How the brain creates a physical sense of our personality
Miscellaneous / / August 19, 2023
Scientists are investigating this issue to help people with depression and other unpleasant disorders.
In the 19th century, the American philosopher and psychologist William James put forward the theory that personality can be divided into two parts. The first - "I", or "pure ego" - physically perceives and feels the world around. The second - the "personality" proper, or "experiential ego" - includes a person's mental story about himself, based on past experience. Modern neuroscientists, armed with high-precision tools, set out to find the areas of the brain that are responsible for creating the two aspects of personality described by James. And we have achieved some success in this.
What areas of the brain are responsible for the mental and physical "I"
First, scientists discovered the empirical self. A key player in the mental part turned out network of the passive mode of the brain. By this term, introduced neuroscientist Markus Reichl in 2001, called areas of the brain that are active when a person is not solving any problems. Researchers also
figured outthat the passive mode network plays an important role in processing our thoughts about ourselves. So it can be called a kind of center of self-awareness.Finding the physical part of the personality was much more difficult, at least until recently. The awareness that we have a body creates a bridge that constantly switches between the conscious and unconscious states of the mind. Imagine that you are sitting at a table or standing at a bus stop. If you don't feel pain, you don't feel your left arm, right shin, or big toes every second. But as soon as you think about any of these parts of the body, you will feel it. The physical self is the feeling that you are actually inside your own body.
Looking for this "I" in the brain, scientists have come to the conclusion that the passive mode network will serve as a logical starting point. They were especially interested in one of its segments, known as the posteromedial cortex and located near the back of the head in the area where the two hemispheres meet.
Neuroimaging studies have shown that the posteromedial cortex is activated when we remember the past or when our mind wanders, causing us to think about ourselves. Therefore, the experts wanted to test whether the disruption of brain activity in this area could somehow change our physical sense of self. It didn't work. When scientists used electric current to stimulate the brains of epilepsy patients to influence their activity, the physical sense of "I" hasn't changed.
In 2018, the head of this study, neuroscientist Joseph Parvizi met an epileptic patient who has unusual symptoms. According to the patient, during seizures he fell into into a strange state of dissociation that left him uncoordinated and feeling disconnected from his inner self. When Parvizi and colleagues examined the patient's brain to find the source of the seizures, they were found to originate in an area of the posteromedial cortex called the anterior precuneus.
This unexpected discovery led to a new study. Scientists scored 8 patients whose epileptic seizures were not caused by the posteromedial cortex, but by other areas of the brain. Then they made sure that all the participants had healthy tissue in the area of the brain that was to be studied. Finally, electrodes were implanted into the posteromedial cortex for each of them for electrical stimulation.
Electrocution of the anterior precuneus resulted in all participants reporting changes in their subjective experience similar to those described by the patient Parvizi with unusual symptoms. They felt like they were floating, dizzy, lacking concentration, and detached from themselves. Some participants noted that this detachment resembled the state that occurs under the influence of psychedelics. Thus, scientists came to the conclusion that by stimulating the anterior precuneus, it is possible to cause distortions in our physical sense of self.
Why scientists study the mechanisms of physical self-perception
The results of the experiment by Parvizi and his colleagues help to better understand how the brain processes the sensation of our bodily self. And they coincide with the results of the work of a group of scientists led by cognitive neuroscientist Henrik Ersson. He and his team conducted independent research and figured outthat the anterior precuneus is activated when the physical sense of self changes under the effect of the out-of-body illusion. She made the participants in the experiment feel as if their real body was no longer part of themselves. To induce this state, they were shown a video of touching a stranger's body and simultaneously touched the participants in the same places.
Parvizi and his team relied on participant reports in their research, and Ersson said it would be useful to explore how stimulation of the anterior precuneus alters the physical self, through more objective methods such as behavioral experiments.
To understand how the anterior precuneus is connected to the brain's dormant mode network, Parvizi and colleagues placed five study participants in a functional magnetic resonance imaging scanner and recorded their brain activity in the state rest. The results showed that the areas of the anterior precuneus, on which changes in physical self-awareness depended, were not part of the network, although they formed connections with some of its areas.
This means that there are two different systems for processing the "I": the memory-based narrative "I" and the body "I". In other words, the two parts of James's personality reside in separate networks in our brains. One of the main questions that scientists want to answer in future studies is exactly how these systems interact with each other.
Parvizi hopes this work will help clarify what happens in conditions like depression, which are characterized by depressive rumination and intrusive negative thoughts about the self. According to the scientist, people suffering from such symptoms can get stuck in the pattern of perceiving the world around them from their point of view and lose the ability to look at what is happening from a third person. He wonders if people with depression can benefit from understanding how the interplay of narrative and body selves colors our memories based on subjective experience. And is it possible to break this terrible vicious circle of information about whether the cross-links between these two systems become hyperactive in people with depression.
Psychiatrist and neuroscientist Sahib Khalsa believes research can help explain elements of the out-of-body experience that people experience under the influence of psychedelics and non-drug drugs. For example, in a sensory deprivation chamber, when a person is weightless in a dark container filled with liquid, isolated from any sensations.
Khalsa along with colleagues also found changes in the anterior precuneus and other related brain regions in people who have received therapy in such a chamber. In addition, the study identified a potential region of the brain that could be targeted to treat patients with dissociative conditions. For example, if a person suffers from a functional neurological disorder, when problems at work nervous system can lead to a wide range of symptoms and diseases, and other disorders associated with injuries.
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