Relationship between prefrontal and limbic cortex: a comparative anatomical review.
The limbic system is a complex set of structures that lies on both sides of the . The prefrontal cortex, which is the part of the frontal lobe which lies in front of the motor The autonomic nervous system is composed of two parts, which function . Certain cortical areas of the frontal lobe which are included in the limbic system on functional grounds and by virtue of their hypothalamic and amygdaloid. It has a neurobiological basis and is associated with functional and structural 19 The hippocampus is the most widely studied brain structure in relation to.
Like the hippocampus, processes in the amygdala seem to impact memory; however, it is not spatial memory as in the hippocampus but the semantic division of episodic-autobiographical memory EAM networks. Markowitsch's  amygdala research shows it encodes, stores, and retrieves EAM memories. To delve deeper into these types of processes by the amygdala, Markowitsch  and his team provided extensive evidence through investigations that the "amygdala's main function is to charge cues so that mnemonic events of a specific emotional significance can be successfully searched within the appropriate neural nets and re-activated.
Attentional and emotional processes[ edit ] Besides memory, the amygdala also seems to be an important brain region involved in attentional and emotional processes.
The Limbic System
First, to define attention in cognitive terms, attention is the ability to focus on some stimuli while ignoring others. Thus, the amygdala seems to be an important structure in this ability.
Foremost, however, this structure was historically thought to be linked to fear, allowing the individual to take action in response to that fear. However, as time has gone by, researchers such as Pessoa,  generalized this concept with help from evidence of EEG recordings, and concluded that the amygdala helps an organism to define a stimulus and therefore respond accordingly.
However, when the amygdala was initially thought to be linked to fear, this gave way for research in the amygdala for emotional processes. Kheirbek  demonstrated research that the amygdala is involved in emotional processes, in particular the ventral hippocampus.
He described the ventral hippocampus as having a role in neurogenesis and the creation of adult-born granule cells GC. These cells not only were a crucial part of neurogenesis and the strengthening of spatial memory and learning in the hippocampus but also appear to be an essential component to the function of the amygdala.
A deficit of these cells, as Pessoa predicted in his studies, would result in low emotional functioning, leading to high retention rate of mental diseases, such as anxiety disorders.
Social processing[ edit ] Social processing, specifically the evaluation of faces in social processing, is an area of cognition specific to the amygdala.
In a study done by Todorov,  fMRI tasks were performed with participants to evaluate whether the amygdala was involved in the general evaluation of faces. After the study, Todorov concluded from his fMRI results that the amygdala did indeed play a key role in the general evaluation of faces.
However, in a study performed by researchers Koscik  and his team, the trait of trustworthiness was particularly examined in the evaluation of faces. Koscik and his team demonstrated that the amygdala was involved in evaluating the trustworthiness of an individual. They investigated how brain damage to the amygdala played a role in trustworthiness, and found that individuals that suffered damage tended to confuse trust and betrayal, and thus placed trust in those having done them wrong.
Furthermore, Rule,  along with his colleagues, expanded on the idea of the amygdala in its critique of trustworthiness in others by performing a study in in which he examined the amygdala's role in evaluating general first impressions and relating them to real-world outcomes. Their study involved first impressions of CEOs. Rule demonstrated that while the amygdala did play a role in the evaluation of trustworthiness, as observed by Koscik in his own research two years later inthe amygdala also played a generalized role in the overall evaluation of first impression of faces.
Evolution[ edit ] Paul D. MacLeanas part of his triune brain theory, hypothesized that the limbic system is older than other parts of the forebrain, and that it developed to manage circuitry attributed to the fight or flight first identified by Hans Selye  in his report of the General Adaptation Syndrome in It may be considered a part of survival adaptation in reptiles as well as mammals including humans.
These components are, respectively: The archipallium or primitive "reptilian" brain, comprising the structures of the brain stem — medulla, pons, cerebellum, mesencephalon, the oldest basal nuclei — the globus pallidus and the olfactory bulbs.
The paleopallium or intermediate "old mammalian" brain, comprising the structures of the limbic system. The neopallium, also known as the superior or rational "new mammalian" brain, comprises almost the whole of the hemispheres made up of a more recent type of cortex, called neocortex and some subcortical neuronal groups.
It corresponds to the brain of the superior mammals, thus including the primates and, as a consequence, the human species. Similar development of the neocortex in mammalian species unrelated to humans and primates has also occurred, for example in cetaceans and elephants ; thus the designation of "superior mammals" is not an evolutionary one, as it has occurred independently in different species.
The evolution of higher degrees of intelligence is an example of convergent evolutionand is also seen in non-mammals such as birds. According to Maclean, each of the components, although connected with the others, retained "their peculiar types of intelligence, subjectivity, sense of time and space, memory, mobility and other less specific functions".
However, while the categorization into structures is reasonable, the recent studies of the limbic system of tetrapodsboth living and extinct, have challenged several aspects of this hypothesis, notably the accuracy of the terms "reptilian" and "old mammalian". The common ancestors of reptiles and mammals had a well-developed limbic system in which the basic subdivisions and connections of the amygdalar nuclei were established.
While the anatomic structures of the limbic system are different in birds and mammals, there are functional equivalents. Society and culture[ edit ] Etymology and history[ edit ] The term limbic comes from the Latin limbusfor "border" or "edge", or, particularly in medical terminology, a border of an anatomical component. Paul Broca coined the term based on its physical location in the brain, sandwiched between two functionally different components.
The limbic system is a term that was introduced in by the American physician and neuroscientist, Paul D. Kluver and Bucy, after much research, demonstrated that the bilateral removal of the temporal lobes in monkeys created an extreme behavioral syndrome. After performing a temporal lobectomy, the monkeys showed a decrease in aggression. The animals revealed a reduced threshold to visual stimuli, and were thus unable to recognize objects that were once familiar.
He became interested in the brain's control of emotion and behavior. After initial studies of brain activity in epileptic patients, he turned to cats, monkeys, and other models, using electrodes to stimulate different parts of the brain in conscious animals recording their responses.
He analyzed the brain's center of emotions, the limbic system, and described an area that includes structures called the hippocampus and amygdala. Developing observations made by Papez, he determined that the limbic system had evolved in early mammals to control fight-or-flight responses and react to both emotionally pleasurable and painful sensations. The concept is now broadly accepted in neuroscience. MacLean enlarged his theory to address the human brain's overall structure and divided its evolution into three parts, an idea that he termed the triune brain.
In addition to identifying the limbic system, he pointed to a more primitive brain called the R-complex, related to reptiles, which controls basic functions like muscle movement and breathing. The third part, the neocortex, controls speech and reasoning and is the most recent evolutionary arrival.
Academic dispute[ edit ] There is controversy over the use of the term limbic system, with scientists such as LeDoux arguing that the term be considered obsolete and abandoned.
So let's get to a little more complicated diagram. And what you see here is my best attempt at drawing the limbic system.
Now, limbic system structures sit on top of the brain stem. And this is the brain stem. And you can imagine this as the very bottom of your brain. And here's the spinal cord coming out of it. And the spinal cord goes all the way down your back to about your tailbone. Now, the limbic system are these structures up here, that are drawn in bright colors. Now to orient you to this diagram, this is what you would see if you pulled off like the top part of your brain, which is called the cortex.
And it's facing in this direction. In other words, while this isn't anatomically correct, let's say your eyes are here, your nose is here, and your mouth is here. Again, this is not anatomically correct.
But this you can see is the front, and this is the back. So I kind of drew it at an angle so you kind of get a 3D idea. So let's remove this and go back to talking about the anatomical structures. So this blue thing here, this is called a thalamus. And you actually have two of these, one here and one on the other side. So your thalamus functions as like a sensory relay station, meaning the things that you see, hear, taste, touch, all these senses you have come through your nerves and ultimately end up in your thalamus.
And the thalamus directs these senses into the appropriate areas in the cortex, as well as other areas of the brain. And I mentioned this in terms of an emotion lecture because emotions are very contingent on the things that you see, the things that you touch and hear.
And you may have noticed there's one sense that I didn't mention. And that's a sense of smell. And the sense of smell actually is the only sense that you have that actually bypasses this thalamus. And instead, it has its own private relay station that, when it comes from the nose, it goes to a certain area in the brain. And that area of the brain actually happens to be very close to other areas that regulate emotion, which explains why sometimes certain scents can evoke very powerful memories and bring you back to a certain moment in time.
But in terms of emotion, I mentioned thalamus because of how the senses play an important role in your emotions. Now, you see here there's these two purple structures. And this is known as an amygdala.
Now, the amygdala is sometimes called the aggression center. And experiments have actually shown that if you stimulate the amygdala, you can produce feelings of anger and violence, as well as fear and anxiety. I'm going to put "stimulate" and represent it as dark green plus sign. So you stimulate the amygdala. It evokes feelings of anger, violence, fear, and anxiety. On the other hand, if you've destroyed your amygdala-- and I'll represent destruction as a negative sign-- if you destroy the amygdala, it can cause a very mellowing effect.
Kluver and a neurosurgeon by the name of Dr. And I mention Kluver and Bucy because in medicine there's actually a syndrome known as Kluver-Bucy syndrome. And that's when there's a bilateral destruction of your amygdala.
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And "bilateral" means both. And if you have bilateral destruction of the amygdalas, that can result in certain symptoms that are often seen, like hyperorality, which means you put things in their mouth a lot; also hypersexuality; as well as disinhibited behavior. And disinhibited behavior is when you ignore social conventions. You can act very impulsively. You don't consider the risks of your behavior. So you do dangerous, reckless things. So that's Kluver-Bucy syndrome. And that's again when you destroy both sides of your amygdalas.
And the way I remember this is I think if you stimulate the amygdalas, that can cause fear and anxiety. And people who have anxiety disorders or experiencing an anxiety attack sometimes are given a medication known as a benzodiazepine. Sometimes they're called "benzos.
And think of what happens when people consume too much alcohol. Sometimes you see these types of behaviors. You might be eating a lot. You might have hypersexuality.