By Olivia Guy-Evans, published April 22, 2021
by Saul Mcleod, PhD
The limbic system is a collection of structures involved in processing emotion and memory, including the hippocampus, the amygdala, and the hypothalamus. The limbic system is located within the cerebrum of the brain, immediately below the temporal lobes, and buried under the cerebral cortex (the cortex is the outermost part of the brain).
The limbic system was originally called the rhinencephalon (meaning ‘smell brain’) because it was thought to be primarily involved with the sense of smell.
Psychologists now recognize that the limbic system serves a lot more functions than previously believed. These structures are known to be involved in the processing and regulating of emotions, the formation and storage of memories, sexual arousal, and learning.
The limbic system is thought to be an important element in the body’s response to stress, being highly connected to the endocrine and autonomic nervous systems.
There are two widely accepted structures of the limbic system: the hippocampus and the amygdala. There are differing opinions as to which other structures are included in the system, and what only interacts closely with it.
The nerve cells (neurons) within the limbic system are structured differently to those in the cerebral cortex. In the cerebral cortex, the cells are mostly neocortical, meaning they are formed into six layers.
Within the limbic system, the cells are either arranged in fewer layers or are more jumbled. As there is less complexity of the cells within the limbic system, this had led people to believe that this system is evolutionarily older than the cerebral cortex itself.
There are two hippocampi, located in each hemisphere of the brain. They are seahorse-shaped and are structures mainly associated as being the memory centres of our brains.
Episodic memories are formed in the hippocampus and then filed away into long-term storage throughout other parts of the cerebral cortex.
The hippocampus always plays a role in spatial navigation and has also been associated with learning and emotions (Tyng, Amin, Saad, & Malik, 2017).
The hippocampus is also known as a site where neurogenesis occurs – this means that new nerve cells are made here from adult stem cells.
Due to the hippocampus’s involvement in memory, damage to this area can lead to severe memory impairments.
Damage can also be detrimental to spatial memory, for instance, remembering directions to locations that should be familiar to the individual.
The amygdala is an almond-shaped structure, located right next to the hippocampus. The main function of the amygdala is in emotional responses, including feelings of happiness, fear, anger, and anxiety.
This area is also key for the formation of new memories. The amygdala interacts with the hippocampus by attaching emotional content to memories.
It has a role in how memorable memories can be – memories that have strong emotional components tend to stick, rather than those with little emotional content. ‘Fear learning’ is also an element of the amygdala.
Fearful memories can be formed after only a few repetitions, which can result in avoidance of certain fearful stimuli. Therefore, the amygdala is also linked with the fight-or-flight response, as stimulating activity in the amygdala can influence the body’s automatic fear response.
Damage to the amygdala can result in more aggression, irritability, loss of control of emotions, and deficits in recognising emotions, especially recognising fear.
There are also links of amygdala differences in those with Autism, depression, posttraumatic stress disorder, and bipolar disorder.
The following structures are not structures of the limbic system, but form complex networks and interact closely with the limbic system, aiding in many functions.
The cingulate gyrus is part of the cingulate cortex of the brain and is thought to be an integral part of the limbic system.
This area is believed to be helpful in regulating emotions, behavior, and pain, as well as being responsible for controlling autonomic motor function.
This area is thought to be involved in fear and the prediction and avoidance of negative stimuli, through monitoring the body’s response to unpleasant experiences.
Damage to the cingulate gyrus can result in emotions being inappropriate, having a lack of fear, impaired sense of pain, and learning impairments.
This region has also shown differences in structure in those with Autism, depression, obsessive compulsive disorder, posttraumatic stress disorder, and bipolar disorder, due to its role in emotional processing (Yucel et al., 2003).
The hypothalamus’ most basic function is in homeostasis (maintaining a steady internal state).
This region controls most autonomic functions such as hunger, thirst, body temperature, blood pressure, heart rate, and sexual activity. The hypothalamus also serves as an interface between the nervous system and the endocrine system and in the regulation of sexual motivation and behavior.
The hypothalamus also has a role in controlling the body’s response to stress. In order to control these many functions, the hypothalamus integrates information from other parts of the brain and is responsive to a variety of stimuli, such as light, odor, stress, and arousal.
If the hypothalamus is impaired, this can lead to aggressive behavior, feeling over-stressed, hypothermia, hyperthermia, fatigue, weight gain/loss, and an active/under active sex drive.
Differences in the hypothalamus have also been associated with conditions such as depression, bipolar disorder, and schizophrenia.
The basal ganglia are a group of structures, situated at the base of the forebrain and top of the midbrain.
Its main functions are to regulate voluntary movements, including eye movements, help with balance as well as posture.
There is a limbic region of the basal ganglia which has multiple components (nucleus accumbens, ventral tegmental area, and ventral pallidum).
These areas have shown to be involved in cognitive and emotional behaviors, and with having a role in rewards and reinforcements. Because of this, it can be linked with addictive behaviors and the formation of habits.
Damage to the basal ganglia in general can result in tremors, involuntary muscle movements, abnormal posture, and links to movement disorders (Parkinson’s and Huntington’s disease).
In relation to the limbic system, the basal ganglia may also contribute to depression (Stathis et al., 2007).
Damage to the limbic system is dependant on which region is affected. Amygdala damage could affect a person’s fear processing (especially in being unable to recognize fearful situations), which could result in more risk-taking behaviors and putting themselves in dangerous situations.
Damage to the hippocampus could lead to deficits in being able to learn anything new, as well as affecting memory.
Hypothalamus damage can affect the production of certain hormones, including those which can affect mood and emotion.
Below is a non-exhaustive list of symptoms associated with limbic system damage:
- Uncontrolled emotions – more aggression, anxiety, and agitation.
- Olfactory impairments
- Memory impairments
- Abnormal sexual behavior – high/low sex drive
- Abnormal biological rhythms
Below are some cognitive disorders which have shown to be connected to the limbic system:
- Depression
- Olfactory impairments
- Obsessive compulsive disorder
- Anxiety
- Posttraumatic stress disorder
- Schizophrenia
- Bipolar disorder
- Autism spectrum conditions
- Alzheimer’s disease
- Movement disorders – Huntington’s and Parkinson’s disease
A potential treatment for limbic impairments is deep brain stimulation (DBS). Successful treatment of some cognitive disorders such as anxiety and posttraumatic stress disorder has come from DBS of the amygdala.
DBS has also shown to be useful in targeting the nucleus accumbens (part of the basal ganglia) in relation to drug addiction (Bari, Niu, Langevin, & Fried, 2014).
Similarly, the use of antidepressant medications has shown links with restoring the underlying physiological differences in the limbic system in major depressive disorder (Maletic et al., 2007).
This could be due to the personal involvement by participants when they make emotional judgments involving themselves. The participants may have seen deceit as a personal threat, therefore leading to increase amygdala activity as a result.
They found that the cingulate cortex, hippocampus, and amygdala had observable differences in structure. They also found that difference in white matter volumes tended to be more focal to the limbic system.
Compared to a control group, the former NFL players had reduced volumes of the amygdala, hippocampus, and cingulate gyrus. Therefore, this may be a potential indicator of neurodegeneration in those at risk of developing CTE.
Valdois et al., (2019) found that impaired attentional systems within the temporal lobes can be associated with developmental dyslexia.
There may also be a link between auditory cortex damage/deficits and schizophrenia, as damage in this area is linked to major symptoms of schizophrenia (e.g. hearing voice and auditory hallucinations).
Olivia Guy-Evans obtained her undergraduate degree in Educational Psychology at Edge Hill University in 2015. She then received her master’s degree in Psychology of Education from the University of Bristol in 2019. Olivia has been working as a support worker for adults with learning disabilities in Bristol for the last four years.
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