Anesthesia Affects the Mind's Perception of the Body

January 20, 2011

Researchers demonstrated that anaesthetizing an arm affects brain activity and rapidly impairs body perception.

Researchers demonstrated that anesthetizing an arm affects brain activity and rapidly impairs body perception.

The research was performed by 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 stress" Host Team. The researchers were interested in studying the illusions described by many patients under regional anesthetic. The research was published in the journal Anesthesiology.

The ultimate aim of the work is to understand how neuronal circuits are reorganized and to take advantage of anesthesia to reconfigure them correctly following trauma. This would allow anesthetic techniques to be used in the future to treat pain described by amputated patients in what are known as "phantom limbs."

Neuroscience research in recent years has shown that the brain is a dynamic structure. Phenomena such as learning, memorizing, 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 chronic 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 anesthetic describe these very same false images.

Based on these observations, Inserm's researchers wished to discover whether anesthesia could, in addition to fulfilling its primary function, induce comparable phenomena in the brain. If this were so, anesthetics could be used as new therapeutic tools capable of modulating brain activity.

With this in mind, a team headed by Dr Stein Silva monitored 20 patients who were to have one of their arms anaesthetized 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 anesthesia affected the patients' ability to perceive their body correctly.

The researchers observed three phenomena based on these tests:

-All the patients described false sensations in their arm (swelling, difference in size and shape, imagined posture).

-In general, patients under anesthesia took longer to distinguish between a left and right hand and made far more mistakes than persons not under anesthetic.

-The best results were obtained when the anaesthetized limb was visible.

In other words, anaesthetizing the hand (peripheral deafferentation ) modifies brain activity and rapidly changes the way we perceive the outside world and our own body. The teams are now using functional brain imaging to characterize the regions concerned in the brain. They also hope that it will be possible to use anesthesia for therapeutic purposes in the future by modulating post-lesional plasticity (chronic pain in amputated patients, improved recovery in those suffering from brain lesions).

Inserm researcher Silva, an anesthetist and the chief author of the study, believes that it will no doubt be necessary to develop new anesthetic techniques to inhibit or directly stimulate the brain images associated with painful phenomena.

Source: INSERM (Institut national de la santé et de la recherche médicale)--Is this consistent with your knowledge of anesthesia and its effects on the body?