The Brain Structure as the Intermediary for the Emotions
-The Cerebral Limbic System -
The most important part of the brain which arouses emotions is included
in what is called the cerebral limbic system. This system is known as the
"animal brain". This is because it is considered to be the structure
and functions which all animals have in common. The limbic system is situated
in the upper brain stem and the lower cerebral cortex. All such structures
are connected by nervous pathway.
There are several structures which are linked reciprocally in the limbic system. The nucleus having the thalamus front part is included in the limbic system. Then, below this there is the small, but powerful hypothallamus. The nerve cells which particularly influence the actions of the independent nervous system of the heart beat and respiration etc., are concentrated in the hypothallamus.Then, it is this region which arouses most of the physiological changes accompanying the strong emotions.
In the deep part outside the brain, is the amygdaloid nucleus in the form of a cluster of walnut-size grey cells. Experiments in animals showed that there is a hippocampus at the side of the amygdaloid nucleus. Although the relationship between the occurrence of emotions and the hippocampus is still not clearly understood, because of the strong linking with the amygdaloid nucleus, it is thought to play some part. Many scientists consider that various forms of sensory information integration is carried out. If the hippocampus is damaged it will hamper the memory and new information will be unable to be sensed.
Surrounding the hippocampus and other linking system structures is the cingulate gyrus. Also, the bi-polar tropism fibre system forming the fornix runs parallel to the cingulate gyrus, connecting the hippocampus to the hypothallamus . The septum (separate structure) receives inputs from the hippocampus due to the cerebral fornix, and transmits neural outputs to the hypothallamus. Why any of the emotional colours are assumed in all the relationships with the environment relating to the flow of the brain neural routes, is understandable. The neural information inputs from all sensations pass through various levels of processing in the brain stem and cortex etc., or pass through both of these, the amygdaloid nucleus, the hippocampus and the limbic system. The information emitted from the cortex also passes through here.
In the brain stem the formatio reticularis plays an important part forming the level structure inside the pons cerebri and the brain stem (medulla oblongata). This receives sense information from various neural routes, operating as a type of filter, to keep if new information, only passing through continuous information. These fibres pass through the thallamus and some are projected into the cerebral cortex.
Most of the formatio reticularis nerve cells are considered "not unique". That is, for example, the formatio reticularis nerve cells can react to various information sources with the reaction to one type of sensory stimulus being different between the sense of sight, sense of hearing and action. Cells such as these send information from organs and structures such as eyes, skin and internal organs, to the cerebral limbic system and cerebral cortex etc.,
One of the functions within the formatio reticularis is called "city of the structure level". The caeruleun nucleus secretes norepinephrine neural transmission matter, and is a cell cluster of nerve cells in the independent source emission circuit. The route from the caeruleun nucleus is one which is conveyed up to the place holding the thallamus or hypothallamus, also widely projecting into the cerebral cortex. Other routes are conveyed down to the cerebellum or spinal cord. The neural transmission norepinephrine matter which is the product of special nerve cells such as these (secreted as hormones from the adrenal gland - adrenaline) arouses emotional excitement.
If the norepinephrine in the brain is too low a state of depression ensues, and if working for long periods too much norepinephrine, it is thought that an extreme stress reaction is aroused. The norepinephrine may also play an important part, when an individual experiences a pleasant feeling. Substance nigra, which is a separate "city-like structure in the reticular formation" located in the centre of the formatio reticularis which secretes the neural transmission matter dopamine, of course is a collection of independent emission system nerve cells. Dopamine is above all promoted by pleasant feelings. Then, it is also known that feelings of exhilaration generated by cocaine and amphetamines etc., are also related. Patients with Parkinsons disease have damaged substance nigra nerve cells and a deficiency of dopamine.
Patients like these who are prescribed L-DOPA are assisted in producing dopamine, but on the other hand, this will bring about symptoms similar to schizophrenia. From this fact, it is considered that an excess of dopamine is connected with schizophrenia itself.
Assuming the deepest relationship with emotions, in the cerebral cortex, in the frontal lobe, here receives a direct nerve projection from the thallamus. Because emotions and thoughts are not separate processes, although it is thought that the temporal lobes are also related to emotions, how such things as thoughts and emotions interact with one another is not fully understood.
It has been known since at least 1848 that the frontal lobe plays a part in the disposition and personality. In that year there was an explosion accident, in which the cranium of the 25 year old head railway track layer called Phineas Gage was pierced by an iron bar one metre long, weighing 60 kg. His left frontal lobe was cleanly removed as if by surgery. Miraculously, although his life was saved, his personality was changed completely. Prior to the accident, Gage was reliable, industrious and was liked by everyone. When he had recovered from the injury, he became unstable, noisy, unbelieving and impulsive.
His doctor described him as follows "he paid scant respect to his colleagues, when not satisfying their requests, was admonished, restrained, but became impatient, and occasionally very stubborn, however, on the other hand, he capriciously and consistently held on to unrealisable future plans" (Harlow, 1868 ).
It is not possible to reconstruct an accurate clinical picture of this case. Some of Gage's personality changes might have been an emotional reaction to the serious facial injury he sustained. For a while, he traveled all over with P T Barnham, taking the metal bar which had caused the accident, to show people. However, scientific research since has shown that the frontal lobe plays an important part, being linked with the thallamus, in emotional experiences and reactions.
Many anatomical facts are known about the neural routes which make contact between the brain and neural system parts and such limbic systems as the brain stem, cortex structures etc. However, concerning the emotions, in particular how such human emotions function, we are almost carried into the realms of supposition.
Experimental scientists have traditionally used two fundamental methods in spite of the research into the function of the cortex in contributing to the limbic system and emotions etc., These are (1) electrode stimulation of specific sites in the brain and (2) surgical destruction or removal of various sites within the brain. In stimulation experiments, researchers observed behaviour during stimulation, while in destruction research, the behaviour before and after surgery and comparison was made with the same kind of normal animal behaviour etc.,
In the early 1950's W. R. Hess conducted some pioneering research based upon implanted electrodes. When specific areas of the thallamus lower region of a cat were stimulated, an attack was observed which was typical when threatened. That is, the cat became angry, snarling and tail wagging furiously, claws out and hair standing on end. When a dog barked at the subject cat the behaviour shown by any cat was expressed. Moreover, without the external stimulation of a dog etc., only the nervous action aroused by the hypothallamus, namely the anger-based attack expression occurred.
In 1953, James Olds implanted an electrode in a different site than that in the experiment by Mr. Hess, in the hypothallamus of the cat. Animals were not only studied as to "pushing the lever" as a means of receiving a stimulus, but also the "lever pushing" was studied (when it was applied) once, 1,000 times per hour and then continuously for 10 hours. Having tried as hard as possible to obtain an electrical stimulus in mice it was considered that the feeling in mice based upon electrical stimulation is one of "liking". Because of this, this site in the hypothallamus is called "the pleasure centre". According to later research into "the pleasure centre" of animals, several parts of the brain have been identified as producing self stimulation in animals. This "reward route" passes through almost the same routes as those of the dopamine transmission nerve cells from the substantia nigra, and the norepinephrine transmission nerve cells from the locus coeruleus. Stimulation by electrodes, because the composition and emission of these two neural transmission substances is increased, due to the sensation of "reward" created by the electrode, if one or both of these nerve cells is activated, then it is supposed that this is a natural phenomenon("the reward pathway: in order to be effective, the stimulation must be delivered along "mesolimbic reward system". Dopamin is the neurotransmitter common to all of these structure; nucreus accumbens, the septum, and the ventral tegmental area etc.By the stimuli, such as food and sex , the reward pathway begin when neuron in the hypothalamus release serotonin.This triggers relearse of other neurotransmitters that in turn allow cell in the ventral tegmental area to release dopamine. Dopamin travels to the amygdala, the nucleus accumbens, and certain parts of the hippocampus. In the research of addiction, a clear signature for desire on the PET scan:the anterior part of the cingulated gyrus, the amygdala, and the nucleus accumbens-these are key stations in the mesolimbic plesure-reward system. Plevious animal studies that showed a gush of chemical messengers-dopamine principally-occurring in these site after cocaaine administration(this part was cited from The Secret Life of The Brain by Richard Restak.2001)
However, it cannot be concluded that such circuits actually 'bring about' rewards. Many patients who have been undergoing brain surgery, have also been tested with electrode stimulation. In fact many patients do not feel any pain when tampering with the brain organisation, but depending upon the patient it is necessary to be 'kept awake' during surgery. Many such patients are reported to have experienced a pleasant feeling associated with the "pleasure centre" identified in mice, through electric stimulation of sites in the brain.
However, the fact that electrical stimulation influences the emotional behaviour has been shown most dramatically without doubt, in a publicly executed experiment by Jose Delgado. He implanted electrodes into the hypothallamus of bulls reared for bull-fighting. Delgado emphasised that the electrical stimulation quelled the bull's attacks. He had entered the bull-fighting ring, and at the very instant that the bull was about to pounce, Delgado initiated the electric stimulus by pressing a button. The bull stopped in its tracks. Of course, with only one research attempt based upon only one sample head, the drama presented, however, does not constitute scientific proof.
Research into surgically removing specific parts of the brain will also provide clues as to how the emotions are related to these parts. Klüver- Bucy (1939) removed both sides of a monkey's temporal lobes, including the amygdaloid nucleus and the hippocampus.
After surgery some strange behaviour was exhibited by these monkeys. For example, while being clearly afraid of a snake prior to surgery, they became unafraid of the snake after surgery.
This is because those monkeys did not display the normal level of anger they use socially or defensively.
Not only was the behavioural activity exacerbated, but they became imprudent (sexually indiscriminate). They tried to mate with other animals. Then, finally, if there was no 'enticement' they would put not only food but anything, into their mouths.
By removing such brain structures, such monkeys appeared to lose the ability to distinguish between good or bad entirely.
Clinical physicians have reported that the same results are exhibited in patients having illness stemming from damage to their temporal lobes. The behaviour exhibited by a group of such patients is called the "Klüver - Bucy symptom group". For example, one patient who had contracted meningitis had had the temporal lobe and limbic system damaged. Below is an extract from the report upon this patient's behaviour:
This patient seemed to have no awareness of ordinary things. He examined each thing in front of him as if he'd seen it for the first time, repeatedly ng it, but didn't appear to understand its significance. He examined each item he seized by putting it in his mouth. Everything he picked up was put into his mouth, sucking and biting. He ate anything he could lay his hands on. Among such things were plastic bags, cleaning paste and ink. He didn't seem to have any feelings. People and surrounding conditions were seen with no interest (being aroused). Sometimes he became jocular, smile at inappropriate times, and imitated other peoples' gestures and behaviour. He was unable to distinguish appropriate and inappropriate things or conduct. (Marlowe et al, 1975)
One research group (Rosvold,H.E.,Mirsky, A.,F., and Pribram,K.H.1954) removed the amygdaloid nucleus of a red-haired monkey who was a high ranking member of the group. The "boss" monkey whose amygdaloid nucleus had been removed, sank right down to the bottom of the group's "pecking order" when he was returned to the group.
However, this fall in rank was not because of the increased submissiveness, it was on account of the inability to conduct suitable social responses - gestures and 'voice'. This monkey had appeared to have lost the ability to distinguish between good and bad monkey behaviour.
Various reports have been conducted upon the many information exchanges via the interconnection routes between the frontal lobe cortex and between the thallamus and the hypothallamus itself. Because of these, the thoughts of most neural scientists are in agreement over the point that the (frontal cortex works to) "monitor and revise the mechanisms of the limbic system" (Nauta, 1971)
In the 1923 investigation into the 2,000 people having damaged frontal cortex, out of those injured in the first world war, a certain surgeon discovered very many changes in mood (emotions). These ranged from narcissism biased towards curious types of emotions, to melancholy and a failure to plan ahead. Such abnormalities have been confirmed by recent research concerning people who have lost part, or all of their frontal lobe through accident or surgery.
In the case of some patients these personality changes are similar to depression. That is, indifference, loss of spontaneity, a drop in emotional state, and indifference to sex. In a separate patient case, the personality change was akin to the behaviour of a psychiatric patient. In other words, the lack of ability to sense social signs, loss of self-control when conversing. Also a tendency to persist with a particular behaviour arises once having started with this behaviour. That is to say, in spite of needing to respond differently to ambient changes (this sort of patient) will persist with the original reaction (response)
It may be said from the above that peoples' emotions are proven to be intimately related first to the amygdaloid nucleus, and to the cerebral limbic system within the hippocampus and the temporal lobes.
Klüver,H.,P.C.,Bucy.Preliminary analysis of functions of the temporal lobes in monkeys, Arch Neurol Psychiatry 42:979,1939
Rosvold,H.E.,Mirsky, A.,F., and Pribram,K.H.(1954) Influence of amygdalectomy on social behavior in monkey. Journal of Comparative and Phsiological Psychology,47,173-178.