He limbic system Is a part of the brain composed of several anatomically and functionally interconnected structures involved in the processing of emotions.
Many of these regions are immersed in the interior of our brain , Which are known as subcortical structures (below the cerebral cortex). Although there are some areas of the limbic system that belong to the cerebral cortex, such as the orbitofrontal cortex or hippocampus.
The mission of the limbic system is to control those aspects related to the preservation of oneself and the survival of the species. For example, emotional responses, motivation, level of activation, and even some Types of memory .
History of studies of the limbic system
The concept of limbic system has undergone remarkable changes over time.
Apparently, the term was born in 1664 with Thomas Willis , Which defined a group of structures surrounding the brain stem as"limbus brain"("limbus"means border or border).
In 1878, Paul Pierre Broca Introduced"The great limbic lobe". It referred to an area of the brain that occupies from the curved edge of the cingulate gyrus to the parahippocampal gyrus. Although this mainly related to the smell.
However, the first author who spoke about the role that this structure has on the emotional plane was James Papez . This neurologist was famous for proposing an anatomical model for emotions (Papez circuit) in 1937.
But the true concept of the"limbic system", which is the one we use today, is due to Paul MacLean Which in 1952 expanded the structures involved and defined the circuit more complex. He also proposed the interesting Theory of the Triune Brain, arguing that the human brain was composed of three brains, the fruit of our evolution as a species.
Thus, the first and most basic would be the reptilian brain; Then the limbic system or intermediate brain, which is the old mammalian brain that originates the emotions. Finally, located on the outside, is the most recently acquired brain: the neocortex.
He also indicated that the limbic system can not work without the help of the neocortex (or our"rational"part), with which it establishes numerous connections for emotional processing.
Components of the limbic system and their functions
Curiously, there is no universal agreement on the concrete structures that form the limbic system. The most commonly accepted are:
Limbic bark
Hard body
It is located around the hard body , And is a transition zone, since information is exchanged between the neocortex and subcortical structures of the limbic system.
It is an area of association, that is, that integrates information of various types and gathers it to give it meaning. Thus, we can give an interpretation to something that has happened to us and classify it as pleasant, unpleasant, painful, or pleasant.
What areas does it include?
- Cingulate gyration: wraps part of the corpus callosum, is responsible for processing and control the expression of emotions and learn them. It also seems to have an important role in motivation, being involved in goal-directed behaviors. It has been shown to be essential also in maternal behavior, attachment, and reaction to odors.
- The parahippocampal gyrus: is located in the lower area of the cerebral hemispheres, below the hippocampus. Participates mainly in memory, more specifically, in the storage and retrieval of memories.
Hippocampus
It is located in the middle part of the temporal lobe and communicates with the cerebral cortex, hypothalamus, septal area, amygdala ... thanks to its multiple connections. Its most outstanding task is to consolidate learning and memory.
The hippocampus is responsible for introducing into our long-term memory store what we learn.
In fact, when there is an injury in this structure you are not able to learn anything new, leaving your memories of the past intact. This is called Antegrade amnesia . Why do not the oldest memories alter? Because they are stored in other places in the cerebral cortex, which, if not injured, the memories are still there.
He hippocampus Also is active in the recovery of memories. In this way, when we recognize something, as a place or a path, we owe it, in part, to this structure. In fact, it is essential for our spatial orientation and for identifying clues from the environment that are known to us.
Why is this structure part of an emotional system? Well, you must know that there is a very important link between emotions and memory. In particular, an optimum level of emotional activation will facilitate the formation of memories.
Thus, we remember better those situations that had emotional meaning for us, since we consider them more useful for our future than those that do not.
The hypothalamus
Hypothalamus
He Hypothalamus An important structure that is located in the inferior part of the thalamus, inside the optical tracts. One of its most outstanding functions is to control that the functioning of our organism stays in balance.
It has many connections with very diverse areas of the brain: frontal lobes, brainstem, spinal cord , Hippocampus, amygdala, etc.
It has sensors that come from most of our body: olfactory system, retinas, viscera... In addition to being able to capture temperature, glucose and sodium levels, hormone levels, etc.
In short, it influences autonomic functions, in the sympathetic nervous system (typical stress responses such as increased heartbeat and sweating), parasympathetic (regulation of internal organs when we are at rest), endocrine functions, and behaviors such as reactions Emotional.
It is associated with appetite (lateral hypothalamic area) and satiety (ventromedial nucleus of the hypothalamus), sexual responses, and regulation of Circadian rhythms (Sleep and wakefulness).
The amygdala
The amygdala One of the structures of the nervous system More studied and more directly linked to emotions.
It is almond shaped and consists of two nuclei, each located inside a temporal lobe.
On the one hand, it seems Stress hormones Which are released when we have a significant emotional experience, strengthen affective memories. And the whole process is performed by the amygdala.
In addition, this brain area intervenes in the recognition of facial emotional expressions. It is a process that, although it does not seem like it, is realized in a brief, automatic, and even unconscious way. This is very important for proper social interaction.
Another essential function of the amygdala is to process fear in behavioral conditioning. That is, learning that a stimulus or environment is associated with some danger, so our body must prepare to defend itself.
Therefore, the amygdala would be responsible for learning and storing the implicit memories of fear (more unconscious); While the hippocampus would acquire declarative memories (those that can be consciously evoked).
For example, only damage to the amygdala leaving the hippocampus intact would cause us subjects not to learn to be afraid of threatening stimuli, but they would learn the circumstances or environment in which that event occurred.
While an exclusive lesion in the hippocampus would affect the learning of conscious contextual cues, it would not alter the learning of conditioned fear.
The septal area
It is situated just above the anterior commissure and has numerous connections with the hippocampus, hypothalamus and other areas.
It seems to be responsible for inhibiting the limbic system and alert level when they have been overactivated by a false alarm. Through this regulation, the individual will be able to maintain their attention and memory, and will be ready to respond correctly to the demands of the environment.
That is, it controls extreme trigger states that would be counterproductive to us.
Septal nuclei also have an integrative function of emotional, motivational, alert, memory, and pleasurable sensations such as sexual arousal.
More areas associated with the limbic system:
Tegmental Ventral Area
It is located in the brainstem and presents dopaminergic pathways (of Dopamine ) That are responsible for pleasant feelings. If an injury is suffered in this area, the subjects will have difficulty in feeling pleasure and will try to look for it through addictive behaviors (drugs, food, games of chance...).
In contrast, if medial parts of the tegmental area are stimulated, the subjects indicate that they feel alert but irritable.
Island crust
Insula
It is located within the fissure of Silvio and traditionally seems to have an important role in the processing and interpretation of pain, especially its anterior area.
In addition, it processes subjective aspects of primary emotions like love, hate, fear, anger, joy and sadness.
It can be said that it gives meaning to the changes of the organism, making the person aware that they are hungry or want to reuse some drug.
Orbitofrontal cortex
Orbitofrontal cortex
It has connections to areas of the limbic system such as the amygdala, which is responsible for coding data on social signals, and planning these interactions with others.
It seems that it participates in our capacity to ascertain the intention of the others by its look, gestures and language.
However, their influence on emotional processing and the valuation of rewards and punishments can not be denied.
It has been shown that an injury in this area causes disinhibition as Hypersexuality , Talk dirty, puerile jokes, lack of impulse control with the Drugs , Addictions; As well as problems to empathize with others.
Basal ganglia
Composed of nucleus of accumbes, caudate nucleus, putamen, pale globe, Black substance ... They are mainly involved in motor control.
Parts such as the nucleus of accumbens are fundamental in addictive behaviors, as here are the reward circuits of the brain and the sensations of pleasure. On the other hand, they also deal with aggression, anger and fear.
Conditions in which the limbic system is affected
- Autism
It appears that limbic circuits involved in social cognition (such as those involving the amygdala, cingulate gyrus and orbitofrontal cortex) do not function adequately in individuals with Autistic spectrum .
- Kluver-Bucy syndrome
This affectation Arises from a bilateral extraction of the amygdala and part of the temporal cortex. It was observed that the subjects presented hyperorality (they explored everything with the mouth), hypersexualidad, appeasement, loss of fear and indiscriminate feeding.
- Limbic encephalitis
It consists of a paraneoplastic syndrome that mainly affects the hippocampus, amygdala, insula, cingulate gyrus and orbitofrontal cortex. Patients develop memory loss, dementia, and involuntary movements.
- Dementia
Certain forms of dementia Can affect the limbic system or associated parts, producing symptoms of emotional uncontrol. For example, fronto-temporal dementia is associated with disinhibition symptoms characteristic of lesions in the orbitofrontal area of the brain.
- Anxiety disorders
It may be that in the anxiety disorders There is a failure in the control that cortical structures and the hippocampus must exert in the modulation of the amygdala.
- Schizophrenia
In the schizophrenia There is a reduction in the volume of limbic areas, hippocampal neurons are not properly organized and is smaller, and in the anterior cingulate cortex and thalamus there are fewer GABAergic (inhibitory) cells.
- Limbic epilepsy
Also called Temporal Lobe Medial Epilepsy (MLT). In this type of epilepsy , Lesions are generated in structures such as the hippocampus, amygdala or uncus. This affects the anterograde memory, that is, the patient has difficulty learning new things. In addition, these people are more likely to suffer from anxiety and depression.
- ADHD
There are authors who think that a failure in the limbic system may be the cause of Attention deficit disorder and hyperactivity . It appears that the hippocampus of these patients is larger, and also that there are no effective connections between the amygdala and the orbitofrontal cortex. Therefore, they can participate in the uninhibited behavior typical of these subjects (Rajmohany & Mohandas, 2007).
- Affective Disorders (Depression)
According to some studies, there are variations in the volumes of the frontal lobes, basal ganglia, hippocampus and amygdala in these disorders. Apparently there is less activation in some areas of the limbic system.
References
- Rajmohan, V., & Mohandas, E. (2007). The limbic system. Indian Journal of Psychiatry, 49 (2), 132-139.
- Swenson, R. (2006). Chapter 9 - Limbic System. Recovered on October 4, 2016, from REVIEW OF CLINICAL AND FUNCTIONAL NEUROSCIENCE.
- Ramos Loyo, J. (2006) Influence of the emotions in the cognitive processes. In E. Márquez Orta (Ed.), Attention and its alterations: from the brain to the behavior (42-47). Mexico: Editorial Moderno Manual.
- Hernández González, M. (2002). Chapter 22: Neurobiology of emotion. In M. Hernández González (Ed.), Animal and human motivation (335-342). Mexico: Editorial Moderno Manual.
- Silva, J.R. (2008). Chapter 17: Functional Neuroanatomy of Emotions. In Slachevsky, A., Manes, F., Labos, E., & Fuentes, P. Treatise on Neuropsychology and Clinical Neuropsychiatry.
- Boeree, G. (s.f.). The Emotional Nervous System. Retrieved on October 4, 2016, from Shippensburg University.
- Insular cortex. (S.f.). Retrieved on October 4, 2016, from Wikipedia.
- Orbitofrontal cortex. (S.f.). Retrieved on October 4, 2016, from Wikipedia.