One month later, with her daughter Jin Jin, Li returns to Tian's office at the China-Japan Friendship Hospital in Beijing's Chaoyang district. The device was not switched on immediately after the surgery to give the brain time to recover from the minor wounds inflicted during surgery. That means Li's hands still shake, for the next few moments, at least.

After assessing data from her operation, and adjusting the settings of the implanted device accordingly via a remote control, Tian presses the power button.

Immediately, her hands stop shaking. Tian once again asks Li to write down her name, and her handwriting is close to perfect. Then the chopstick test is passed with flying colors as Li, with the adroitness of her youth, successfully picks up a small pill with the bamboo implements.

"It is a miracle!" Jin exclaims, with tears in her eyes, "a real medical miracle."

"Watching doctor Tian change the parameters of the device was just like watching him change the channel of a television. When he found the right channel, the miracle happened," Jin recalls.

After witnessing her hardship for the past 20 years, Jin was so excited to see her mother's steady hands working as they used to.

"At first, it was just one of her hands that started shaking, so she trained herself to use the other hand to eat. This disease developed slowly, but in the past three years, it gradually took over both of them, and then her head and, eventually, she could not eat by herself anymore," says Jin.

"My dad and I had to take turns to feed her each meal. My mom is tough, though, and she would not let us help her get dressed, even though it took her a long time to manage with the tremors in her hands," says Jin.

In Kunming, Yunnan province, Jin had consulted with many local hospitals and tried different medicines, but no doctor gave a confirmed diagnosis of her mother's condition, which gradually worsened.

In April, Jin's sister saw an online video of Tian performing brain surgery on a 69-year-old man from Dezhou, Shandong province, curing his shaking hands. She immediately forwarded the video to Jin. It was clear then that Tian was Li's best hope of a rescue from the grip of this debilitating illness.

Associate chief physician at the neurosurgery department of the China-Japan Friendship Hospital, Tian specializes in diagnosing and treating epilepsy, Parkinson's disease and essential tremor.