NEURAL MECHANISMS IN AGGRESSION
SPECIFICATION: Neural mechanisms in aggression, including the roles of the limbic system.
The Amygdala and aggression
Key Words
The neocortex is the thinking part of the brain where logic and judgment reside. It is the outer portion of the brain and is divided into lobes. Think of the cortex as the strategy centre of the brain. When someone is experiencing and expressing anger, he or she is not using the thinking (cortex) part of the brain but primarily the limbic centre of the brain.
Limbic system: The limbic system is the emotional centre of the brain. It is located lower in the brain and is considered more primitive than the cortex.
Hypothalamus: a region of the brain, between the thalamus and the midbrain, that functions as the main control centre for the autonomic nervous system by regulating sleep cycles, body temperature, appetite, etc., and that acts as an endocrine gland by producing hormones, including the releasing factors that control the hormonal secretions of the pituitary gland.
Hippocampus: (named after it resembles the seahorse, is a major component of the brains of humans and other vertebrates. Humans and other mammals have two hippocampi on each side of the brain. It belongs to the limbic system and is important for consolidating information from short-term to long-term memory and spatial navigation. The hippocampus is under the neocortex; in primates, it is in the medial temporal lobe, underneath the cortical surface.
Thalamus: is a midline symmetrical structure of two halves within the vertebrate brain, between the neocortex and the midbrain. Its functions include relaying sensory and motor signals to the neocortex and regulating consciousness, sleep, and alertness.
Quick facts:
The Amygdalae (singular: Amygdala; are two almond-shaped groups of nuclei located deep and within the brain's temporal lobes. The Amygdala is a primitive brain structure found in all vertebrates. The Amygdala has been shown in research to perform a primary role in the processing of:
Memory
Decision-making
Emotional responses
THE ROLE OF THE AMYGDALA
The amygdala is part of the limbic system (the limbic system is a group of structures in the brain associated with our emotions and urges).
The Amygdala is the brain area responsible for our “fight or flight” reactions, our natural survival instincts. It is thought to have evolved as the fear response. For vertebrates, fear is an adaptive response, without it animals and humans would walk straight into danger repeatedly and very likely end up dying or at the very least being seriously injured.
The Amygdala forms connections between the neocortex, hypothalamus, hippocampus and thalamus.
The Amygdala is fundamental in controlling emotional responses, while the hippocampus is important in memory and learning. It makes sense that the Amygdala and Hippocampus are connected as we need to learn what to fear; we do not need to assess the same situations continually. Assessing situations for danger takes time, and wasted time could mean not reacting quickly enough and dying.
The Amygdala is also connected to all our senses. It is relevant that the Amygdala receives sensory input from the outside world – through all five senses: sight, smell, hearing, touch, and taste, as well as from the viscera (internal organs). This makes sense if you think about it, as we need to perceive danger from all these areas: we need to sense danger visually, for example, by seeing a tiger. In terms of olfactory, we need to be able to smell danger (for example, by smelling smoke). The Amygdala also receives input from the neocortex. We need our cortex to be connected to the Amygdala so that we can assess a behaviour (e.g. somebody acting psychotic) or a new situation that we have not encountered before.
When sensations associated with danger are integrated into the Amygdala, fear or aggression is thought to occur, depending on how we assess our ability to deal with the situation. When we are in danger, we can only react in a few ways to protect ourselves: fight, flight, freezing or submission. So, depending on our self-efficacy (one's belief in their ability to succeed in specific situations, we will resort to one of these four methods when frightened.
When data coming in from the world around us passes through the Amygdala, the decision is made whether to send the data to the brain's limbic system or the cortex area. Suppose the incoming data triggers enough of an emotional charge (like seeing an axe man in your bedroom at night). In that case, the Amygdala can override the neocortex, which means the data will be sent to the limbic system, causing the person to react with only this part of their brain.
If the Amygdala perceives a memory match to a scary event (stimulus). For example, this is the second time you have seen this scary axe man (the memory of the scary event will have been recorded in the hippocampus. The hippocampus then tells the Amygdala whether to act in a fight, flight, submissive or freeze situation. Moreover, when the memory is stressful and fear-evoking, the Amygdala triggers the HPA (hypothalamic-pituitary-adrenal) axis and hijacks the rational brain.
So, during a really scary event like this, the Amygdala overrides the conscious part of the brain where a person thinks about their situation. The Amygdala goes into action without much regard for the consequences (since this area of the brain is not involved in judging, thinking, or evaluating).
This emotional (limbic) brain activity processes information milliseconds earlier than the rational brain. In case of a memory match of a scary event, the Amygdala acts before any possible direction from the neocortex can be received. So the person acts instinctively without thought!
If the Amygdala does not find any memory match to the stimulus received with its recorded threatening situations, it acts according to the directions received from the frontal cortex. It assesses new situations.
This reactive incident has come to be known as an Amygdala hijacking.
“When animals and humans experience an Amygdala hijack, the emotional part of the brain – the Amygdala – overrides the thinking part of the brain – the frontal/neocortex – in response to a perceived threat. Depending on the degree of hijack, an individual’s ability to reason and think logically is compromised. Their working memory becomes less efficient, and their blood pressure, adrenaline, and hormone levels rise. Once an emotion has been turned on flood of hormones are released that cause physical and emotional alarm. A surge of energy follows, preparing the person for the fight or flight response. The impact of this hormonal flush lasts for several minutes, during which time the person is usually out of control and may say or do things he or she will regret when the thinking part of the brain reengages.
Further, an additional longer-lasting hormone is released. And its impact can last for several hours to several days.”
Once a fear has been learned, it activates without any cognitive assessment. A02: This can explain why children who have learned to fear something trivial as children continue to do so as adults.
Goleman, a psychologist, states that "[e]motions make us pay attention right now — this is urgent - and give us an immediate action plan without having to think twice. The emotional component evolved very early: Do I eat it, or does it eat me?" The emotional response "can take over the rest of the brain in a millisecond if threatened." An Amygdala hijack exhibits three signs: strong emotional reaction, sudden onset, and post-episode realization if the reaction was inappropriate. “
The Amygdala and aggression
In most people, the Amygdala works proficiently and accurately detects fear. Thus, most people will respond to a particular fear appropriately. So, for example, if confronted by a stronger and faster animal, they will submit. If confronted by a less strong animal, they may fight or run.
It is thought that people who are excessively aggressive or fearful have problems with their Amygdala. This can be because their Amygdala is damaged or smaller (see below for research examples).
Damage can occur through stroke, tumour, parasites, rabies, epilepsy or developmental problems (it just did not grow correctly). It has been argued that having a low version of MAOA- an enzyme responsible for mopping excess neurotransmitters (E.g., Dopamine, Noradrenalin and Serotonin- impacts the development of the Amygdala. Foetuses' brains will become flooded with these neurotransmitters during gestation, which may affect brain structures such as the amygdala, making them smaller. Smaller sizes correlate with violent criminals (Wong et al., 1997). Van Elst et al. (2000) showed that temporal epilepsy destroyed 20% of the volume in the Amygdala, and this correlated with aggression in male participants.
But this result can be seen as confusing when we compare this to what we already know about gender differences and Amygdala size. Males generally have bigger Amygdales than females, partly due to high levels of circulating androgens (e.g., testosterone). For example, the Amygdala shrinks by more than 30% in males upon castration.
So, the easy explanation of aggression caused by a large amygdala because males have larger ones is too simplistic. It should be noted, however, that the Amygdala and size were refuted by Muller et al. 2003 who showed that six male psychopaths had high activity as demonstrated in their MRI scans when viewing provocative imagery (high activity/arousal indicative of larger size). Moreover, research has shown that animals show extremely hostile and aggressive behaviour when certain areas of the Amygdala are stimulated so they have high activity/arousal. Arousal of the Amygdala can cause increased aggression in humans. In a human experiment in which a woman's Amygdala was electrically stimulated, she threw a guitar at her psychologist in a rage (Moyer, 1976, 1983).
Aggression could also occur because the Amygdala gets damaged through stroke, rabies, etc., and this damage disrupts or destroys pathways from the Amygdala to other important pathways in the brain, for example, the frontal cortex. This means that aggression may occur because the person cannot correctly assess danger in his cortex and makes catastrophic deductions about normal stimulus (for example, Charles Whitman flew into rages over trivial matters). So, in overtly aggressive responses, it could be that the Amygdala misinterprets information from the senses and cortex and responds incorrectly with overly violent behaviour.
These findings could explain gender differences in aggression as females generally have larger neocortexes than males (the neocortex controls the Amygdala and thinking).
Lastly, it could be people with aggressive tendencies have no fear response, and so they are insensitive to punishment and being scared/worried. Their autonomic nervous system does not respond to stress or fear, so these individuals lash out without fear of retaliation. Research shows (see below) that when rats are lesioned or humans have their Amygdales removed, they stop being afraid of provocative situations and strangers.
Some areas of damage may lead to the Amygdala reacting in an overly aggressive way, others a fearful way, other damage may lead to the Amygdala not reacting to fear.
Research
Research has mainly been focused on five major areas: Ablations and lesions on animals (rats, etc., and in some cases, humans who have shown violent criminal behaviour).
Electrical stimulation of the Amygdala in animals
Case studies of people with tumours in the limbic system and Amygdala.
Patients with temporal lobe epilepsy
Scans of patients with bipolar,
Scans of patients with Rabies,
Scans of patients with MAOA L
Scans of patients with other psychiatric disorders
Scans particularly look for:
Observing size differences in such patients
Observing differences in shape
Observing damage to how the Amygdala connects to other brain regions
Observing how other conditions may affect the Amygdala, Eg. Having MAOA L might mean the excess Serotonin affects the development of the Amygdala in some way.
We are observing size differences in genders.
Observing differences in the left and right Amygdala (lateralisation)
Research findings in brief:
The Amygdala is linked to fear responses and pleasure in humans and other animals.
Research has shown that animals and humans show extremely hostile and aggressive behaviour when certain areas of the Amygdala are stimulated. Arousal of the Amygdala can cause increased aggression in humans. In a human experiment in which a woman's Amygdala was electrically stimulated, she threw a guitar at her psychologist in a rage ((Moyer, 1976, 1983)).
Interesting article see below.
Initially, electrical stimulation of the Amygdala produces sustained attention and orienting reactions. If the stimulation continues, the subject may experience wariness, fear and rage (Cendes et al. 1994). When fear follows the attention response, the pupils dilate, and the subject will cringe, withdraw, and cower. This cowering reaction, in turn, may give way to extreme fear and/or panic such that the animal will attempt to take flight.
Among humans, the fear response is one of the most common expressions of Amygdaloid electrical stimulation and abnormal activation (Davis et al., 1997). Moreover, unlike hypothalamic on/off emotional reactions, attention and fear reactions can last up to several minutes after the stimulation is withdrawn.
In addition to behavioural manifestations of heightened emotionality, Amygdaloid stimulation can result in intense changes in emotional facial expression. This includes crying and facial contortions such as baring teeth, dilation of the pupils, widening or narrowing of the eyelids, flaring of the nostrils, and sniffing, licking, and chewing (Anand & Dua, 1955;). Indeed, some of the behavioural manifestations of a seizure in this vicinity (i.e. temporal lobe epilepsy) typically include throat and mouth movements, including chewing, smacking of the lips, licking, and swallowing--a consequence, perhaps of Amygdala activation of the brainstem which also affects chewing (mastication).
In many instances, patients or animals will react defensively and with anger, irritation, and rage, which seems to gradually build up until the animal or human finally attacks (Egger & Flynn, 1963). Unlike hypothalamic "sham rage" " amygdaloid activation results in attacks directed at something real or, in the absence of an actual stimulus, at something imaginary. There have been reported instances of patients suddenly lashing out and even attempting to attack those close by while amid a temporal lobe seizure (Saint-Hilaire et al., 1980) and attacking, kicking, and destroying furniture and other objects (Ashford et al., 1980).
In addition to sustained electrophysiological activity, the Amygdala is heavily involved in maintaining behavioural responsiveness even without an immediately concrete or visible objective or stimulus (O'Keefe & Bouma, 1969). This includes motivating the organism to seek hidden objects or continue a certain activity in anticipation of achieving a particular long-term goal. At a more immediate level, the Amygdala is probably very important in object permanence (i.e., keeping an object in mind when it is no longer visible) and concrete or abstract anticipation. Anticipation is, of course, very important in the prolongation of emotional states such as fear or anger, as well as the generation of more complex emotions such as anxiety. In this regard, the Amygdala is probably important regarding emotion and maintaining mood states.
Fear and rage reactions have also been triggered in humans following depth electrode stimulation of the Amygdala (Chapman, 1960). Mark et al. (1972) describe one female patient who, following Amygdaloid stimulation, became irritable and angry and then enraged. Her lips retracted, there was extreme facial grimacing, threatening behaviour, and then rage and attack--all of which persisted well beyond stimulus termination.
Similarly, Schiff et al. (1982) describe a man who developed intractable aggression following a head injury and damage (determined via depth electrode) to the Amygdala (i.e. abnormal electrical activity). Subsequently, he became easily enraged, sexually preoccupied (although sexually hypoactive), and developed hyper-religiosity and pseudo-mystical ideas. Tumors invading the Amygdala have been reported to trigger rage attacks (Sweet et al., 1960; Vonderache, 1940).
Several studies have found that the size of the Amygdala is reduced in criminals with violent tendencies (e.g., Wong et al., 1997).
In a study of aggressive patients with temporal lobe epilepsy, Van Elst et al. (2000) found that the Amygdala had lost 20% of its volume.
Whilst lesioning the Amygdala provokes a more submissive response. Lesioning the Amygdala has a 'taming' effect in animals. The Kluver-Bucy Syndrome 1939 demonstrated that the bilateral lesioning of the Amygdala led to hypersexuality, hyperorality, and loss of anger or fear responses.
Complete removal of the Amygdala in rats shows that they have no fear response whatsoever and will continually walk into danger.
The main evidence that the Amygdala causes aggression comes from people who were previously violent and underwent behavioural surgery. This is known as stereotactic Amygdalotomy for intractable aggression. Initially, the procedure was offered to patients suffering from epilepsy or EEG abnormality in addition to aggressive behaviour. Still, eventually, it was offered more broadly to patients suffering from “intractable aggression.” Following this initial report, several other authors reported their outcomes for treating aggression, and over a thousand cases have been studied. The overall symptom improvement was reported to range between 33 and 100%, with most authors reporting 70-85% improvement. A02: Although an Amygdalotomy reduces violent human behaviour - the side effect - is loss of emotion. Is it moral to interfere with somebody’s brain?
The Amygdala’s size is positively correlated with aggressive behaviour across species.
The Amygdala shrinks by more than 30% in males upon castration.
10. Recent research suggests that parasites, particularly toxoplasma, form cysts in the brains of rats, often taking up residence in the amygdala. This may provide clues as to how specific parasites may contribute to the development of disorders, including paranoia.
Animal studies have shown that stimulating the Amygdala appears to increase both sexual and aggressive behaviour. Likewise, studies using brain lesions have shown that harm to the Amygdala may produce the opposite effect. Thus, this part of the brain may play a role in displaying and modulating aggression.
Temporal lobe epilepsy - which involves the Amygdala - can involve violent behaviour.
Rabies is caused by a virus that damages the temporal lobe. Rabid animals are violently aggressive.
Amygdalotomy can disrupt dominance hierarchies in monkeys - Pribram, 1962.
Autopsies of Charles Whitman, who carried out a sniper attack from the University Tower in Texas in 1966, showed he had a tumour pressing on his Amygdala.
There are functional differences between the right and left Amygdala (lateralisation). In one study, electrical stimulations of the right Amygdala induced negative emotions, especially fear and sadness. In contrast, stimulation of the left Amygdala induced pleasant (happiness) or unpleasant (fear, anxiety, sadness) emotions. Other evidence suggests that the left Amygdala plays a role in the brain's reward system so that it may play a part in addiction.
Sex differences: In humans, it is the most sexually dimorphic brain structure *, e.g. males and females have very different Amygdalae. The Amygdala is one of the best-understood brain regions about differences between the sexes. Larger male than female Amygdalae have been demonstrated in children ages 7–11, adult humans, and adult rats. In addition to size, other differences between men and women exist in the Amygdala. Subjects' Amygdala activation was observed when watching a horror film. The study results showed a different lateralization of the Amygdala in men and women. Enhanced memory for the film was related to enhanced activity of the left, but not the right, Amygdala in women. In contrast, it was related to enhanced activity of the right, but not the left, Amygdala in men. One study found evidence that, on average, women tend to retain stronger memories of emotional events than men. The right Amygdala is also linked to taking action and
negative emotions, which may help explain why males tend to respond physically to emotionally stressful stimuli. The left Amygdala allows for the recall of details. Still, it also results in more thought rather than action in response to emotionally stressful stimuli, which may explain the absence of physical response in women.
The Amygdala appears capable of triggering and steering hypothalamic activity and acting on higher-level neocortical processes so that individuals form emotional ideas. Indeed, the Amygdala can overwhelm the neocortex and the rest of the brain so that the person not only forms emotional ideas but responds to them, sometimes with vicious, horrifying results. A famous example of this is Charles Whitman, who in 1966 climbed a tower at the University of Texas and began to kill people with a rifle Case. indiscriminately
Study in Amygdala-Aggression: Charles Whitman
Charles Whitman was born on June 24, 1941, and even before entering grade school, he had shown exceptional intellectual promise, was well-liked by neighbours and had already shown some mastery of the piano, which he "loved to play." At the age of six he was administered the Stanford Binet tests of intellectual ability and obtained an IQ of 138; thus scoring at the 99.9% rank. He also became enamoured by guns; his father was described as a gun fanatic. According to his father, "Charlie could plug a squirrel in the eye by the time he was sixteen." However, Charlie loved animals, was somewhat religiously oriented as a child, was very athletic, was described as "handsome" and "fun" and "high spirited" and was in many respects the "all American boy." He became an Eagle Scout at age 12 and received national recognition as the world's youngest Eagle Scout. Within 15 months, he had earned 21 merit badges. While in high school he continued these activities, pitching for the baseball team and managing the football team. After high school, he joined the Marines and was described as "the kind of guy you would want around if you went into combat." While in the Marines, he got married, and it was during this period that he began to show the first subtle signs that something might be amiss.
He began having occasional bursts of anger. He threatened to "kick the teeth out" of another Marine, was court marshalled, consigned to the brig for 30 days, and reduced in rank. He also began taking copious notes and developed what is referred to as "hypergraphia" excessive writing--a disturbance associated with the Amygdala (Joseph, 1999b).
Incessantly he began to write and leave himself notes, ranging from the mundane to the tremendous love he felt for his wife. "I received a call from Kathy... it was fabulous; she sounds so wonderful. I love her so much... I will love her to the day I die. She is the best thing I have in life. My Most Precious Possession."
Increasingly, however, he was having trouble with his temper and composed notes offering self-advice to control his growing temper and rage attacks. "CONTROL your anger," he wrote, "Don't let it prove you the fool. SMILE--It’s contagious. DON'T be belligerent. STOP cursing. CONTROL your passion; DON'T LET IT lead YOU."
On February 4, 1964, he purchased a diary. According to Charles: "I opened this diary of my daily events as a result of the peace of mind or release of feelings that I experienced when I started making notes of my daily events...."
Nevertheless, he also continued to excel. Although he had been Court marshalled, he also won a scholarship to attend the University of Texas and classes while still in the Marines. He also became increasingly religious and would often have discussions with his schoolmates about the nature of God--hyper-religiousness also being associated with an abnormality involving the Amygdala. Although he was attending classes, he also began to perform volunteer work while simultaneously holding a part-time job, and at times felt overwhelmed with energy, almost manic--mania also being associated with the Amygdala (Strakowski et al., 1999) as well as the frontal lobes (Joseph, 1986a, 1988a, 1999a). And he continued to be well-liked and admired. His supervisor at the bank, E. R. Hendricks, described Charles "as a truly outstanding person. Very likeable. Neat. Nice looking... A great guy."
However, Charles also began suffering terrible headaches, and one day, he lost his temper in class, pulling a male student bodily from his chair and tossing him from the classroom. He felt considerable remorse. He also continued to have frequent bouts of anger and, on occasion, difficulty concentrating and was beginning to overeat--increased food consumption associated with a disturbance of the hypothalamus. Moreover, he began having periods where he couldn't sleep for days at a time--yet another disturbance associated with the hypothalamus, a major sleep centre. Charles also realized that something was wrong and continued writing copious notes to himself, reminding himself to be nice, to control his appetite, and especially to control his temper. But his temper was getting out of control, and Charles was gaining weight.
A close friend, Elaine Fuess, also noticed that something was amiss. "Even when he looked perfectly normal, he gave you the feeling of trying to control something in himself. He knew he had a temper, and he hated this in himself. He hated the idea of cruelty in himself and tried to suppress it."
Charles Whitman finally sought professional help and consulted a staff psychiatrist at the University of Texas Health Center about his periodic and uncontrollable violent impulses. Charles was referred to Dr. Heatly. According to the report written by Dr. Heatly about his session with Whitman, a report which was distributed to the media: "This massive, muscular youth seemed to be oozing with hostility as he initiated the hour with the statement that something was happening to him and he didn't seem to be himself...." Whitman "could talk for long periods, develop overt hostility while talking, and then show signs of weeping during the same narration... History revealed a youth who grew up in Florida, where his father was a successful plumbing contractor and achieved considerable wealth. He identified his father as being brutal, domineering, and extremely demanding of the other three members of the family." Whitman "married four or five years ago, and served a hitch in the Marines.... He referred to several commendable achievements during his Marine service, but also referred to a court martial for fighting, which resulted in being reduced several grades to private. Despite this, he received a scholarship to attend the University for two years and remained a Marine at the same time... He expressed himself as being very fond of his wife but admitted that he had on two occasions assaulted his wife physically. He said he has intensely tried to avoid losing his temper with her... His real concern is with himself at the present moment. He readily admits having overwhelming periods of hostility with a very minimum of provocation... he... also... made explicit reference to thinking about going up on the tower with a deer rifle and shooting people. ....He was told to make an appointment for the same day next week."
Instead, Charles decided to climb the tower and begin killing people. But not before first contacting the police and asking to be arrested. As Charles had not committed a crime, the desk sergeant instead suggested that he see a psychiatrist.
Several days before climbing the tower, Charles Whitman wrote himself a letter:
"I don't quite understand what compels me to type this letter... I don't understand myself these days... Lately, I have been a victim of many unusual and irrational thoughts. These thoughts constantly recur, requiring a tremendous mental effort to concentrate. I consulted Dr Cochrum at the University Health Center and asked him to recommend someone that I could consult about some psychiatric disorders I felt I had... I talked to a doctor once for about two hours and tried to convey to him my fears that I felt overcome by overwhelming violent impulses. After one session I never saw the Doctor again, and since then I have been fighting my mental turmoil alone, seemingly to no avail. After my death, I wish that an autopsy would be performed to see if there is any visible physical disorder. I have had tremendous headaches in the past and have consumed two large bottles of Excedrin in the past three months."
On August 1, 1966, one day before climbing the University of Texas tower, Charles Whitman visited his mother, who greeted him outside her penthouse and introduced him to the night watchman who noticed that Charles was carrying a big black attache case. According to police reports, Charles must have immediately attacked his mother after they entered the penthouse and then brutally beat, strangled, and stabbed her to death, crushing the back of her head, smashing her hands, and stabbing her in the chest with a huge hunting knife.
Later, neighbours told police that they only heard a "child crying and whimpering," which they found puzzling as no child lived in the penthouse.
After brutally murdering his mother, Charles cleaned up the mess and placed her in bed with a notepad lying across and covering up the massive wound in her chest. Charles had left a note. It read: "To Whom It May Concern: I have just taken my mother's life. I am very upset over having done it. However, if there is a heaven, she is there now... I am truly sorry... Let there be no doubt that I loved this woman with all my heart."
After killing his mother, Charles returned home, planning on killing his wife "as painlessly as possible.," as he explained in yet another note: "It was after much thought that I decided to kill my wife, Kathy, tonight...I love her dearly; she has been a fine wife to me as any man could ever hope to have. I cannot rationally pinpoint any specific reason for doing this..." She was sleeping, and after removing the blankets to expose her nude body, he viciously stabbed her repeatedly with his huge hunting knife, leaving five gaping holes in her chest. She died instantly.
Charles wrote another note, which he left with the body: "I imagine it appears that I brutally killed both of my loved ones. I was only trying to do a quick, thorough job... If my life insurance policy is valid, please pay off my debts... donate the rest anonymously to a mental health foundation. Maybe research can prevent further tragedies of this type." And then he added a postscript beneath his signature: "Give our dog to my in-laws. Tell them Kathy loved "Schoci" very much."
The next morning, Charles Whitman climbed the University tower carrying several guns, a sawed-off shotgun, and a high-powered hunting rifle. For the next 90 minutes, he shot at everything that moved, killing 14 and wounding 38.
Post-mortem autopsy of his brain revealed a glioblastoma multiforme tumour the size of a walnut, erupting from beneath the thalamus, impacting the hypothalamus, extending into the temporal lobe and compressing the Amygdaloid nucleus (Charles J. Whitman Catastrophe, Medical Aspects. Report to Governor, 9/8/66).
Commentary and IDAS
Researchers are still not sure which area of the Amygdala is important. The role of the Amygdala is complex. Some studies report that Amygdalotomy increases aggression; others report that it has a taming effect. The Amygdala may modulate output from the hypothalamus. Eggar & Flynn found that (1) attack behaviour produced by stimulating the hypothalamus can be inhibited by stimulating the basomedial nucleus of the Amygdala. (2) Attack behaviour produced by stimulating the hypothalamus can be facilitated by stimulating the lateral nucleus of the Amygdala.
Fear and its emotional memories are not the only things the Amygdala controls. The Amygdala has up to 22 distinct regions, and only two have been implicated in fear. We know so little.
Indeed, aggression is not the only condition linked to the Amygdala. Conditions such as anxiety, autism, depression, post-traumatic stress disorder, and phobias are suspected of being linked to abnormal functioning of the Amygdala due to damage, developmental problems, or neurotransmitter imbalance. What abnormal functioning leads to what behaviour and if this influences other behaviours is not yet understood. EG, depression could lead to aggression.
The role of the neo cortex is especially important in aggression as PET scans to be dysfunctional in many murderers. The Amygdala is connected to the neocortex. More research is needed on how the two affect each other and how problems in one can cause deficiencies and malfunctions in the other.
Indeed, concentrating on the Amygdala alone is reductionist. What is the neuroanatomical of aggressive behaviour? Scientists have linked at least 38 different brain parts to various behaviours considered aggressive. How do they connect? Perhaps it is only a matter of time to prove that brain and the organic substances in the brain equal behaviour. Perhaps with more sophisticated knowledge of the mechanism of the brain and nervous system, one could pinpoint to exact biological causes of behaviour, see and truly understand the "organization of neurons", if not the particular properties of neurons. Other psychologists believe that researchers are still far away from understanding the role of how the brain affects aggression. Most of the results and claims have been numerous and vague.
Despite the wealth of brain region involved aggression is probably best understood with an eclectic approach that combines nature and nurture (see other aggression topics). Indeed a combination of many factors: learning theory, deindividuation, crowding, Testosterone, MAOA L, culture are all probably contributory.
Being aware that a lot goes on physiologically when we get angry like an Amygdala hijack can help us as we deal with our anger or someone else’s. When we know someone is “Amygdala hijacked,” we should give him or her some time (over 20 minutes) before attempting to resolve or discuss what happened because it takes about that long for hormonal releases to decrease in intensity. This could prevent fights, domestic situations or arguments escalating.
Having a long-lasting hormone in the body can explain why someone has an initial, powerful angry reaction, then seems to calm, but later has a huge flair-up disproportionate to the situation because of some small incident occurring while the hormone was active in the bloodstream.
While an overactive Amygdala serves a useful purpose when faced with a genuine physical threat (when emotions and reactions are crucial), it can cause problems when faced with an emotional threat as it can lead that person to react irrationally and destructively.
Determinist: No choice but to react violently if you have a damaged Amygdala. Charles Whitman is a great testimony to this debate as his diaries document his struggle in combating his violent urges despite his best intentions.
This leads to a discussion about whether people with such problems are indeed responsible for their actions and should be sentenced to death and or sentenced to prison.
Does not blame the individual or parents but people may still be stigmatised you may not want to live with someone or bear their children if they had this problem.
Animal studies (are they comparable? Chimpanzees and humans are the only species in which groups of males hunt and kill members of their species. In the Scientific American Frontiers video (2001) "Chimps Observed", is work on rats justifiable?
Case studies and generalsibility. Charles Whitman and the electrical stimulation on humans are case studies and have generalisability issues because there are only a few individuals. Case studies affect the usefulness of the research as the target population must represent those most likely to turn to crime, so if the sample is limited, it will be low in usefulness. Sweet et al. carried out a case study on Whitman who had a tumour that had destroyed the limbic system suggesting this caused the violence. This suggests that as the generalisability is low due to a very restricted sample, it is impossible to show that a damaged limbic system causes all violence. Therefore, the research is less useful in explaining why people turn to crime. But on the other hand a limited sample means that it is possible to rule out other factors that could be studied in depth making the data more valid. Overall this means that any research using small samples needs to be examined carefully as all potential factors that could cause crime must be examined to ensure the research is useful.
Gender: Amygdala theories started as beta-biased with no real distinction between the genders. Yet Over 80% of homicides are committed by men. Most of the victims are also men. This sex difference is found across all cultures. Criminal violence is most likely between the ages of 14 and 24. This shows that murder is not a unique 'culturally determined' human behaviour. Current research on amygdalae is now showing that there are very distinct gender differences in Amygdala (see above). Therefore the theory should be Alpha biased as it can explain gender differences in aggression as females have a bigger pre neo cortex. It is thought that the neo-cortex controls the Amygdala.
Research has mainly concentrated on the neurotransmitters and the limbic area of the brain, which houses the Amygdala, an important area in controlling emotions such as fear and anger. For example, Amygdalotomy cases reduce violent behaviour in individuals but with the side effect of loss of emotion. Temporal lobe epilepsy, which involves the Amygdala, can involve aggressive behaviour. However, problems arise regarding the actual area of aggression and the brain.
What, then, can one conclude about theories seeking to pinpoint and scientifically explain behaviour such as violence and aggression? It is suggested that despite the recurring belief in neurobiology that "brain = behaviour", it is currently too difficult to prove this claim using aggression as an example. Sophisticated measures are necessary to take a step further to explain behaviour fully.
Many researchers think the Amygdala plays a protective role rather than a key role in aggression. "It is a very old brain structure, probably very early on in Phylogeny, [it] was primarily involved in protecting organisms, moving them away from obnoxious chemical situations. As organisms evolved, they got different kinds of sensory information to evaluate stimuli in the environment, and that's one of the reasons why it's more highly connected with the neocortex as organisms evolved. It's getting more high-level information to interpret what's happening in the environment."
ECOLOGICAL THEORIES OF AGGRESSION
ANIMAL MODELS OF AGGRESSION
Several animal models have been used to study the effects of internal states which drugs, hormones and brain lesions can manipulate on aggressive behaviours.
Muricide (mouse-killing) by cats (abandoned for ethical reasons)
Shock-elicited fighting (abandoned for ethical reasons)
Isolation-induced aggression
Resident-intruder aggression
Maternal aggression
Brain-stimulation-induced aggression (hypothalamus)
Dominance-related behaviours in primates
