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The Human Limbic System: The Brain's Emotional Core

Aunice Reed has a M.A. in Marriage and Family Therapy from Touro University. She has a M.S. in Addiction Counseling and B.A. in Psychology.

The Great Limbic Lobe

Overview

Residing deep within the brain's center, lay a group of closely associated structures most noted for governance of emotion, sensation and motivation. These structures are collectively referred to as the “limbic system,” a label first coined in the 1950's by American doctor and neuroscientist Paul MacLean, who is also well-known for development of the Triune Brain Model. The limbic system, responsible for autonomic nervous system functioning, is necessary for control and regulation of vital survival mechanisms of hunger, thirst, heart rate, temperature and more. So it is with good reason that these structures are set deep inside the midbrain, as they are well protected in this region.

Paul Broca, a neurologist, first established the term “limbic” in 1878 when he began to refer to the parahippocampal and cingulate gyri as the “great limbic lobe.” He attributed the name limbic to describe the arching border area of the cortex, as it is comprised of both structures. At the time he did not elaborate on the purpose or functioning of these structures, but only noting their shape and presence. Broca also understood this distinctive area of the brain exists in all mammals.

The Limbic System is the Neural Basis of Emotion

The limbic system is what makes us human; it is how we feel and experience emotion. But what is emotion exactly? When we speak of emotion we are referring to happiness, sadness, anxiousness, contentment, and fear. The limbic system is also the neural basis of the human experience of love. But interestingly, there isn't an emotion system in the same way that sensory system functioning can be described and mapped. For example, we know that when we touch something hot (stimulus) the neural response occurs and it registers as pain. And there is a motor reaction to this. We move away from the harmful stimulus. Emotion is not mapped this way.

So while the limbic system is not the emotion system per se, it makes the processing and experiencing of human emotion possible. These interlinked structures: the amygdala, hypothalamus, cerebral cortex, thalamus and hippocampus all work together to bring about feelings.

The Human Brain is Actually 3 Brains-in-1

Human brain evolution suggests a 3-in-1 theory. This idea was developed by Paul MacLean, the person who discovered and named the Limbic System.

Human brain evolution suggests a 3-in-1 theory. This idea was developed by Paul MacLean, the person who discovered and named the Limbic System.

Triune Brain Theory

According to MacLean, the brain can be viewed through an evolutionary lens depicting three distinct phases: the paleomammalian complex, the reptilian complex and the neomammalian complex. The paleomammalian complex consists of the limbic system, while the reptilian complex encompasses the basal ganglia and is the oldest of the three. The youngest portion, the neomammalian complex, is the neocortex.

The reptilian complex (basal ganglia) is associated with vital functions: breathing, heart rate and body temperature regulation. It is termed the reptilian brain complex due to the presence of the brainstem and cerebellum, which encompasses the entire brain of all reptiles. MacLean also suggests that this area of the brain is necessary for instinctive behaviors such as territoriality and aggression. The basal ganglia is important for motor control and procedural learning. Parkinson's disease, a condition affecting more than 10 million people globally as of 2021, is caused by reduced neuronal output from the basal ganglia. This leads to the production of excessive movement in people diagnosed with Parkinson's Disease.

The neomammalian complex (neocortex) is thought to have appeared first in primates and later in humans. This section of the brain, MacLean purports, is responsible for making abstract thought, creativity, learning and language possible. It is the upper-most part of the human brain which is divided into left and right cerebral hemispheres.

The paleomammalian complex (limbic system) is where emotion is produced. It is necessary for memory formation and attribution of memories to human experiences. First appearing in mammals, the paleomammalian complex is essential for making judgments relating their importance and priority. The hypothalamus, hippocampus, and amygdala are the most important structures of the limbic system.

Human Brain Evolution and Triune Brain Model: Table

* = million years ago
The Triassic and Jurassic periods are both part of the Mezozoic Era. The R-Complex are the oldest brain structures of the human brain.

Brain NameLocationEpoch/EraFunctionAnimals

Neocortex

Towards the front of the head, and superior (on top of) limbic system

Eocene & Oligocene ~ 56 to 23 mya*

For processing thought, logic and reasoning

Primates. Particularly Homo sapien sapien (humans)

Limbic System, "paleomammalian complex"

center of the brain, on top of the R-Complex

Jurassic ~ 201 to 145 mya*

For mood, affect, memory and hormone regulation

dogs, cats, mice

Reptilian Brain (or R-Complex)

brain stem, cerebellum and basal ganglia.

Triassic ~ 252 to 201 mya*

For fight-flight-freeze response, temperature, heart rate and hunger/thirst

All reptiles, including dinosaurs.

Hypothalamus

Necessary for hormonal balance and excretion, the hypothalamus can be found next to the pituitary gland, connected by a stalk of nuclei and hangs beneath the brain encased in a cradle of bone. Survival of mammals requires that blood composition and body temperature fall within a specific range. The hypothalamus is responsible for regulating and maintaining these restrictive ranges in responding to environmental changes. This process is referred to as homeostasis.

Additionally, the hypothalamus is extremely important for regulating hunger, thirst, sex, blood pressure, mood, fluid-electrolyte balance and biological rhythm. Many pathways are contained in the hypothalamus, and are beneficial for communicating with the forebrain and other midbrain structures. Lesions and stimulation of the hypothalamus may cause violent rage and aggression, as well as changes in vital functions. The response may vary and is determined by the location of the hypothalamus damage or stimulation. For instance, stimulation to the lateral hypothalamus produces a silent biting attack in cats.

Hippocammpus

Particularly associated with long-term and spatial memory, the hippocampus is found in the middle of the temporal lobe. Essential for learning, the hippocampus communicates directly with the amygdala and the entorhinal cortex, both of which have pathways to and from other areas of the brain, such as the neocortex, the largest portion of the cerebral cortex. Damage to the hippocampus can lead to anterograde amnesia, a condition causing the individual to lose the ability to form new memories, so that anything that happens after the date of injury will be immediately forgotten. Events that occurred prior to injury are still retrievable.

Parts of the hippocampus, also referred to as the hippocampal formation.

Parts of the hippocampus, also referred to as the hippocampal formation.

The Amygdala

The amygdala consists of a pair of almond-shaped organs residing medially within the temporal lobe and in front of the hippocampus. The principle structure of the limbic system, the amygdala is associated with fear and aggression, and receives input from all sensory areas. Lesions and damage to this area causes a flattened emotional affect, characterized by a considerable decrease in emotional response particularly in situations where fear and aggression would be considered reasonable or logical. Research findings indicate that rats receiving an amygdalaectomy on both sides will fearlessly approach a cat. A lynx, normally a wild cat will exhibit the temperament of a domestic house cat. Amygdala damage produces an inability to recognize a familiar face in humans.

Amygdala Fast Facts:

  • The amydala plays a major role in fear and anxiety. People with bilateral damage show an atypical trust for strangers and cannot discern harmful situations.
  • The site of action for anti-anxiety medications is the amygdala.
  • The amygdala has receptor sites for opiates and benzodiazepines.
  • Stimulation of the amygdala produces fear and anxiety.
  • Certain foods and nutrients help to calm anxiety: chamomile tea, tryptophan (found in turkey), tumeric, advocado, Magnesium (found in leafy greens like Swiss chard and spinach), omega 3s (found in fish like Salmon, Mackerel, sardines, caviar and soybeans) and asparagus (Cole, 2019).

Reward Pathways are Located Within the Limbic System

As previously mentioned, limbic system structures such as the hippocampus and the cerebral cortex are necessary for the experience of learning and memory. These same structures are involved in the processing of reward, which is the reason that receiving a reward increases the likelihood of repeat behaviors. Habit formation occurs because reward triggers learning and this information is quickly stored in long-term memory. It is simple to recall a highly pleasurable experience, or even a painful one. Good habits like getting homework completed or changing poor eating habits can be positively reinforced with praise or a tangible reward of choice. Consequently, behaviors considered as "bad habits" such as overeating, gambling, excessive alcohol consumption and drug use are also reinforced in the same way.

How The Reward System Works: A Brief Tutorial From the National Institute on Drug Abuse (NIDA)

Common Diseases Involving the Limbic System

Epilepsy is characterized by involuntary movement and sensation disturbances, as well as altered levels of consciousness, caused by excessive, uncoordinated neuronal activity. Frequently described as a “brain storm,” epileptic seizures are classified as partial or generalized, depending upon whether the affected individual experiences unconsciousness or not. If the person has a loss of consciousness, it is typically called a grand mal, a generalized seizure. Most seizures are of the temporal lobe type, and are the predominate kind of seizure. It is thought to be caused by hippocampal sclerosis, a condition in which cells of the hippocampus atrophy and die.

Schizophrenia refers to a serious, chronic mental condition which causes an abnormal interpretation of reality. Symptoms include hallucinations, delusions, lack of emotional expression, uncoordinated movements and speech. The specific cause of schizophrenia is unknown, but several structural brain abnormalities have been discovered in patients with the condition. Strong genetic links have also been identified, such that certain gene types have been found to be affecting the action of the neurotransmitter dopamine, as well as epinephrine and norepinephrine. Research reports state that the hippocampus plays a role in the psychotic symptoms of schizophrenia.

Post-Traumatic Stress Disorder (PTSD) primarily involves the amygdala and hippocampus. It is manifest by flashbacks, panic attacks, constant remembering and re-experiencing details of a traumatic event. PTSD occurs due to actual exposure to a life-threatening situation, such as a natural disaster, sexual assault, war and witnessing suicide or homicide. When fear is experienced, the amygdala switches on the fear reaction (fight, flight or freeze) and a memory trace is created. Under normal conditions the hippocampus will shut down the "fear reaction" when the threat is over, but in the case of PTSD, it fails to do so. With PTSD, the fear response system is faulty and as a result, it is unable to properly regulate itself.

Alzheimer's Disease (AD) occurs as a result of plaques developing in the hippocampus (important for memory), causing neurodegenerative disease and neurocognitive problems. Plaques also grow in areas of the cerebral cortex, affecting judgement, reasoning and decision-making processes. No cause has been identified as of yet, but there are some increased risk factors for developing Alzheimer's Disease, such as insulin resistance, hypertension, being overweight, aging and having a familial history. Those with Down's Syndrome and Traumatic Brain Injury (TBI) are also at increased risk.

Science has advanced considerably since the old days of lobotomies, when it comes to comprehending how the brain is involved in regulating emotions. We now know that the concept of a lone system controlling all of human emotion is simplistic and unlikely. Emotion, with all of it's facets, especially as it relates to mood, actually requires action of and involves many areas of the brain. We also know that the particular type of stimulus experienced determines the areas stimulated.

Dr. Robert Sapolsky, Neuroscientist Limbic System Lecture - Stanford University School of Medicine

References

Cole, W. (2019, September, 5). 13 Foods to Help Ease Anxiety and Stress. Functional Food. Retrieved from: mindbodygreen.com

Lakhan, S.E. (2021, July, 20). Alzheimer disease. Medscape. Retrieved from: emedicine.medscape.com

National Institute on Drug Abuse. (2014, November, 18). The Reward Circuit: How the Brain Responds to Natural Rewards and Drugs. National Institutes of Health. Retrieved from: drugabuse.gov

Parkinson's Foundation. (2021). Understanding Parkinson's: Statistics. Retrieved from: parkinson.org

This content is for informational purposes only and does not substitute for formal and individualized diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed medical professional. Do not stop or alter your current course of treatment. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2015 Aunice Yvonne Reed

Comments

Aunice Yvonne Reed (author) from Southern California on April 09, 2015:

Thanks for stopping by DrBillyKid! I do agree though, yes it is absolutely true that fear is paralyzing. I have experienced this myself and its like the brain stops working for a couple of seconds and the response is delayed. Thanks so much for your encouragement.

Dr Billy Kidd from Sydney, Australia on April 08, 2015:

Great article! You did it grandly!

Neuropsychology should be required of every clinical psychology program. Knowing these things has helped me in many ways.

I would like to add one thing. I call it the 3-Fs: Flight-Fight-or-Freeze.

To nail this down, think of the deer in the headlights effect--the deer freezes at seeing the bright light.

Now think back at pre-mammalian development. Many insects freeze instead of moving when there is a perception of danger--because they instinctively don't want to be noticed due to their movement.

Now think of stage fight. A person often says they start off scared but once they start speaking they ease up and it goes OK. This goes way back to when mammals, including the homo species, froze when there was danger so they didn't move and get noticed by a predator. At those times, the vocal system froze too.

Now humans have evolved a little. But think about it. A woman facing rape often freezes and is physically unable to scream. So there is some of the remnants of the "freeze when in danger complex" still in the brain.

I don't mean to lecture, but it's something that no one seems to have brought forth into the popular media. And perhaps I've overly exaggerated it

Good luck with your writing! It's concise and clear. I really hope you continue you graduate work.

Aunice Yvonne Reed (author) from Southern California on April 08, 2015:

Glad you enjoyed the article, pstruabie48:). I work in the medical field, and I have to say that the brain is truly awesome. I fell in love with the brain when I took my first anatomy/physio course and had the opportunity of holding one in my hands.

Patricia Scott from North Central Florida on April 08, 2015:

Quite an article filled with much information, some I knew, most not in this much detail. The brain is such a complex center of activity and I am always amazed that as much is known about it as there is. To me it is the last (fully) unexplored anatomical portion of our bodies.

Each new discovery is one more step to truly understanding.

Thanks for sharing.

Voted up and shared

Angels are on the way to you this afternoon ps

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