A man in a permanent vegetative state (PVS) for the past 15 years has shown signs of consciousness after pioneering nerve stimulation treatment.

The 35-year-old was left apparently unaware of the world around him following a car accident in 2001, but is now responding to questions a month after having a stimulator placed on a nerve which connects the heart, lungs and digestive tract to the brain.

The treatment is challenging the commonly accepted view that there is little prospect of a recovery if a patient has been in PVS for more than a year.

As well as responding to simple requests such as turning his head, the patient could track objects with his eyes and stay awake while being read a story.

He even attempted to smile when asked and had tears in his eyes when played music by his favourite French singer Jean-Jaques Goldman, reports the New Scientist.

Angela Sirigu, who led the work at the Institut des Sciences Cognitives Marc Jeannerod in Lyon, told the magazine her team were “very happy” when he started to react.

“This patient is like our baby. We are very attached to him. He’ll always remain in our hearts, because he’s our first patient,” she said.

The results show “it is possible to improve a patient's presence in the world,” she added in a statement.

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The vagus nerve is linked to two regions in the brain which play key roles in alertness and consciousness. It also runs down both sides of the neck from the brain stem, across the chest and into the abdomen.

During a 20-minute procedure, a small implant was placed on the nerve in the man’s neck, resulting in what doctors describe as a state of minimal consciousness.

Ms Sirigu and her team now hope to apply the technique more widely to patients with less serious brain injuries, where the gains could be even greater.

The findings offer hope to families of victims in PVS that they could one day re-establish meaningful contact.

Niels Birbaumer, a pioneering brain surgeon at the University of Tübingen, told The Guardian the findings raised new ethical dilemmas.

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“Many of these patients may and will have been neglected, and passive euthanasia may happen often in a vegetative state,” he said. “This paper is a warning to all those believing that this state is hopeless after a year.”

The man is unlikely ever to walk or talk again due to the extensive damage to his brain, which might lead some to question whether patients would want to even be made aware of their condition.

“Personally I think it’s better to be aware, even if it’s a bad state, to be conscious of what’s happening,” Ms Sirigu said. “Then you can have a decision if you want to go on or if you want [euthanasia].”