What the anterior precuneus does for our sense of self : Short Wave : NPR
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What the anterior precuneus does for our sense of self : Short Wave : NPR

May 31, 2023

EMILY KWONG, BYLINE: You're listening to SHORT WAVE...


KWONG: ...From NPR.


Hey there, SHORT WAVErs. Aaron Scott here. And I'm curious, have you ever had an out-of-body experience? Because I'm having a little bit of one myself right now, being back here in the host chair. Like, it just doesn't seem real.

JON HAMILTON, BYLINE: Well, I hate to say it, Aaron, but I'm not sure scientists would consider that a real out-of-body experience, I mean, unless you're feeling like you're actually floating above your body or seeing yourself and the world from a location outside of your body.

SCOTT: OK, Jon Hamilton, I know you're NPR's brain expert, but that doesn't mean you have to go sciencing on my parade.

HAMILTON: Dude, I science on everybody's parade. It's my job.

SCOTT: (Laughter). Wait a minute, though. Are you actually saying that there are scientists researching out-of-body experiences?

HAMILTON: Well, yeah. There really are. I mean, scientists have known for a long time that, you know, different things can cause that perception - you know, near-death psychological trauma, certain mental health disorders. And, of course, you can have these experiences from drugs like ketamine or psilocybin. What has been a mystery, though, is what's really going on in your brain when you feel separated from your body. And now it looks like scientists are beginning to figure that out. They've even found a way to cause an out-of-body experience by stimulating one particular area deep in the brain.

SCOTT: That is very cool. And how did they find that area?

HAMILTON: It all began a few years ago with a man who was having these really unusual epileptic seizures. He happened to go see a neurology professor at Stanford named Dr. Josef Parvizi.

JOSEF PARVIZI: He came to my clinic and said, my sense of self is changing. I feel like I am a third observer to conversations that are happening in my mind. And plus, I'm having problem with my balance. I just feel like I'm floating in space.

SCOTT: Today on the show, exploring the brain circuits that anchor us to our bodies until they don't.

HAMILTON: And why it may be helpful to occasionally venture outside of your bodily self.

SCOTT: You're listening to SHORT WAVE from NPR.


SCOTT: So, Jon, this bodily self that you mentioned - what is it exactly?

HAMILTON: Well, it's a part of consciousness or self-consciousness. The idea here is that consciousness includes several different what you would call selves.


HAMILTON: So for example, we have what's known as our narrative self. It's the story of our life that we all carry around in our heads. You know, it kind of shapes our identity. Then there's a social self, which is how we see ourselves in relation to other people, but the bodily self or the physical self - it's much more basic.

SCOTT: And so that is the self that the seizure patient from earlier was feeling disconnected from.

HAMILTON: Right. He talked about feeling like he was floating separate from his body and being an observer to his own thoughts. Here's how Josef described what our sense of a physical self does for us.

PARVIZI: As you are sitting in your chair, you're looking at me. You have an understanding that it is you looking at me, your point of view in space and in your environment.

HAMILTON: Which is why we usually talk about ourselves in the first person.

SCOTT: Right, right, right. But this sounds more like philosophy, like the, I think; therefore I am. How does a brain scientist study this sort of thing?

HAMILTON: Well, they - in this case, they came to it kind of by accident.


HAMILTON: So Josef was actually studying something a little different, and that is the brain circuits involved in retrieving personal memories. Those are part of what you would call our narrative self, not our physical self.

SCOTT: OK. So memories are with the narrative self because they help make up our personal story of our life.

HAMILTON: Right. And in the middle of that work, Josef encountered the man with the weird epilepsy symptoms.

SCOTT: And you said he was having an out-of-body experience each time he had a seizure.

HAMILTON: Exactly. So Josef thought if he could locate the source of those seizures, it might tell him something about the brain circuits that usually tell us our body is our own. Finding the source would also, of course, help him treat the man's epilepsy. So a surgeon placed electrodes in different areas of the man's brain, and these wires let doctors see the electrical activity of brain cells, including the sort of activity that starts an epileptic seizure. In this case, the electrodes showed that the seizures were coming from an area called the postural (ph) medial cortex, or PMC. It's a fairly large area toward the back of the brain, and it's kind of nested between the two hemispheres. So to make sure they'd found the right area, they used those same wires in the man's brain to deliver these tiny pulses of electricity that kind of shut down that area. And, bingo, he began having these out-of-body experiences.


HAMILTON: But Josef says the team realized you had to stimulate one specific part of the PMC to get that result.

PARVIZI: What we discovered is that, towards the front, there is this thick gyrus, almost like a tiny kind of a thin sausage-looking piece of brain that is called the anterior precuneus.

HAMILTON: Right. It's your vocabulary word for the day, anterior precuneus.

SCOTT: Thank you.

HAMILTON: And what it is - it seems to be some kind of hub for information related to the self. At least it is when it's working correctly. But it turns out, all it takes is a little pulse of electricity to disrupt that hub. And then the information doesn't get through anymore. So it looked like that was all it would take to alter this patient's sense of self. And they had the results from one patient. But to test the idea, Josef said his team stimulated the anterior precuneus of eight more patients.

PARVIZI: And lo and behold, everybody has changes in their sense of not the narrative, not the mental self but what we call the physical self.

SCOTT: Josef actually sounds like this came as a surprise. Did he expect some sort of different result out of this?

HAMILTON: Well, sort of. He expected the patient's sense of self would change with the stimulation, but he was surprised that you could actually tweak the brain in a way that would affect the physical self but not the narrative self. And in this case, that was not affected. See - up to this point, Josef had thought both of these different selves were part of the same brain network. It's called the default mode network, and it's active even when you're not focused on anything in particular. Your mind is just wandering. The narrative self does appear to be part of that network, but the physical self seems to be part of a different network. And that was a surprise because Josef had thought our different selves would all be sort of tied together.

SCOTT: Jon, this is all surprisingly weighty stuff. I mean, for a lot of people, I feel like out-of-body experiences are proof that we have souls or spirits that exist separate from our bodies. But what you're saying is this kind of grand mystery of human existence is really just the result of a little bit of electrical stimulation?

HAMILTON: I think what scientists would say is that if you can create an experience through either a drug or a stimulation to a certain part of the brain, maybe you don't need a supernatural explanation, a metaphysical explanation.

SCOTT: OK. So spiritual and religious implications aside, tell me about the practical implications of this research.

HAMILTON: Well, one of them has to do with treating depression. Josef says a little brain stimulation might help by allowing a person to take an outside perspective of their own life.

PARVIZI: There are many conditions, neuropsychiatric conditions, where we have too much subjectivity and too much self-referentiality. Rumination is a notorious, notorious element of depressive conditions where everything becomes self-related. We take everything personally, and everything is self-referential.

SCOTT: That sounds like one of the big things that a lot of therapists work on.

HAMILTON: I mean, it is. And trying to take a more objective look at yourself is a part of cognitive behavioral therapy. And it may be one reason that dissociative drugs like ketamine and psilocybin - these drugs seem to work against depression, maybe because they help someone get outside themselves a little bit. It's also worth noting that studies in both animals and people have now shown that ketamine affects the anterior precuneus in pretty much the same way that brain stimulation does.

SCOTT: So a little brain stimulation could be just like taking ketamine.

HAMILTON: I mean, perhaps. I talked about that with a scientist at Harvard named Patrick Purdon. He was part of a team that found ketamine affects the anterior precuneus, and he told me there's a lot of interest in using brain stimulation instead of drugs for purposes like anesthesia and perhaps even for treating some psychiatric disorders.

PATRICK PURDON: Brain stimulation might be a more precise way of doing things in the sense that you could get the specific brain areas that you want without having to cause a brainwide and systemwide effect that might carry with it a lot of side effects.

HAMILTON: Now, nobody is putting wires in people's brains to anesthetize them for, like, surgery yet, but there are some studies underway of using brain stimulation, both from inside the brain with wires and outside the brain through transcranial magnetic stimulation, to deal with chronic pain. So it may be a route that is going to pan out.


SCOTT: Jon, thank you, as always, for helping us to step outside of ourselves for just a few minutes.

HAMILTON: Anytime, Aaron. Stay in your own body.

SCOTT: This episode was produced by Berly McCoy. It was edited by managing producer Rebecca Ramirez. Jon checked the facts. And Patrick Murray was the audio engineer. Beth Donovan is our senior director. Anya Grundmann is our senior vice president of programming. I'm Aaron Scott. Thanks, as always, for listening to SHORT WAVE from NPR.


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