The insula: anatomy and functions of this part of the brain.

We review the characteristics, anatomy and functions of this brain region.

By now it is known by the vast majority of the population that the human brain is divided into four cerebral lobes.

With a simple image of the encephalon we would be able to locate a large number of parts of the brain. However, there is a very relevant structure that may remain hidden from visual observation, considering that it is located at a certain depth behind one of the main sulci of the brain. This structure is called the insula.

What is the insula?

Also considered as the fifth cerebral lobe, the insula is a structure of the cerebral cortex located at the depth of the Sylvian fissure, at the point where the temporal, parietal and frontal lobes meet, being delimited by their respective opercula.

The insula is part of the mesocortex, or paralimbic system, together with the orbitofrontal and other structures. It is a connection center between the limbic system and the neocortex, participating in many different functions either directly or indirectly.

A part of the cerebral cortex

Understanding what the cerebral cortex consists of can help to understand the type of processes that take place in the insula.

The cortex of the brain, of which the insula is a part, is the rough part of the brain that extends through the brain. the rough part that extends over most of the outside of the brain.. However, as we have seen, it is not defined by being on the outside and fully exposed to observation, since the insula is hidden and the brain must be manipulated to see it. However, the reason why it is in the superficial part of the central nervous system is the same reason why the rest of the cortex is arranged in this way: the need to accumulate gray matter in strategic areas.

The gray matter is composed of neuronal somasThese are the parts of the neurons in which the nucleus is located and in which the most important processes of nerve transmission take place. These receive information from other parts of the nervous system, and at the same time send information to other parts of the nervous system.

But to centralize all these tasks requires space, and that is why the cerebral cortex exists: its rough, folded shape is designed to concentrate as much gray matter as possible in it, in an almost uninterrupted continuum along the outer (and not so outer, depending on how deep the folds and fissures are) surface of the brain.

Thus, both the insula and the rest of the lobes of the brain are not passage areas for nerve impulses, but regions in which complex psychological processes take place and in which information from very diverse areas of the nervous system is integrated.They are regions in which complex psychological processes take place and in which information from very diverse areas of the nervous system is integrated.

Components of the insula

The insula is not just a uniform structure that performs the same functions in a homogeneous way, but different parts of this structure are responsible for different parts of this structure are in charge of different tasks.. Specifically, the insula is divided into anterior and posterior insula, separated by the central insular sulcus.

The posterior region of the insula is mainly innervated with somatosensory neurons, which are the ones that create a "map" of the positional sensations related to the different parts of the body, so the participation of this region will be more related to the control of the viscera and internal organs.

The anterior part of this brain structure is more closely linked to the limbic system, being its functionality more oriented to the emotional integration of experiences and perceptions as a unitary and global sensation.

Main functions of the insula

Let us look at some of the main functions of the insular region.

As we have seen, the insula influences a large number of basic and higher processes (related to abstract thinking and decision making), and is an element of great importance for the correct functioning and even survival of the organism. In this sense, research carried out in the field of neurosciences reflects that the insula is involved in the following processes.

1. Taste perception and olfaction

The sense of taste has its main primary sensory area in the lower end of the insula and in the parietal cortex. and in the parietal cortex. It is at this point that taste information becomes conscious, appearing as a private and subjective experience but related to the elements of the environment that we taste.

It has also been observed that the insula participates in the perception of smell, although this sense tends to have a neural network dispersed throughout the encephalon.

2. Visceral control and somatoperception

The insula also plays an important role in the regulation of viscera and organs.. Specifically, it has been observed that its experimental manipulation produces important variations in Blood Pressure and heart rate. It also participates in the sensations coming from the digestive system, participating also in the management of this system and of the respiratory system.

3. Vestibular function

The vestibular function, which refers to body balance and control of the body in relation to space, also presents afferences to the insular region, being a relevant nucleus in its conscious perception. Thus, thanks to the insula, a healthy person is able to know what position each of the main parts of his body occupies at all times.

4. Integration of emotional and perceptual information

The insula, as mentioned above, acts as an area of association between many different parts of the body, acts as a zone of association between very different observationsThe insula, as mentioned above, acts as a zone of association between very different observations, especially with regard to the association between perception and emotion.

Thus, thanks in part to this brain region we learn from our experiences, since we link pleasant or unpleasant subjective sensations to what we do and say and, in this way, we associate behaviors to consequences through what we perceive.

5. Involvement in addictions: cravings and craving.

Due to its relationship and connections with the limbic system, the link between the insula and the brain reward system has been explored. Research has shown that this structure is involved in the processes of addiction to certain drugs, contributing to the maintenance of addictive behavior.

This relationship is due to the involvement of the insular region with the integration between emotion and cognition.being especially involved in the phenomenon of craving or intense craving.

6. Empathy and emotional recognition

Earlier we saw that the insula has strong connections with the limbic system. In this regard, recent research has indicated that this region of the cerebral cortex plays a key role in the capacity for emotion recognition and empathy. and empathy. Thus, it has been shown that those individuals without insula have a much lower recognition, especially with regard to the emotions of joy and surprise, as well as pain.

In fact, it has been suggested that the deficits found are very similar to some cases of autism, borderline personality disorder and behavioral problems, which could lead to research on the functioning of this brain area in certain disorders.

Bibliographical references:

• Allen, G.V.; Saper, C.B.; Hurley, K.M. & Cechetto, D.F. (1991). Localization of visceral and limbic connections in the insular cortex of the rat. J Comp Neurol; 311: 1-16.

• Craig, A.D.; Reiman, E.M.; Evans, A. & Bushnell, M.C. (1996). Functional imaging of an illusion of pain. Nature; 384: 258-260.

• Duque, J.E.; Hernán, O. & Devia, A. (2004). The insular lobe. A visceral cortical processing lobe. Acta Neurol. colom. Vol 20, 2.

• Guenot, M.; Isnard, J. & Sindou, M. (2004) Surgical anatomy of the insula. Adv Tech Stand Neurosurg; 29:265-288.

• Guyton, A. C. & Hall, J. E. (2008): Treatise on medical physiology (11th ed.). Madrid, Elsevier.

• Kandel, E. R.; Schwartz, J. H.; Jessell, T. M. (2001). Principles of Neuroscience. Madrird: MacGrawHill

• Kivity, S.; Ortega-Hernandez, O.D. & Shoenfeld, Y. (2009). Olfaction a window to the mind. Isr Med Assoc J; 11: 238-43.

• Kolb, B. & Wishaw, I. (2006). Human neuropsychology. Madrid: Editorial Médica Panamericana

• Manes, F. & Niro, M. (2014). Using the brain. Buenos Aires: Planeta.

• Netter, F. (1989). Nervous system. Anatomy and physiology. Volume 1.1. Barcelona: Salvat.

• Ostrowsky, K.; Isnard, J.; Ryvlin, P.; Guénot, M.; Fischer, C. & Mauguière, F. (2000). Functional Mapping of the insular cortex: clinical implication in temporal lobe epilepsy. Epilepsia; 41: 681-6

• Pedrosa-Sánchez, M.; Escosa-Bagé, M.; García-Navarrete, E. y Sola, R.G. (2003). Ínsula de Reil y epilepsia farmacorresistente. Rev. Neurol.; 36 (1): 40-44

• Snell, R.S. (1999). Neuroanatomía Clínica. Buenos Aires: Editorial Médica Panamericana, S.A:267.

• Türe, U.; Yasargil, D.C.H.; Al-Mefty, O. & Yasargil, M.G. (1999). Topographic anatomy of the insular region. J Neurosurg; 90: 720-33.

• Varnavas, G.G. & Grand, W. (1999). The insular cortex: morphological and vascular anatomic characteristics. Neurosurgery; 44: 127-38