Shuen Chun-wa, 81, and her husband rushed to a green bus along with 20 other Hong Kong residents, dragging empty suitcases. They had purple tour stickers on their jackets and were heading shopping in Shenzhen, a bustling Chinese city north of the border with Hong Kong.

It was Ms. Shuen's second trip to Shenzhen to find bargains in a year. The last time she got dental implants. “You can count how much I have to pay,” she said. She paid $9,000 in Shenzhen for a procedure that would have cost $25,000 in Hong Kong. 'I don't have the money. So I went to Shenzen.”

Since China opened its borders in January 2023 after several years of pandemic isolation, Hong Kong residents have made Shenzhen a weekend destination for shopping, dining and, yes, even the dentist.

Fed up with high costs, poor service and limited choice at home, Hong Kongers are heading to Shenzhen to shop for groceries, eat out and discover new bubble tea shops. Hong Kong remains one of the most unaffordable cities in the world, and its battered economy and plummeting stock market have made everyone more money-conscious. In China, a stagnant economy has led to a steady decline in prices, which have fallen the most since the 2009 global financial crisis and are bordering on a phenomenon known as deflation.

The retail migration is a reversal of the days when mainland Chinese flocked to Hong Kong to buy everything from luxury bags to baby food. For Hong Kongers, the slowdown in China offers a rare price drop. All it takes is a short bus or metro ride across the border to the mainland.

On social media and chat groups, hundreds of thousands of Hong Kongers are talking about new food offerings in Shenzhen, such as pastries filled with seaweed and pork floss. They share tips on where to find bubble tea, including a place where the tea is brewed by a robot. Tour operators that once focused on package holidays to Japan and Thailand are now also organizing buses to shopping centers in Shenzhen to visit stores such as Sam's Club.

Some weekends there are so many Hong Kongers in Shenzhen's malls that locals joke that the visitors are 'occupying' them.

Their presence in Shenzhen, a city of 17 million inhabitants, is visible everywhere. Some stores are adapting their advertisements by using Cantonese, Hong Kong's local Chinese language, to attract tourists to their stores. Restaurants offer discounts to customers with phone numbers that include Hong Kong area code 852. In a large shopping center near a border crossing, opticians and dental clinics promise a cheaper service than Hong Kong, requiring only a short journey. “Cross the border to check your teeth without any distance,” enticed a giant neon pink ad.

On a busy day, the GoodFeel Dentist clinic could see more than 100 customers from Hong Kong, said Lan Xinghua, a sales director at GoodFeel Dentist. He said the company's turnover doubled when the border with Hong Kong opened last year. To generate even more sales, the clinic set up a stall near the border crossing at Luohu Port. Employees are expected to speak both Cantonese and Mandarin, the official language of China.

“Hong Kong customers spend more money and generally don't bargain too much,” Mr Lan said. Sometimes entire families come to have their teeth cleaned and repaired.

The two cities are separated by a border that distinguishes mainland China from Hong Kong, a Chinese territory that long operated with a degree of autonomy but has increasingly come under Beijing's rule.

Many Hong Kongers who traveled to the mainland for shopping had not been there since 2019. Then pro-democracy protests swept Hong Kong and the government responded with a crackdown, eradicating the political tolerance that had distinguished Hong Kong from mainland China.

Now people in Hong Kong, using online forums that are censored or inaccessible on the mainland, are discussing whether it is safe and politically acceptable for people who disagree with the Chinese government to visit Shenzhen, even just to shop and to dine.

For many, the answer is 'yes'.

“Life and political opinion can be separated,” said Chak Yeung, 31, a Hong Kong resident who works in the technology industry. He has been involved in student organizations participating in protests in the past, but he doesn't see any conflict between his political views and what he does for fun on the weekends.

Hong Kong has a separate currency from that of China, and its merchants still rely heavily on cash for payments. The main form of payment in China is digital: the two main payment apps, WeChat and Alipay, have only recently become available to Hong Kongers and not everyone is familiar with them. To help visiting shoppers, posters in Shenzhen's stores and subway stations explain how Hong Kong residents can use WeChat and Alipay. Tourists can also pay in Hong Kong dollars and not convert their money into Chinese renminbi.

But paying is not always smooth. On her most recent trip, Ms. Shuen used cash to buy dandelions that her son uses in his Chinese medicine practice in Hong Kong, as well as some dried shrimp. But she said paying in cash was difficult.

Exploring Shenzhen can also be difficult. Two women from Hong Kong had to ask a Shenzhen resident, Kristen Lu, 28, how to use local navigation apps on their phones. They didn't realize that Google Maps doesn't work in mainland China because the company is blocked.

Mr. Yeung, the technical assistant, has visited Shenzhen twice in the past year. He enjoys eating hot pot and playing archery and basketball in a sports and entertainment complex. He said the workers he encounters in Shenzhen are more pleasant.

The service in Hong Kong is grimmer and more hasty, he said.

For Iris Yiu, 29, a student pursuing a master's degree in Hong Kong, going to Shenzhen is all about food. She said she is a fan of spicy food, a staple in parts of southern China, and in November she and two friends went to Shenzhen and ordered “crazy” from a famous Sichuan food chain called Taier Sauerkraut Fish. They weren't ready yet. Next they stopped at Bobo Chicken, a restaurant that serves vegetables and meat in small bites on sticks that cost 14 cents each.

Ms Yiu said local customers stared at them as they grabbed as many sticks as they could. Someone at a nearby table said, “This is the style of Hong Kong people, as if they don't need money!”

Snow Wong, 28, heard about Shenzhen when her friends and colleagues returned from weekend trips. After so many rave reviews, Ms. Wong decided to try it herself.

She visited arcades and karaoke bars and discovered that the city had more interesting escape room games, her favorite pastime, than Hong Kong. She used Hong Kong dollars to pay for a visit to a spa near the Luohu border crossing.

Above all, Ms. Snow said, Shenzhen offered something that Hong Kong famously lacks: a slower pace.

“The pace of Shenzhen and Hong Kong is so different,” Ms Wong said. “Shenzhen is the place where I go to relax.”

Traumatic brain injuries leave more than five million Americans permanently disabled. They have difficulty concentrating on even simple tasks and often have to quit their jobs or drop out of school.

A study published on Monday has offered them a glimpse of hope. Five people with moderate to severe brain damage had electrodes implanted in their heads. As the electrodes stimulated their brains, their performance on cognitive tests improved.

If the results hold up in larger clinical trials, the implants could become the first effective therapy for chronic brain injury, the researchers said.

“This is the first evidence that you can switch the dial on this problem,” says Dr. Nicholas Schiff, a neurologist at Weill Cornell Medicine in New York who led the study.

Gina Arata, one of the volunteers who received the implant, was 22 when a car accident left her with fatigue, memory problems and uncontrollable emotions. She abandoned her plans for law school and lived with her parents in Modesto, California, where she was unable to hold down a job.

In 2018, 18 years after the crash, Ms Arata received the implant. Her life has changed dramatically, she says. “I can be a normal person and have a conversation,” she said. “It’s amazing how I’ve seen myself improve.”

Dr. Schiff and his colleagues designed the test based on years of research into the structure of the brain. Those studies suggested that our ability to focus on tasks depends on a network of brain areas connected by long branches of neurons. The regions send signals to each other, creating a feedback loop that keeps the entire network active.

Sudden movements of the brain – for example in a car accident or a fall – can sever some long-distance connections in the network and cause people to fall into a coma, Dr. hypothesizes. Schiff and his colleagues. During recovery, the network may be able to power itself again. But if the brain is severely damaged, it may not recover completely.

Dr. Schiff and his colleagues have identified a structure deep in the brain as a crucial node in the network. Known as the central lateral nucleus, it is a thin layer of neurons the size and shape of an almond shell.

The human brain has two such structures, one in each hemisphere. They seem to help the brain calm itself at night for sleep and restart the brain in the morning. Stimulating the neurons in these regions can wake a sleeping ratDr.’s research has shown that Schiff demonstrated.

These studies raised the possibility that stimulating the central lateral nuclei could help people with traumatic brain injuries regain focus and attention.

Surgeons regularly implant electrodes in patients with Parkinson’s disease. The little electrical pulsesreleased by the implants hundreds of times per second commands neighboring neurons to fire their own signals, restoring some brain functions.

In 2018, Dr. Schiff and his colleagues recruited volunteers like Ms. Arata, who suffered from chronic problems for years after their accident. Before inserting the electrodes, the researchers gave the volunteers a series of tests to assess their ability to concentrate and switch tasks. For example, in one exam, the volunteers were each given a sheet of paper full of letters and numbers and had to draw a line connecting them as quickly as possible.

Before the surgery, the researchers scanned each volunteer’s brain to create an accurate map. Dr. Jaime Henderson, a neurosurgeon at Stanford University, guided the electrode through the brain to the central lateral nucleus.

Dr. Henderson implanted the electrodes in six volunteers, but one of them had to stop the study after developing a scalp infection. Starting one month after surgery, the remaining five volunteers underwent follow-up testing. On the letters and numbers exam, their scores rose anywhere from 15 to 52 percent.

To gain a broader understanding of the volunteers’ experiences, Dr. Joseph Fins, a medical ethicist at Weill Cornell Medicine, conducted a study series of interviews with them and their family members. Most volunteers, like Ms. Arata, said the implant made them look more like their former selves.

In contrast, the volunteer who saw the greatest improvement on cognitive tests responded tepidly. “I don’t think it hurts,” he said. “I just don’t know if it helped much.”

And yet that patient’s son observed significant changes, especially in his father’s self-awareness. “It is day and night,” said the son.

Dr. Steven Laureys, a neurologist at the University of Liege in Belgium who was not involved in the study, said the results supported the theory that attention and other forms of thinking depend on the brain-wide network. “There’s plenty of reason to believe it’s worth pursuing,” he said of the study.

Dr. Schiff and his colleagues are planning a much larger study of brain implants. “We’ll have to see how the data shakes out,” he said.

The central lateral nuclei are not the only regions that show promise as nodes in the brain network, said Dr. Alex Green, a neurosurgeon at the University of Oxford who was not involved in the study.

“We don’t really know yet what the best place to stimulate is,” said Dr. Green. He and his colleagues are preparing a brain injury study of their own to try electrodes in an area called the pedunculopontine nucleus.

Dr. Laureys acknowledged that implant surgeries would be expensive, but argued that society should recognize the millions of people who suffer from traumatic brain injuries. “This is a silent epidemic,” he said.

Gert-Jan Oskam was living in China in 2011 when he had a motorcycle accident that left him paralyzed from the hips down. Now scientists have given him back control of his lower body with a combination of devices.

“For 12 years I’ve been trying to get back on my feet,” said Mr. Oskam in a press briefing Tuesday. “Now I’ve learned how to walk normally, naturally.”

In a study Published Wednesday in the journal Nature, researchers in Switzerland described implants that formed a “digital bridge” between Mr Oskam’s brain and his spinal cord, bypassing injured parts. The discovery allowed Mr Oskam, 40, to stand, walk and climb a steep incline with only the aid of a walker. More than a year after the implant was inserted, he has retained these abilities and has actually shown signs of neurological recovery, walking with crutches even with the implant disabled.

“We captured Gert-Jan’s thoughts and translated those thoughts into spinal cord stimulation to restore voluntary movement,” Grégoire Courtine, a spinal cord specialist at the Swiss Federal Institute of Technology, Lausanne, who helped lead the research, said. during the press conference.

Jocelyne Bloch, a neuroscientist at the University of Lausanne who placed the implant in Mr Oskam added: “It was quite science fiction to me at first, but today it became true.”

There have been a number of advances in the technological treatment of spinal cord injury in recent decades. In 2016, a group of scientists led by Dr. Courtine managed to restore the ability to walk in paralyzed monkeys, and another group helped a man regain control of his crippled hand. In 2018, another group of scientists, also led by Dr. Courtine, a way to do this stimulate the brain with electrical pulse generators, enabling partially paralyzed people to walk and cycle again. Last year, more advanced Brain stimulation procedures allowed paralyzed subjects to swim, walk, and cycle within one day of treatment.

Mr. Oskam had undergone stimulation procedures in previous years and was even able to walk somewhat again, but eventually his improvement leveled off. During the press conference, Mr. Oskam said that these stimulation technologies had made him feel like there was something strange about his motor skills, a strange distance between his body and mind.

The new interface changed this, he said, “The stimulation used to control me, and now I control the stimulation.”

In the new study, the brain-spine interface, as the researchers called it, took advantage of an artificial intelligence thought-decoder to read Mr. Oskam’s intentions — detectable as electrical signals in his brain — and link them to muscle movements. The etiology of natural movement, from thought to intention to action, was preserved. The only addition, as Dr. Courtine described it was the digital bridge over the injured parts of the spine.

Andrew Jackson, a neuroscientist at Newcastle University who was not involved in the research, said: “It raises interesting questions about autonomy and the source of commands. You keep blurring the philosophical line between what the brain is and what the technology is .”

Dr. Jackson added that scientists in the field have theorized about connecting the brain to spinal cord stimulators for decades, but that this was the first time they had achieved such success in a human patient. “It’s easy to say, it’s much harder to do,” he said.

To achieve this result, the researchers first implanted electrodes in Mr. Oskam’s skull and spine. The team then used a machine learning program to observe which parts of the brain lit up as he tried to move different parts of his body. This thought decoder was able to match the activity of certain electrodes with certain intentions: one configuration lit up when Mr. Oskam tried to move his ankles, another when he tried to move his hips.

Then the researchers used a different algorithm to connect the brain implant to the spinal cord implant, which was set up to send electrical signals to different parts of his body, causing movement. The algorithm was able to account for small variations in the direction and speed of each muscle contraction and relaxation. And because the signals between the brain and spine were sent every 300 milliseconds, Mr. Oskam was able to quickly adjust his strategy based on what worked and what didn’t. Within the first treatment session, he was able to twist his hip muscles.

Over the next few months, the researchers refined the brain-spine interface to better suit basic actions like walking and standing. Mr. Oskam regained a somewhat healthy-looking gait and was able to negotiate stairs and ramps with relative ease, even after months without treatment. In addition, after a year of treatment, he began to notice marked improvements in his movement without the aid of the brain-spine interface. The researchers documented these improvements in weight-bearing, balance, and gait tests.

Now Mr. Oskam can walk around his house with restrictions, get in and out of a car, and stand at a bar for a drink. For the first time, he said, he feels like he’s in control.

The researchers acknowledged limitations in their work. Subtle intentions in the brain are hard to discern, and while the current brain-spine interface is suitable for walking, the same probably can’t be said for restoring upper body movement. The treatment is also invasive, requiring multiple surgeries and hours of physical therapy. The current system does not resolve all spinal cord paralysis.

But the team was hopeful that further progress would make treatment more accessible and systematically more effective. “This is our real goal,” said Dr. Courtine, “to make this technology available around the world to all patients who need it.”