Summary: Researchers have identified a small structure in the brain, the anterior precuneus, or aPCu, as a crucial component in establishing our physical self, or “me.”
The APCu is part of a network of brain areas that integrate information about our location, movement and bodily sensations to form our self-awareness. When electrical activity in the aPCu is disrupted, people experience altered perceptions of their position in the world.
The findings expand our understanding of self-awareness and consciousness.
Key facts:
- The anterior precuneus (aPCu) in the brain plays a critical role in forming our physical sense of self, or “I,” as revealed by Stanford Medicine.
- When activity in the aPCu is disrupted, people’s perceptions of their place in the world change dramatically, producing a sense of depersonalization.
- The APCu works as part of a network of brain areas that integrate different types of bodily information to create our self-awareness.
source: Stanford
Have you ever wondered where that interesting character called “me” lives in your brain? Stanford Medicine physician-scientist Joseph Parvizi, MD, has news of his whereabouts.
If skulls were transparent, you still wouldn’t be able to see what was going on in someone else’s brain. But Parvizi has a way of getting inside people’s heads and finding out what makes us tick. His experiments have pinpointed specific areas of the brain that are critical for abilities ranging from perceiving faces to recognizing numbers.
Parvizi’s latest observation, described in an article published on June 8 in neuronreveals the surprising role of a small structure sandwiched between the two hemispheres of the brain.
The structure, called the anterior precuneus, or aPCu, is the epicenter of a system of distributed brain regions that hum in sync—their activity rising and falling in coordination with one another, indicating teamwork.
(Spoiler alert: Speaking of rise and fall, stay tuned for a description of people’s altered perceptions of their place in the world when their APCu goes haywire.)
Parvizi, postdoctoral fellow Dian Lu, Ph.D., and their colleagues found that this archipelago of cooperating brain regions, headed by the aPCu, is critical for integrating information about your location, movement, muscle and joint positions, and sensations, for to form a mental map of your sense of bodily or physical self.
To explain the meaning of the system, Parvizi refers to this strange pair of “I” and “me”.
“For every action we take, even in dreams,” he said, “there is always an agent behind it: We call that agent ‘I.’ “I” is all that we have stored in our memories of “I”.
The two selves
Neuroanatomically, there is a distinct archipelago of brain structures governing each. These two systems are constantly interacting with each other.
The physical/bodily sense of self – “I” – is contrasted with another, narrative aspect of self – “I” – which is associated with actively or passively thinking about your past life or planning your future: things like memory, habits, personality, emotions, feelings towards others, what is to come, etc.
The narrative self—”I”—lives in a well-studied network called the default mode network. (To the layman’s ear, the three words “default,” “mode,” and “network” read like a trio of random words singing imprecisely. But the term actually makes sense: it designates a brain network that’s active when you dream, recall past events and so on.)
There is no official name for the body web yet, although it is known to exist. Previous studies have highlighted the array of structures that make it up, but haven’t said much about its now-obvious king, the aPCu.
To further delineate the brain network driven by the aPCu, Parvizi’s team obtained brain imaging data from five of his participating patients as well as nearly 1,000 participants in the Human Connectome Project, launched in 2010 to map neural connections of the human brain.
“We showed the precise location of key cells in the aPCu, and Dian’s map clearly shows how they connect to the rest of the brain,” Parvizi said.
The aPCU is located near a brain structure that is considered a key node in the default mode network. But it is not part of this network, although it communicates intensively with it.
“Electrical network stimulation in default mode does nothing for self-esteem or consciousness,” Parvizi said.
“Your sense of physical or bodily self represents your organism in the immediate here and now, with a particular perspective that is yours alone, your first-person perspective on the world around you. No one shares it,” Parvizi said.
“You may not be clear about your point of view. But you will be if I cut the grid that generates it. Your place in the world around you will suddenly seem unreal.
A study of the brain
Parvizi made his observations on his patients who were being evaluated for possible surgical treatment of recurrent, drug-resistant epileptic seizures. Fine needles that serve as electrodes are inserted into the brain by a neurosurgeon under anesthesia.
Patients remain attached to the monitoring device for several days while the electrodes pick up electrical activity in the brain and report back to a computer.
The procedure ultimately captures the inevitable recurring seizures, allowing neuroscientists to pinpoint the exact location in each patient’s brain where the seizures originate. A significant number of patients are free from recurrent attacks as a result of this invasive approach.
With these patients’ consent, Parvizi passes small pulses of current through a series of individual electrodes, stimulating or interrupting activity in small discrete patches of brain matter and watching what happens. (The procedure is safe and the brain does not feel pain.)
One day a patient told him, “Every time I have a seizure, I have a feeling of depersonalization and dissociation. It’s all unreal, it’s not happening to me.”
The patient’s seizures appeared to originate from the aPCu. Wanting to learn more about what was going on, Parvizi and his colleagues found eight more patients with implanted electrodes going through their aPCu. The patients agreed to allow him to disrupt the activity of this structure with electrical impulses.
When he did this, Parvizi said, “They all reported that something strange was happening to their physical sensation. In fact, three of them reported a distinct sense of depersonalization similar to taking psychedelics.
But this sense of detachment was not an out-of-body experience.
“In an out-of-body experience, you see yourself from the top,” Parvizi said.
“Our subjects don’t report it at all. They still felt like they were in their bodies. But they usually report a change in their sense of their location and orientation.
“If the right side of the brain was stimulated, they felt like they were floating; if the left side was stimulated, they felt as if they were falling. As they looked around, it made no sense.
“They shouldn’t be floating or sinking, but I felt like they were. The world around them seemed unreal.
Curiously, patients’ reports of flying or floating versus falling or diving were accompanied by relatively positive versus negative emotions, respectively, depending on whether the right or left aPCu was electrically stimulated. (Like many brain structures, aPCu occurs in both hemispheres of the brain.)
“Why this is happening, I have no idea,” Parvizi said. “I’m absolutely baffled as to why stimulating the left side versus the right side produces opposite effects, but we’ll figure that out.”
About this news about the study of consciousness and self-awareness
Author: Bruce Goldman
source: Stanford
Contact: Bruce Goldman – Stanford
Image: Image credited to Neuroscience News
Original research: Free access.
“Causal evidence for bodily self processing in the anterior precuneus” by Joseph Parvizi et al. neuron
Summary
Causal evidence for bodily self processing in the anterior precuneus
Accents
- We investigated the anterior precuneus (aPCu) with fMRI, intracranial EEG, and electrical stimulation
- Stimulation of the aPCu causes distortions in the ground body pattern and self-dissociation
- Responsive aPCu sites were not part of, but were networked in default mode
- We present a brain map of structures that are causally related to aPCu
Summary
To investigate the causal importance of the human posteromedial cortex (PMC) in processing sense of self, we examined a rare group of nine patients with electrodes implanted bilaterally in the precuneus, posterior cingulate, and retrosplenial regions with a combination of neuroimaging, intracranial recordings, and direct cortical stimulations.
In all participants, stimulation of specific sites in the anterior precuneus (aPCu) caused dissociative changes in physical and spatial domains.
Using single-pulse electrical stimulations and neuroimaging, we present effective resting-state connectivity of the aPCu hotspot with the rest of the brain and show that they are located outside the boundaries of the default mode network (DMN), but are reciprocally connected to it.
We propose that the function of this PMC subregion is integral to a number of cognitive processes that require the physical reference point of the self given its location in a spatial environment.