Have scientists discovered why some people see ghosts?

A team of scientists thinks it may have solved one of humanity's great mysteries: why some people see ghosts.

Researchers conjured artificial apparitions during an experiment in Switzerland by mixing signals in participants' brains.

After undergoing the testing, volunteers reported a creepy "presence" behind them - counting up to four phantoms where no-one was.standing and reporting being touched by invisible fingers.

The robotic device which caused the sensation confuses people's perceptions of "self" and "other".

Researchers say the experiment suggests that "feelings of presence" - often believed to be ghosts or other frighterning figures - are really a figment of the imagination.

The officials from Ecole Polytechnique Federale de Lausanne (EPFL) say such experiences are often reported by people in extreme physical or emotional situations, or those suffering mental conditions that affect the brain - such as epilepsy, stroke or migraine.

The experiment used a slave robot device, which allowed volunteers to control the movements of one robotic arm in front of them using their index fingers.

Those movements were translated to a robotic arm behind them, which touched their backs.

When both occurred with a delay between the finger movements and the back-touching, the participants were given a sensation of of being watched and even touched by one or more ghostly presences.Upon being questioned, several reported a feeling of invisible people being close to them, while two of the 12 healthy participants were so disturbed that they asked for the experiment to be halted.

Before the experiment was conducted, brain scans were carried out on 12 patients with neurological disorders who had experienced "feelings of presence" before.

Disturbances were identified in three specific brain regions: the insular cortex, parietal-frontal cortex, and temporo-parietal cortex.

All of those are related to self-awareness, movement, and sense of position in space.