The insular cortex, also called the insula, lobus insularis or insular lobe, is one of the most mysterious parts of the human brain and is barely larger than a 2 euro piece. Evolutionarily, this part of the human brain is ancient and performs many different tasks, not all of which have been discovered yet.
What is the insular cortex?
Even if you could look at the brain from the outside, you would hardly see the insular cortex. It lies hidden in the depth of the cerebral groove (sulcus lateralis cerebri) and is covered by the frontal lobe, parietal lobe and temporal lobe.
Anatomy and structure
As the cortex of the terminal brain, the insular cortex consists of gray matter with multiple layers of neuronal bodies. It is connected to the limbic system. To date, science has not been able to truly decipher what tasks the insular cortex has to perform. However, it is now clear that it is at least partly responsible for many feelings. It is involved in the ability to smell and to taste, and at the same time in the evaluation of what we have tasted and smelled. Whether something turns us on or off, pleases or disgusts us, the insular cortex most likely plays a very important role in this as well. But far beyond that, the insular cortex is also likely to receive and transmit signals from all internal organs. Are we nauseous or dizzy, are we hungry or thirsty, do we feel short of breath, is our bladder full, are we hot or cold? The insula is involved in all these (unconscious) feelings. But that is still not enough. Through its connection to the limbic system, the insula cortex is reciprocally connected to the thalamus and the amygdala, and thus it also has an influence on our consciousness and emotions. It is directly or indirectly (in what way is still unclear) involved in how we emotionally evaluate situations. Empathy, compassion, maternal love, even orgasm are, in a broader sense, co-controlled by the insula, as are disgust, revulsion, rejection. Some researchers therefore call this part of the brain the “island of the soul”. But the insular cortex has also been shown to be involved in language production.
Function and tasks
Brain research is a very complex and very difficult task. After all, it not only has the task of understanding how the brain functions as an organ, which is already very complicated. It also has to try to fathom how the link between brain activity and our thinking and feeling actually works. If we realize that in the brain an estimated 100 billion nerve cells communicate with each other via 100 trillion synapses, the extent of the difficulty in understanding or even influencing these processes becomes clear. Nevertheless, there are already promising approaches today. For example, brain researchers can measure which parts of our brain are particularly active under which conditions and to what extent they are used. Various imaging techniques are available for this purpose, such as magnetoencephalography. Here, sensors measure the electrical activities of the nerve cells. They are converted into images and so it is possible to see how strong the activity of certain brain areas is under certain circumstances. And it is precisely in this way that brain researchers have been able to find out a lot about the work of the insular cortex. For example, in studies using imaging techniques, neuroscientists have shown that the inula is active, not only in response to our own pain but also in response to observed pain. This is evidence that it is involved in compassion one of the most human abilities of all. It has also been shown through different patterns of activity that the anterior part of the insular cortex recognizes what feelings we have, while the posterior part can distinguish how strong the feeling is, where something hurts, for example, and what kind of pain it is. However, there is also research on how people behave in whom the insular cortex has been damaged by diseases and accidents. For example, patients with an injury to the inula have been found to have a partial but also complete disorder of sound attribution (audithoric agnosia). Other patients have, for example, lost the sense of smell or taste or the sense of hunger and thirst after a stroke in the area of the insular cortex. A patient who was previously a heavy smoker completely lost the pleasure of smoking due to damage to the insular cortex.
Diseases
If we now have a rudimentary understanding of what the insular cortex controls, this will provide clues as to what diseases changes in the insula may be associated with. A whole range of mental and physical health disorders come into question here. For example, autism, addictions, anxiety disorders, obsessive-compulsive disorders, and depression may well point to a disorder of the insular cortex. Much research has already been done on this topic. For example, scientists have studied autistic mice and found that they had a mismatch between inhibitory and excitatory impulses in the insular cortex. This disorder could even be partially corrected with medication. The mice showed less stereotypic behavior, their social behavior improved, and they interacted much more. Of course, there is still a very long way to go before this research can also lead to possibilities for treating diseases in humans, but the road is leading in that direction.
