Olaf Blanke, École Polytechnique in Lausanne
Do you ever get that feeling that there's someone just behind you, even though there isn't? Well, now a team of scientists think they've found a way to provoke that feeling merely by stimulating a particular part of the brain called the temporal parietal junction. This is all coming from an investigation of a 22-year-old woman who was originally being evaluated for surgical treatment of epilepsy. But, during this, the researchers found they were able to do something very different. Explaining all to Chris Smith was Olaf Blanke from the École Polytechnique in Lausanne.
Olaf Blanke: What we basically have the chance to investigate in this patient is something that many clinicians and probably cognitive neuroscientists would also like to do, mainly induce by a very focal stimulation of one specific part of the brain, the temporal parietal junction, a highly complex experience. What we, in short, and could induce was that she had the experience that all of a sudden, during the two seconds of stimulation, that there was another person in the room and that this person was always localised behind her, very specific distance, just behind her to her right. And this experience was so convincing that she actually had to turn around and look in order to make sure that there was actually nobody there.
Chris Smith: So when we get the sensation that there's someone literally standing behind you making the hairs on the back of your neck stand up, if you like, then we can be reasonably sure from the results you've found that it's this part of the brain that's responsible?
Olaf Blanke: So basically what this shows is that there is at least one anatomical mechanism that seems to be very strongly involved in generating these sensations and, although it's a highly complex phenomenon that you can find in schizophrenic patients but also in healthy subjects, it seems to be due to disturbed brain mechanisms exactly at this area.
Chris Smith: Is it significant that it's on the left? Because does the person see the apparition, if you like, or feel the presence of the apparition on the contralateral, the opposite side of the body, because you're stimulating the left? And if you were to do it on the right, would you get the converse effect?
Olaf Blanke: Yes, exactly. That can actually be suspected because there have been reports before, this feeling of a presence is always contralateral, on the other side, with respect to the side of the brain where there might be a disturbance, a lesion or other kind of brain damage. So if you have your left temporal parietal junction involved it will be on the right side and when you have your right brain involved it will be on the left side.
Chris Smith: So what do you think the actual role of this piece of the brain is when it's working normally?
Olaf Blanke: Actually we have observed it in the induction of similar illusions as well. To give you an example would be an out of body experience: it's the same area that's relevant. There's also doppelganger experience where you have the impression of seeing an image of yourself outside, out of space. So all these experiences somehow seem to be generated by stimulation or interference with this temporal parietal junction.
Chris Smith: It's really interesting as well because one of the things which is very striking about a number of psychiatric illnesses, especially schizophrenia, is that people experience sensations that are obviously coming from within their own brain but they always say they're coming from outside. So is there any evidence to suggest that, again, this part of the brain might be involved in causing that?
Olaf Blanke: Absolutely. So we believe that there is a disturbance of so-called self other distinction, namely what we could show was that when we changed the position of the patient those changes were echoed in the posture and position of the illusory person. Nevertheless, she never experienced that person as reflecting her own body or being illusion related to her own body. And this is similar to patients with schizophrenia, for example. So, for example, you ask them to grasp, let's say, a glass of water and while they perform this action they could tell you that they have the experience as if somebody else were directing their arm. So what our patient has, not for a certain action, not for a certain body part, is a similar disturbance, probably with respect to her entire body.