The limbic system is one of our brain's earliest regions, according to evolution. According to theories such as the triune brain model, it is also commonly called the emotional brain or emotional nervous system.
Research in the field of neuroscience has provided insight into the roles of the limbic system in behavioral and emotional responses and how it shapes our behaviors. The limbic system can also be called the limbic lobe.
Definition of the Limbic System
Limbic system is a region of the brain that acts as a networking system. With many interconnected parts, it is responsible for controlling a variety of emotional impulses, as well as being instrumental in memory formation.
The limbic system is made up primarily of the hippocampus, amygdala, thalamus, and hypothalamus. It is situated below the cerebral cortex.
Limbic System Functions
As mentioned, the limbic system functions as a signaling system to form and contribute to complex emotions and other brain functions such as memory. Despite the limbic system's many components, the point is that they generally work together. For example, although fear is most commonly associated with the amygdala, other brain areas also respond to fear.
Puberty is a crucial stage in the development of the limbic system, as significant changes occur. For example, the amygdala develops more and, combined with hormonal changes, can give rise to intense emotions such as anger, fear and aggression. Furthermore, throughout adolescence, the limbic system comes under greater control from the prefrontal cortex. This area does not fully develop until age 25 and is essential for reasoning, problem solving, and impulse control. The development of the prefrontal cortex is a biological reason why there is a perception that teenagers are moody due to these underdeveloped limbic structures.
Primary structure of the Limbic System
Hippocampus
The limbic system includes the Hippocampus, which comes from the Greek word for seahorse. It is located very deep in the brain and is associated with learning and specific aspects of memory such as spatial memory and spatial navigation.
In terms of memory, memory encoding: the process of allowing information to be encoded, stored and retrieved, is one of its main functions. Memory encoding, for example, might allow us to remember where we had lunch yesterday. Memory consolidation is another aspect of memory that the hippocampus is responsible for, allowing us to form more stable and lasting memories.
Amygdala
The limbic system also includes the amygdala, which is shaped like an almond and is responsible for emotional responses such as pleasure, anxiety, anger, and fear. The amygdala plays a role in memory and is close to the hippocampus in the brain. Specifically, it involves how firmly memories are stored, as memories are often associated with strong emotional ties that tend to stick around for much longer.
The connection between memories and fear is through the amygdala, which can help form new fear-related memories. Learning through fear facilitates the aforementioned concepts such as memory consolidation.
It's an area of the brain that can generate quite intense emotions. Informally, the responses triggered by the amygdala are called "fight or flight," which, combined with the nervous system, is a natural physiological reaction to threats to survival from an evolutionary perspective. There are three distinct stages to the stress caused by these reactions: alarm, resistance, and exhaustion. In particular, much of the research is on the basolateral amygdala.
Thalamus and Hypothalamus
The thalamus is a component of the limbic system and is regarded as the relay station for sensations travelling throughout the body, with the exception of smell (smell) processing. It controls variations in emotional reactivity along with the hypothalamus. Any external event that sets off strong emotions is referred to as emotional reactivity.
One example involves the hypothalamus, which controls vital impulses for the body, such as sleep. In the absence of adequate sleep, other areas of the hypothalamus react. These areas are linked to emotions such as anger, displeasure, and disgust. So there is a clear link between key homeostatic processes such as sleep and emotional communication and the disruption of these processes.
Secondary or accessory brain regions
For brain regions to be regarded as key components, the limbic system's secondary or accessory structures must be present.
The cingulate gyrus is a structure that is close to the nose. This closeness helps associate smells and images with pleasant or adverse memories of past emotions. Also important is the function of the emotional response to pain. Aspects of pain, such as avoiding fear and unpleasant sensations, are processed in this area. Finally, aggressive behavior and impulsivity are also associated, although this is up for debate.
The basal ganglia are a secondary area of the limbic system as they are close to other limbic structures. It is well known for its significance in motor planning and execution. However, recent evidence suggests their roles in reward and reinforcement, addictive behaviors and habit formation. Psychiatric disorders such as depression and schizophrenia may involve a disruption in connections between the basal ganglia and the limbic system. As a result, implications for neuromodulation therapies have been suggested.
Finally, the cingulate gyrus is a structure that, along with processing emotions and regulating behavior, helps regulate autonomic motor function. Its location in the brain is fundamental, as it connects with the frontal, temporal and occipital cortex of the two hemispheres of the brain. Specifically, it coordinates sensory input with emotions. An example would be pricking your finger and then feeling pain. It also deals with the emotional responses associated with pain and regulates aggressive behavior.
Many other areas could be included as additional limbic structures, which suggests the complexity of this area. These include the septum, nucleus accumbens, orbitofrontal cortex, cerebral cortex, olfactory cortex, and many others. There are also subcortical structures to consider.
The Limbic System and Emotional Responses
At its basic level, affective processing is an activity within the brain that represents decision-making skills. Disruptions to affective cognition are often at the forefront of mood disorders. Many actions and decisions take place in an emotional context. So there is a link between cognitive functions and emotional states. Part of this process is labeling emotions as being positively or negatively valued. For example, emotions like happiness would have a positive valence, and disgust would have a negative valence.
A group of researchers analyzed affective processing abnormalities in criminal psychopaths using magnetic resonance imaging (MRI). They found that affective processing deficits occurred more frequently in response to stimuli with negative valence and that they required more cognitive resources to process and evaluate affective stimuli than the others. Regarding the brain, they found abnormalities in the anterior and posterior cingulum, inferior frontal gyrus, amygdala/hippocampus formation, and ventral striatum. In particular, the abnormalities were related to a lack of affect-related activity in these areas. So there were disturbances in the limbic system.
The Limbic System and Memory
The "greater limbic system" involves memory function. Specifically, memory is in the sense of organizing behaviors to ensure they are adaptive for survival.
Affective processing includes memory, affect, and goal-directed behaviour, as was indicated in the preceding section. Long-term memory is a type of memory that can be stored in the brain for years; there are two main groups of long-term memories.
The first is explicit/declarative memories for episodic instances that may occur throughout life. The second type falls into the group of implicit/procedural memories that are important for learning and remembering motor and cognitive skills. Depending on the group, different areas of the limbic system are involved. First, the hippocampus works with another area of the brain called the medial temporal lobe. The second is the basal ganglia, which also work with another vital region of the brain, the cerebellum.
The amygdala does not work alone in memory formation, consolidation, and retrieval of emotional memory functions. The limbic system functions as a neural circuit, whether in declarative memory formation, memory consolidation, contextual fear memory formation, trait conditioning, or conditional discrimination learning.
The Limbic System and Chronic Stress
Chronic stress can have detrimental impacts on physical and mental health. Chronic stress can be the result of many factors and permanently change the state of the body and mind. Numerous studies on the limbic system have focused on life trauma as a type of persistent stress. One study examined the hypothalamus, specifically the hypothalamic-pituitary-adrenal (HPA) axis. This is a complex set of direct influences and feedback interactions between three structures: the hypothalamus, the pituitary gland, and the adrenal glands on top of the kidneys.
This is a neuroendocrine system, which means that the hormones each of these structures release affect the nervous system as they travel through the blood. Each one releases a hormone that leads to the next one and it's a cascading effect. There is an effect on functions including digestion, the storage and use of energy, and mood in general.
That study found that lifetime trauma significantly affected the HPA axis and that lifetime trauma can make certain limbic regions more sensitive. Specifically, the limbic regions that contain the hippocampus and amygdala. This finding is consistent with research that has found that the amygdala plays a role in influencing the HPA axis for a stress response, triggering the release of stress hormones. This can result in problems with stress regulation and HPA axis function and lead to a risk of poor health outcomes. An example would be impaired memory consolidation. This is a clear example that limbic system dysregulation has a big impact.
Problems Related to the Limbic System
As it develops a series of activities in the human body, the malfunction of the limbic system can lead to various dysfunctions and diseases such as:
• Anxiety
• Memory problems (recent or long-term)
• Alzheimer's
• Schizophrenia
• ADHD (Attention Deficit Hyperactivity Disorder)
• Psychomotor Epilepsy
Conclusion
With numerous interrelated components, the limbic system is a complicated network. It has four main components and many additional structures that can be considered secondary - the subcortical structures and the cerebral cortex. Historically, the limbic system was presented as a system within the brain related to emotional states. However, it has recently been explored in relation to its implications for learning and the formation of new memories.
In addition, limbic system disorders and the impacts of chronic stress, as well as strategies to relax the limbic system, were discussed. The aim was to present the limbic system from a broad point of view and recognize how it contributes to well-being as a component of physical and mental health. Finally, stress management techniques are key to keeping this system in check.
