An Inserm research team in Toulouse, led by Dr Stein Silva (Inserm Unit 825 "Brain imaging and neurological handicaps"), working with the "Modelling tissue and nociceptive（疼痛的） stress" Host Team (MATN IFR 150), were interested in studying the illusions described by many patients under regional anaesthetic（麻醉剂） . In their work, to be published in the journal Anesthesiology, the researchers demonstrated that anaesthetising an arm affects brain activity and rapidly impairs¹ body perception. The ultimate aim of the work is to understand how neuronal circuits are reorganised at this exact moment in time and to take advantage of anaesthesia to reconfigure them correctly following trauma². This would allow anaesthetic techniques to be used in the future to treat pain described by amputated（截肢） patients in what are known as "phantom³（幽灵的，幻觉的） limbs".

Neuroscience research in recent years has shown that the brain is a dynamic structure. Phenomena⁴ such as learning, memorising or recovery from stroke are made possible by the brain's plastic properties. Brain plasticity does not, however, always have a beneficial effect.

For example, some amputated patients suffering from chronic⁵ pain (known as phantom limb pain) feel as though their missing limb were "still there". Such "phantom limb" illusions are related to the appearance in the brain of incorrect representations of the missing body part.

Persons under regional anaesthetic describe these very same false images.

Based on these observations, Inserm's researchers wished to discover whether anaesthesia could, in addition to fulfilling its primary function, induce（诱导，引诱） comparable phenomena in the brain. If this were so, anaesthetics could be used as new therapeutic⁶ tools capable of modulating⁷ brain activity.

With this in mind, a team headed by Dr Stein Silva monitored 20 patients who were to have one of their arms anaesthetised before surgery. The patients were shown 3D images of the hand, shot from different angles, and their ability to distinguish the right hand from the left was assessed. Results showed how anaesthesia affected⁸ the patients' ability to perceive their body correctly.