Katharina Buczek
Led by physician-scientist Josef Parvizi, researchers from Stanford Medicine recently uncovered the shocking role of a tiny structure known as the anterior precuneus (aPCu)– which plays a key role in forming “I,” or our physical sense of self.
The structure is located right in between the two constantly collaborating hemispheres of the brain, and the team found that this epicenter is critical for merging information about motion, location, sensations, and muscle and joint positions to create a mental map of our sense of physical self.
To better explain the significance of aPCu, Parvizi relied on the notions of “I” and “me.”
“For every action we take, even during dreams, there’s always an agent behind it: We call that agent ‘I.’ ‘Me’ is everything we have stored in our memories about the ‘I,'” he said.
In the brain, different structures control two distinct systems that are always talking to each other.
One system deals with our physical sense of self—the “I”—which is like how we feel in our own bodies. The other is about our narrative self—the “me.” This part is about our memories, our habits, our personalities, how we feel about others, and what’s coming up next in life.
Our narrative self has a well-known home in the brain. It’s called the default mode network. Even though it might sound like three random words thrown together, this term actually tells us about a network in the brain that gets busy when we’re daydreaming or remembering things.
The bodily-self network doesn’t have a catchy name yet, but scientists know it’s there. Previous studies have pointed out bits and pieces of it, but now there’s more info about its main player, the aPCu.
To get more details about this network led by the aPCu, Parvizi’s team did some brain imaging. They looked at data from five patients and nearly a thousand participants in the Human Connectome Project, which has been working since 2010 to map how the brain’s connections work.
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“We’ve shown the precise location of key cells in the aPCu, and Dian’s map clearly shows how they connect with the rest of the brain,” Parvizi said.
The aPCu is close to a part of the brain that’s a big deal in the default mode network. But it’s not actually part of that network, even though it chats with it a lot.
Stimulating the default mode network with electricity doesn’t change how you feel about yourself or how conscious you are, according to Parvizi.
“Your sense of physical or bodily self represents your organism in the immediate here and now, with a particular point of view that is yours alone, your first-person perspective of the world around you. Nobody shares it,” he explained.
“You may not be conscious of your point of view. But you will be if I disrupt the network that generates it. Your place in the world around you will suddenly seem unreal.”
Parvizi observes his patients who are being examined for potential surgical treatment for recurring seizures that drugs can’t control. The process involves fine needles, which function as electrodes, being inserted into the brain by a neurosurgeon while the patient is anesthetized.
The patients remain connected to monitoring equipment for several days. During this time, the electrodes track the electrical activity in the brain and send the data to a computer.
This method helps to capture the repeated seizures, and neurologists are then able to identify the exact location in the brain where these seizures are coming from. A significant number of patients have seen the end of recurring seizures due to this intrusive method.
With the approval of these patients, Parvizi sends small electrical pulses through individual electrodes. This alters or interrupts activity in very specific tiny areas of the brain, and he observes the effects. It’s essential to note that the procedure is safe, and the brain doesn’t feel any pain.
One patient shared with him, “Every time I have a seizure, I have a sense of depersonalization and dissociation. Everything’s unreal, not happening to me.”
It turned out that the aPCu was the origin of this patient’s seizures. Wanting to understand more, Parvizi and his team found eight more patients with electrodes in their aPCu, and these patients agreed to allow him to disrupt this part of the brain with electrical pulses.
