Scientists have mapped the human brain’s insular cortex, or insula, in unprecedented detail, identifying distinct regions associated with pain, internal bodily sensations and higher-order cognitive processes. The findings, published in Nature, suggest that this relatively inaccessible part of the brain does more than register signals from the body: it may also influence how people perceive and interpret those sensations.
The research identifies three functionally distinct areas within the insula. The rear region is associated with sensations such as pain, heat, tingling and numbness in specific parts of the body. The middle region is linked to sensations originating in internal organs, including nausea, pressure and feelings of fullness in the chest. The front region, meanwhile, communicates with other brain areas involved in cognition and emotion, indicating a role in processing the significance of bodily experiences rather than simply detecting them.
“Contrary to previous thinking, the insula is ‘not just reading the body. It is partly influencing the story about how the body should be felt’,” said Josef Parvizi, a physician-scientist at Stanford University in California and a co-author of the study.
The findings offer a more detailed account of how bodily sensations are organised in the brain and how physical signals may interact with the mental processes through which people interpret them. They also provide researchers with a basis for investigating how this system might differ in people with neuropsychiatric conditions, including chronic pain syndrome.
Lucina Uddin, a cognitive neuroscientist at the University of California, Los Angeles, described the study as “quite a feat”. She said it was among the most comprehensive investigations of the insula and its role in producing bodily sensations.
The insula has long presented a challenge for neuroscientists because it lies deep within the brain, making direct examination difficult. Earlier research had suggested that it receives signals from different parts of the body, including information about pain and pressure, and processes them into sensations that reach conscious awareness. However, much of the research on the human insula has relied on brain imaging to observe its activity when people experience particular sensations, Parvizi said.
To investigate the region more directly, Parvizi and his colleagues needed to stimulate different parts of the insula electrically and record the sensations that followed. Implanting electrodes deep inside the brains of healthy volunteers would have been unethical, so the researchers worked with 87 people who already had electrodes implanted for medical reasons.
The experiments extended over more than a decade. During that period, the researchers delivered electrical currents through the implanted electrodes to different sites within the participants’ insulas, allowing them to compare the sensations produced by stimulation of different regions.
Stimulating the rear of the insula generated pain, heat and other sensations, including tingling and numbness, which participants located in specific parts of their bodies, such as their arms or legs. Electrical stimulation of the middle region produced a different set of experiences, including nausea, pressure and feelings of fullness in the chest. These responses indicated a distinction between the processing of sensations associated with particular body regions and those arising from internal organs.
The results from the front of the insula were less direct. Participants experienced relatively few bodily sensations when this region was stimulated. However, measurements of electrical signals produced by neurons revealed increased activity in the area while participants performed a task designed to assess salience detection — the ability to focus on some information rather than other competing signals.
This activity suggested that the front of the insula has a stronger association with cognitive processing than with the immediate generation of bodily sensations. The researchers also examined communication between different parts of the region and found that the front section sent more signals to other parts of the insula than it received. That pattern suggests it may influence activity in the middle and rear sections.
Further findings showed that the front of the insula communicates with other brain regions involved in cognition and emotion. Together, these observations support the possibility that the insula participates in a two-way relationship between bodily signals and the brain’s interpretation of them. Physical sensations are processed within the insula, but activity in its front region may also influence how those sensations are experienced and understood.
Charalampos Labrakakis, a neuroscientist at the University of Ioannina in Greece, said the study’s scale and scope made it an important contribution to understanding the insula. Examining pain and other sensations across different parts of the body could help researchers establish how the region changes the way people experience them, he added.
The researchers’ next step is to investigate whether the insula’s organisation differs in people with neuropsychiatric disorders, including chronic pain syndrome. Parvizi said the objective was to apply the findings to conditions that can severely affect people’s lives. “We need to use this knowledge to understand disabling conditions,” he said.
