7- out-of-body experience? your brain is to blame
They are eerie sensations, more common than one might think: A man describes the distinct feeling of a shadowy figure standing behind him, and then turns around to find no one there. A woman feels herself leaving her body and floating in space, looking down on her physical body.
People often attribute such experiences to paranormal forces outside the sphere of material life. But according to recent work by neuroscientists, they can be induced by delivering mild electric current to specific spots in the brain.
In one woman, for example, a zap to a brain region—the angular gyrus— resulted in a sensation that she was hanging from the ceiling, looking down at her body. In another woman, electrical current delivered to the same area triggered a feeling that someone was behind her, intent on interfering with her actions.
The two women were being evaluated for epilepsy surgery at University Hospital in Geneva, Switzerland. Doctors implanted electrodes into their brains to find the abnormal tissue causing their seizures. As each electrode was activated, stimulating a different patch of brain tissue, the patient was asked to say what she was experiencing.
Dr. Olaf Blanke, who carried out the procedures, is a neurologist at the Ecole Polytechnique F6d6rale de Lausanne in Switzerland. He said that the women had normal psychiatric histories and that they were stunned by the bizarre nature of their experiences.
But this is not a film scenario, and there is nothing mystical about these ghostly experiences, said Peter Brugger, a neuroscientist at University Hospital in Zurich. Dr. Brugger is an expert on phantom limbs—the sensation of still feeling a limb that has been amputated.
"The research shows that the self can be detached from the body and can live a phantom existence on its own, as in an out-of-body experience. It can also be felt outside of personal space, as in a sense of a presence," Dr. Brugger said.
Scientists have gained new understanding of these odd bodily sensations as they have learned more about how the brain works, Dr. Blanke said. For example, researchers have discovered that some areas of the brain combine information from several senses. Vision, hearing, and touch are Initially processed in the primary sensory regions (eyes, ears, fingertips, etc). But then they flow together, like smaller streams flowing into a river, to create the wholeness of a person's perceptions. For example, a dog is visually recognized far more quickly if it is simultaneously accompanied by the sound of its bark.
These multisensory processing regions also build up perceptions of the body as it moves through the world, Dr. Blanke said. Nerves in the body act as sensors. Sensors in the skin provide information about pressure, pain, heat, cold, and similar sensations. Sensors in the joints, tendons, and bones tell the brain where the body is positioned in space. Sensors in the ears track the sense of balance. And sensors in the Internal organs, including the heart, liver, and intestines, provide an assessment of a person's emotional state.
Real-time information from the body, the space around the body. and the subjective feelings from the body are also represented in multisensory regions, Dr. Blanke said. And if these regions are directly stimulated by an electric current, as in the cases of the two women he studied, the Integrity of the sense of body can be altered.
As an example, Dr. Blanke described the case of a 22-year-old student who had electrodes implanted into the left hemisphere of her brain in 2004.
"We were checking language areas," Dr. Blanke said. The woman suddenly turned her head to the right. That made no sense, he said, because the electrode was nowhere near areas involved in the control of movement. Instead, the current was stimulating the angular gyrus, which blends vision with body sense.
Dr. Blanke applied the current again. Again, the woman turned her head to the right. "Why are you doing this?" he asked. The woman replied that she had a weird sensation that another person was lying beneath her on the bed. The figure, she said, felt like a "shadow" that did not speak or move; it was young, more like a man than a woman, and it wanted to interfere with her.
When Dr. Blanke turned off the current, the woman stopped looking to the right, and said the strange presence had gone away. Each time he reapplied the current, she once again turned her head to try to see the shadow figure.
When the woman sat up, leaned forward and hugged her knees, she said that she felt as if the shadow man was also sitting and that he was clasping her in his arms. She said it felt unpleasant. When she held a card in her right hand, she reported that the shadow figure tried to take it from her. "He doesn't want me to read," she said.
Because the presence closely simulated the patient's body posture and position, Dr. Blanke concluded that the patient was experiencing an unusual perception of her own body, as a double. But for reasons that scientists have not been able to explain, he said, she did not recognize that it was her own body she was sensing.
This impression of a mimicking, shadowy self-simulation can occur without electrical stimulation to the brain, Dr. Brugger said. It has been described by people who undergo sensory deprivation, as in mountaineers trekking at high altitude or sailors crossing the ocean alone. It is also experienced by people who have suffered minor strokes or other disruptions in blood flow to the brain.
Six years ago, another of Dr. Blanke's patients underwent brain stimulation to the angular gyrus. The patient experienced a complete out-of-body experience.
When the current flowed, she said: "I am at the ceiling. I am looking down at my legs."
When the current ceased, she said: "I'm back on the table now. What happened?"
Because the woman's felt position in space and her actual position in space did not match, her mind searched for the best way to turn her confusion into a coherent experience, Dr. Blanke said. She concluded that she must be floating up and away while looking downward.
Some schizophrenics, Dr. Blanke said, experience paranoid delusions and the sense that someone is following them. They also sometimes confuse their own actions with the actions of other people. While the cause of these symptoms is not known, he said, multisensory processing areas may be involved.
When otherwise normal people experience bodily delusions, Dr. Blanke said, they are often completely confused. The felt sensation of the body is so real, so familiar, that people do not realize it is a creation of the brain.
Yet the sense of body integrity is rather easily tricked, Dr. Blanke said. While it may be tempting to credit the supernatural when this body sense goes wrong, the true explanation is a very natural one. It is the brain's attempt to make sense of conflicting information.
