Neuroscience Blog

Article Author: Brett J. Weiss

Researchers show that electrically stimulating a brain region called the anterior precuneus (aPCu) causes dissociative sensations from the body of falling or floating, suggesting its key role in bodily self awareness.

Highlights

• Stimulating the left aPCu is associated with the negative, fear-inducing sensation of falling, while prodding the right aPCu triggers a more favorable feeling of floating in some epileptic patients with surgically-inserted electrodes.
• The study’s data suggest the aPCu serves as a hub linking multiple brain regions that comprise our sense of bodily self, which helps us to psychologically construct and navigate scenes from our surroundings.
• The aPCu and its physical self-associated brain network are separate from but in close communication with another network — the default mode network — linked to our narrative self based on autobiographical memories and envisioning future scenarios.

Consciousness has been a hot topic in the neuroscience field since around the 1980s. Along those lines, researchers continuously seek a more accurate understanding of the neural underpinnings for consciousness. Some scientists studying consciousness have focused on sensations originating from within humans based on autobiographical memories, the “me” in daily conversation. Other consciousness researchers prefer to focus on our physical sense of self and representations of our bodies in the brain — what we call the acting agent “I.” While the interconnection of brain regions forming a network tied to our autobiographical “narrative self” has largely been attributed to the “default mode network,” a brain network behind our physical sense of self has remained speculative.

Published in Neuron, Parvizi and colleagues from Stanford University School of Medicine show that the aPCu, sandwiched between the two brain hemispheres, acts as a node for our bodily sense of self, linking other brain structures in a network to psychologically construct and help us navigate our physical surroundings. Interestingly, electrically stimulating the aPCu causes the fear-eliciting sensation of falling or the positive sensation of floating, whether the stimulation occurs on the left or right side, respectively. Based on brain region connectivity analyses, Parvizi and colleagues found the physical self-associated brain network is distinct from but in close communication with the “narrative self” network — the default mode network. These findings can help researchers gain a more comprehensive view of constituent brain networks facilitating consciousness and provide insight into neurological disorders where people experience dissociating from their physical bodies.

“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 on the world around you. Nobody shares it,” said Parvizi in a press release. “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.”

The Anterior Precuneus Acts as a Brain Network Hub for Our Bodily Sense of Self, the “I”

Based on previous findings in one patient with seizures from excessive neuroexcitation localized near the aPCu who experienced being detached from his or herself and the reality of the outside world, Parvizi and colleagues sought to find how the aPCu relates to our brain’s representation of the bodily self. To do so, they measured how stimulating this region affects one’s subjective experience and how this relates to perceptions of themselves.

The researchers analyzed nine medication-resistant epilepsy patients who underwent procedures where electrodes were surgically implanted into their brains to monitor epileptic activity and localize the regions that seizures emanate from. In these patients, stimulating the aPCu was associated with a mixture of subjective states, depending on the stimulated location and the electrical intensity. Some subjective state generalizations across participants were evident, though. In five participants, stimulating the left side of the aPCu was associated with falling or being dropped, dizziness in three participants, and a lack of focus in two participants. In three of the participants, stimulating the right aPCu was associated with a floating sensation. Three of the nine participants also reported a sense of dissociating from themselves when the right aPCu was stimulated. Another participant reported a feeling of being thrown up in the clouds and out of his or her body. Two participants with right aPCu stimulation also reported that their experience reminded them of a self-dissociative experience they had while using psychedelics. Since stimulating the aPCu distorted participants’ sense of bodily location that was contrary to other sensory information, these data suggest the aPCu plays a crucial role in our sense of physical self.

“All of them reported something weird happening to their sense of physical self. In fact, three of them reported a clear sense of depersonalization, similar to taking psychedelics,” said Parvizi in a press release.

The Stanford researchers used brain blood flow (functional magnetic resonance imaging [fMRI]) data compiled from the nine study participants along with that from 900 participants in a publicly available database called the Human Connectome Project. They used this data to map the functional connectivity — when brain activity correlates between regions over time — to construct a brain region network tied to the aPCu. In doing so, they identified regions including the somatosensory area and the premotor cortex, regions involved in monitoring physical sensations and planning movement, respectively, linked to the aPCu. They also found that this network isn’t involved in self-referential and autobiographical memory and isn’t part of the default mode network. These results suggest that the aPCu acts as a node for the bodily sense of self and is distinct from the default mode network.

Finding How the Default Mode Network Interacts with Our Bodily Sense of Self

The study provides interesting data helping to define the neural network tied to our sense of bodily self. By shedding light on the key node for our bodily sense of self, the aPCu, Parvizi and colleagues have made it easier to identify certain types of epilepsy that involve losing one’s sense of orientation in relation to their surroundings. Other neurological disorders where patients feel like limbs are detached or have sensations of being dissociated from their bodies likely relate to this bodily self network as well. Future research uncovering more detail about this brain network will likely help with treatment options for these patients.

Since sensory information related to our bodily self, the “I,” is necessary for constructing an autobiographical self, the “me,” the two brain networks for both of these processes somehow closely interact and communicate. The next step for researchers could be to disentangle how these two networks interact with each other to generate our collective consciousness experience.

Story Source

Lyu D, Stieger JR, Xin C, Ma E, Lusk Z, Aparicio MK, Werbaneth K, Perry CM, Deisseroth K, Buch V, Parvizi J. Causal evidence for the processing of bodily self in the anterior precuneus. Neuron. 2023 Jun 6:S0896-6273(23)00386-0. doi: 10.1016/j.neuron.2023.05.013. Epub ahead of print. PMID: 37295420.