LIMBIC SYSTEM: PARTS AND FUNCTIONS (WITH PICTURES) - NEUROPSYCHOLOGY - 2025

The limbic system is a part of the brain made up of several anatomically and functionally interconnected structures that are involved in the processing of emotions. Many of these regions are located inside our brain, although there are some areas that belong to the cerebral cortex, such as the orbitofrontal cortex or the hippocampus.

The function 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, arousal level, and even some types of memory.

Source: Bruce Blaus CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)

The concept of "limbic system" is due to Paul MacLean, who in 1952 expanded the structures involved and defined the circuit in a more complex way. He also proposed the theory of the three brains, defending that the human brain was composed of different brains, the result 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 emotions. Finally, located on the outside, is the most recently acquired brain: the neocortex.

Parts of the limbic system and their functions

Interestingly, there is no universal agreement on the specific structures that make up the limbic system. The most commonly accepted are:

Limbic cortex

It is located around the corpus callosum, 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, one that integrates information of various types and brings it together 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?

- The cingulate gyrus: it involves part of the corpus callosum, it is in charge of processing and controlling the expression of emotions and learning them. It also seems to have an important role in motivation, being involved in goal-directed behaviors. It has been shown to be essential in maternal behavior, attachment, and reaction to smells as well.

- The parahippocampal gyrus: it is located in the lower area of ​​the cerebral hemispheres, below the hippocampus. It participates mainly in memory, more specifically, in the storage and retrieval of memories.

Hippocampus

Hippocampus and other brain regions

It is located in the middle part of the temporal lobe and communicates with the cerebral cortex, the hypothalamus, the septal area and the amygdala thanks to its multiple connections. Its most outstanding task is to consolidate learning and memory.

The hippocampus is responsible for introducing what we learn into our long-term memory store.

In fact, when there is an injury to this structure, you are not able to learn anything new, leaving your memories of the past intact. This is called anterograde amnesia. Why aren't older memories altered? Well, because they are stored in other places in the cerebral cortex, which, if not injured, the memories are still there.

The hippocampus is also active in the retrieval of memories. In this way, when we recognize something, such 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 should know that there is a very important link between emotions and memory. Specifically, an optimal level of emotional activation will facilitate the formation of memories.

Thus, we better remember those situations that had emotional significance for us, since we consider them more useful for our future than those that do not.

The hypothalamus

Hypothalamus

The hypothalamus is an important structure that is located in the lower part of the thalamus, inside the optic tracts. One of its most important functions is to control that the functioning of our body is kept in balance.

It has many connections to 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, hormonal levels, etc.

In short, it influences autonomic functions, the sympathetic nervous system (typical stress responses such as increased heartbeat and sweating), the 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

Brain tonsil (yellow)

The amygdala is one of the most studied structures of the nervous system and most directly linked to emotions. It is shaped like an almond and is made up of two nuclei, each located within a temporal lobe.

On the one hand, it seems that the stress hormones that are released when we have an important emotional experience, cause affective memories to be consolidated. And all that process is done by the amygdala.

In addition, this brain area is involved in the recognition of facial emotional expressions. It is a process that, although it may not seem like it, is carried out briefly, automatically, and even unconsciously. 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 in charge of 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, damage only to the amygdala leaving the hippocampus intact would make our subjects not learn to fear threatening stimuli, but they would learn the circumstances or environment where that event occurred.

While an exclusive lesion in the hippocampus would affect the learning of conscious contextual cues, but would not alter the learning of conditioned fear.

The septal area

It sits just above the anterior commissure and has numerous connections to the hippocampus, hypothalamus, and other areas.

It seems to be in charge of inhibiting the limbic system and the level of alertness when they have been over-activated by a false alarm. Thanks to 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 states of activation that would be counterproductive for us.

The septal nuclei, in addition, have an integrating function of emotional, motivational, alert, memory aspects, and pleasant sensations such as sexual arousal.

Ventral tegmental area

Ventral tegmental area (VTA)

It is located in the brain stem and presents dopaminergic (dopamine) pathways that are responsible for pleasant sensations. If an injury is suffered in this area, the subjects will have difficulties to feel pleasure and will try to seek it through addictive behaviors (drugs, food, gambling…).

In contrast, if medial parts of the tegmental area are stimulated, subjects report feeling alert but irritable.

Insular crust

Insula or insular cortex

It is located within the Silvio fissure 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 such as love, hate, fear, anger, joy, and sadness.

It can be said that it gives meaning to the changes in the body, making the person aware that they are hungry or want to use a certain drug again.

Orbitofrontal cortex

Orbitofrontal cortex

It has connections with areas of the limbic system such as the amygdala, thus taking charge of encoding data on social signals, and planning these interactions with others.

It seems to be involved in our ability to ascertain the intention of others by their gaze, gestures and language. However, its influence on emotional processing and on the assessment of rewards and punishments cannot be denied.

An injury to this area has been shown to cause disinhibition such as hypersexuality, foul talk, childish jokes, lack of impulse control with drugs, addictions; as well as problems empathizing with others.

Basal ganglia

Basal ganglia in orange

Composed of nucleus of accumbes, caudate nucleus, putamen, globe pallidus, black substance… Mainly they are involved in motor control.

Parts like the nucleus of accumbens are fundamental in addictive behaviors, since 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 the limbic circuits involved in social cognition (such as those involving the amygdala, cingulate gyrus, and orbitofrontal cortex) do not function properly in individuals with autism spectrum disorders.

- Kluver-Bucy syndrome

This involvement arises from a bilateral removal of the amygdala and part of the temporal cortex. It was observed that the subjects presented hyperorality (they explored everything with their mouth), hypersexuality, appeasement, loss of fear and indiscriminate eating.

- Limbic encephalitis

It consists of a paraneoplastic syndrome that mainly affects the hippocampus, amygdala, insula, cingulate gyrus and orbito-frontal 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 lack of control. For example, fronto-temporal dementia is associated with symptoms of disinhibition typical of lesions in the orbital-frontal area of ​​the brain.

- Anxiety disorders

In schizophrenia there is a reduction in the volume of limbic areas, the neurons of the hippocampus are not properly organized and it is smaller, and in the anterior cingulate cortex and the thalamus there are fewer GABAergic (inhibitory) cells.

- Limbic epilepsy

Also called Medial Temporal Lobe Epilepsy (MLT). In this type of epilepsy, lesions are generated in structures such as the hippocampal gyrus, the amygdala or the uncus. This affects anterograde memory, that is, the patient has difficulty learning new things. Furthermore, these people are more prone to anxiety and depression.

- ADHD

There are authors who think that some failure in the limbic system may be the cause of Attention Deficit Hyperactivity Disorder. 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 certain studies, there are variations in the volumes of the frontal lobes, basal ganglia, hippocampus and amygdala in these disorders. There appears to be less activation in some areas of the limbic system.

References

1. Rajmohan, V., & Mohandas, E. (2007). The limbic system. Indian Journal of Psychiatry, 49 (2), 132–139.
2. Swenson, R. (2006). Chapter 9 - Limbic System. Retrieved on October 4, 2016, from REVIEW OF CLINICAL AND FUNCTIONAL NEUROSCIENCE.
3. Ramos Loyo, J. (2006) Influence of emotions in cognitive processes. In E. Márquez Orta (Ed.), Attention and its alterations: from the brain to behavior (42-47). Mexico: Editorial Manual Moderno.
4. Hernández González, M. (2002). Chapter 22: Neurobiology of Emotion. In M. Hernández González (Ed.), Animal and human motivation (335-342). Mexico: Editorial Manual Moderno.
5. Silva, JR (2008). Chapter 17: Functional Neuroanatomy of Emotions. In Slachevsky, A., Manes, F., Labos, E., & Fuentes, P. Treaty of Neuropsychology and Clinical Neuropsychiatry.
6. Boeree, G. (nd). The Emotional Nervous System. Retrieved on October 4, 2016, from Shippensburg University.
7. Insular cortex. (sf). Retrieved on October 4, 2016, from Wikipedia.
8. Orbitofrontal cortex. (sf). Retrieved on October 4, 2016, from Wikipedia.