Scientists have reported on the role of different brain regions in the perception of illness

Feeling unwell may be associated with changes in the activity of many areas of the brain, including areas of the cortex involved in the perception of body condition. This conclusion was reached by scientists from the European Laboratory of Molecular Biology (EMBL), who studied the reaction of mice to a substance that transmits signals of inflammation. How the brain participates in the formation of weakness, fever and loss of appetite — in the material of Izvestia.

How the brain reacts to disease

Weakness, chills, fever, and lack of appetite often accompany infection. These manifestations add up to a general state of malaise, which changes habitual behavior: a person moves less, loses interest in food and tends to rest.

Scientists consider this reaction as an evolutionarily ancient defense mechanism that helps the body recover. At the same time, the brain plays a central role in coordinating the changes taking place.

Previously, researchers have already established that deep brain structures, including the hypothalamus and brain stem, are involved in the regulation of symptoms. However, it remained less clear what role the neocortex plays, a part of the cerebral cortex associated with information processing, planning, and controlling arbitrary behavior.

The authors of the new work focused on this issue. They suggested that malaise can be considered as a special brain condition in which the work of several interconnected areas changes.

According to her, the formation of such a condition probably requires the participation of vast areas of the brain or several of its areas.

How scientists caused malaise in mice

For the experiment, the researchers used prostaglandin E2, or PGE2. This signaling substance is produced in the body during inflammation and is involved in triggering reactions characteristic of the disease.

The scientists injected PGE2 directly into the brains of mice. This approach made it possible to quickly cause symptoms and observe changes in nervous activity over a short period of time.

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The symptoms of malaise appeared almost immediately. The animals' temperatures rose, they became less mobile and ate less. The symptoms persisted for about 30-45 minutes. Compared to traditional laboratory models, in which the development of a reaction can take hours or days, this significantly reduced the observation time.

The researchers analyzed the behavior of mice, mapped brain activity, and recorded the activity of individual neurons. The combination of methods made it possible to compare the external signs of malaise with changes in the nervous system. Senior author Robert Prevedel noted that the new approach helped to get a detailed picture of what was happening in a much shorter time.

Which area of the brain attracted the attention of researchers

After the introduction of PGE2, scientists discovered changes in activity in many parts of the network that monitors the internal state of the body. Thus, the reaction went beyond the individual structures traditionally associated with temperature regulation and other physiological functions.

The islet bark attracted special attention. In it, the researchers identified groups of nerve cells whose activity changed during experimentally induced malaise. The authors attribute this result to a possible important role of the insular cortex in the brain's response to disease.

Among other things, the iDISCO method was used to map activity, which makes it possible to visualize the distribution of markers of neuron activity throughout the brain. It was combined with the recording of the electrical activity of nerve cells.

The results obtained support the idea that the state of malaise is accompanied by distributed changes in brain function. At the same time, the involvement of many areas does not mean that all its departments react in the same way or perform the same function.

What do the results mean for understanding the disease?

According to Kamm, studying malaise as a separate brain condition can help understand why behavior and habitual decisions change during infection. Immune signals trigger a nervous system response that affects activity, appetite, and other manifestations of the disease.

However, the experiment was conducted on mice that were injected with a separate signaling substance. This model allows us to study certain mechanisms, but does not reproduce all the processes that occur during a natural infection.

In addition, the scientists assessed the temperature, behavior, and activity of the neurons. It is impossible to directly measure the subjective feeling of illness in animals. Therefore, the results help to study the biological basis of malaise, and transferring these findings to humans requires further research.