the biggest benefits lie. “These experiences may help people not only feel rested, but also feel more alive, connected and reflective.”

So, what can we do to achieve it? Based on the available research on both hedonic and eudaimonic wellbeing,  to think about (see below).

You don’t have to include every single element, but you may benefit from reflecting on the list and deciding which are most significant to you. “For example, if relatedness is very important, you might want to prioritise meaningful time with family, friends or a partner, rather than trying to do too many activities,” says Yan. To maximise autonomy, “it helps to build in freedom and flexibility”, she says. “A vacation that is too tightly scheduled can become another source of pressure.”

Mastery, meanwhile, might involve attending an art class or learning to scuba dive, and the need for novelty might encourage you to try to experience a whole new culture, rather than returning to a familiar destination.

That may take more serious attention than you currently pay to your travel plans. “Do not treat vacations only as time off. Think about what kind of psychological needs the vacation can satisfy,” says Yan. The hard work may pay off immediately. “Our research showed that merely anticipating an upcoming vacation can boost wellbeing, so the planning and looking-forward phase has value in itself,” says McLean. “It’s better to book early!”

If you are worried about protecting your purse strings, rest assured that you can glean many of these benefits from shorter trips – in fact, the . Nor do the activities have to be exceptionally luxurious: in Grant’s meta-analysis, physical exercise proved to be one of the best predictors of enhanced wellbeing, and that can be achieved through long walks or visits to outdoor gyms.

You may not even have to leave your home city, provided that you take those psychological needs seriously enough and don’t simply spend the time catching up on other responsibilities. When planned correctly, taking some time off at home can still be beneficial, says Yan. “For example, people can create boundaries around work, avoid routine chores during the holiday period, try new local activities, spend quality time with others, visit nearby nature or create small rituals that make the time feel different from ordinary life.”

Whether you are travelling abroad or staying at home, you should try to find ways to immerse yourself in the memories of the experiences after your break has ended. Along these lines, McLean also found that using virtual-reality headsets to return to the location of their holidays significantly prolonged the wellbeing benefits experienced by his study participants.

We can’t all afford this technology, of course, but he suggests some lo-fi alternatives. “Deeply engaging with holiday memories – perhaps through journaling about the experience in vivid detail, creating a rich photo or video montage that you actively revisit, or even planning a return trip to the same destination – might tap into similar psychological pathways, though this would need further research to be confirmed.”

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“The underlying factor is about re-engaging psychologically with the vacation experience in a rich, immersive way,” says McLean. You are unlikely to get this from passively scrolling through your photos; it needs your full attention.

Attempting to put all this into practice on my trip to Madrid, I made a greater effort to chat to locals in Spanish, maximising my sense of autonomy and mastery; attended a concert by one of my favourite singers, an experience that was imbued with meaning; and visited the city’s botanical gardens, which helped me connect to nature.

It has now been six weeks since I returned, and the warm glow remains. My sunnier mood may be slowly fading, but it hasn’t yet been extinguished. Now, I’m dreaming of my next trip.

A man who became paralysed after a diving accident six years ago regained the ability to move and feel pressure in his hands thanks to brain stimulation. Now, researchers have revealed he maintained this ability for months after the stimulation was turned off. This suggests the intervention has caused a rerouting of his neuronal connections through neuroplasticity.

“We turned everything off completely, for many months, and yet he’s maintained these gains,” says at the Feinstein Institutes for Medical Research in New York. “That’s unheard of.”

Keith Thomas, 48, was paralysed from the chest down in July 2020. He had no sensation or control over his limbs and had significant muscle wasting, says Bouton.

In 2023, Bouton and his colleagues performed a double neural bypass surgery on Thomas, placing five electrodes into his brain in regions associated with arm movements and feeling. They then connected computer cables to these electrodes, so artificial intelligence could interpret his movement intentions. That information was then wired into electronic splints that stimulated his arms, hands and fingers to carry out his intended movements, enabling him to pick up coffee cups and scratch his face.

To recreate the sense of feeling, the team embedded force sensors into 3D-printed wearable devices for Thomas’s hands and fingers, which sent feedback via electrical stimulation into the brain’s sensory areas.

After conducting a series of experiments – which even involved Thomas feeling objects through another person’s hand – Bouton says the team planned to stop the stimulation for about a month, to test for any lingering effects. “Then we had a fire in the building, and it actually forced us to stop stimulation for even longer than we’d planned, for about three months.”

The unexpected interruption led to surprising findings: Thomas continued to maintain strength, feeling and function in his hands. “He’s now also controlling individual fingers with even more accuracy, so that’s big,” says Bouton.

In a video interview with New Ů��С��Ƶ, Thomas raised his elbows nearly to shoulder level and described feeling “tingling” in his wrist in response to pressure, even when he’s “unplugged from the computer”. “When I first felt it, it was amazing,” he says. “I’m used to it now.”

 at the University of California, Davis, says the work suggests that this approach promotes lasting recovery of the nervous system. “The goal is to help the nervous system partially heal so the person can move their own body better,” he says.

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“If these improvements persist even when the system is turned off, then the device is doing more than temporarily restoring function,” says at the University of California, Los Angeles. “It may be helping the nervous system reorganise itself through neuroplasticity.”

This describes the brain’s ability to rewire itself by forming new neural connections, such as or even . “After an injury such as spinal cord injury, those same mechanisms may help restore function by strengthening spared pathways or recruiting alternative circuits, allowing neural signals to travel through networks that were previously too weak to support meaningful movement,” says Lu.

The researchers have observed stronger neural responses in Thomas’s sensory cortex since the intervention.

But this is just a single case report, so it’s unclear how well this approach would work on other people with paralysis from different types of injuries. at the University of Chicago says he has spent years working on stimulation and continues to find that some respond better than others, and some not at all. “And we have no idea why,” he says. “So, the question is: can you replicate it? This is a really ambitious study, but we need to see them replicating their results in more participants before we believe the hype.”

As to Thomas’s future, “at this point now we know nothing’s impossible, or anything’s possible”, says Boulton. “I think it’s possible he will continue to to improve,” he adds.