This paper examines research into the brain's role in aggressive behavior.
|The Role of Brain Dysfunction in Aggression:
If the body is an intrinsic machine with its various organs playing vital roles in its functioning (i.e., the liver as the filter, the heart as the fuel pump, etc.), then the brain must be the motherboard by which all other organs are controlled. The brain itself serves as a storage unit of information, an interpreter of a complex electrical dialect, and the air-traffic controller responsible for safely, efficiently, and systematically overseeing the "frequent flights" of all the aircraft (or in this case, organs) that call the hanger of the human body home. However, at times this controller can malfunction and ultimately degenerate entirely, thus leading to many rough take-offs and crash landings of these aforementioned aircraft (once again, organs). While too much damage and excessive crashes can lead to closure and abandonment of the air base (i.e., death of the human body), some minor changes in the physiological make-up of the brain can lead to pain, torture, unimaginable evil, and even the death of others. In short, specific damage in localized areas of the brain can lead to what might be considered a "normal" individual into a downward spiral of aggression.
There are several structures and chemicals found within the brain that are linked to aggression. However, for the most part, aggression is not the sole or primary function of those structures or chemicals. Ultimately, aggression is manifested by these structures and chemicals as a byproduct of some type of functional flaw, be it related to physical injury, drugs and alcohol, or defects originating from birth.
Before viewing cases where brain damage or dysfunction has resulted in increased aggressiveness and ultimately death, one must first understand the areas of the brain associated with control of aggression and their designed functions. Several areas of the brain, as well as certain chemicals and hormones, have been linked to aggression. Therefore, if the brain truly pilots human behavior, the amygdala and hypothalamus might be the blades of the propeller that keeps the aircraft from crashing.
The amygdala is a group of neurons found deep within the medial temporal lobes of the brain. It is considered as part of the limbic system and its primary role appears to be in the processing and memory of emotion. It has also been seen as an area of the brain that can directly mediate aggressive attacks. In a study conducted by Potegal et al (1996), it was found that production of Fos protein within the corticomedial amygdala is correlated with increased aggression. Additionally, they showed that producing radiofrequency lesions in the corticomedial amygdala reduced aggression, probably due to lower levels of Fos production. Additionally, in a study involving cats with and without lesions in their amygdala (Zagrodzka et al,1998), it was found that those with lesions to their amygdala did not act aggressively when presented aggression provoking stimuli. Furthermore, when mice were presented before the cats with lesions to their amygdala, they showed uncharacteristic predatory behaviors. However, neither of these findings were the case for those cats without lesions to their amygdala. Zagrodzka and his team did, however, show that by disrupting amygdalar modulation in the hindbrain, a predatory attack-like syndrome could be induced in cats during REM-A sleep.
The hypothalamus is located below the thalamus, just above the brain stem. It is found in the ventral region of the diencephalon. Some of the roles of the hypothalamus include regulation of body temperature, thirst, hunger, and the body's circadian rhythm, or internal clock. The hypothalamus may also serve a regulatory role in aggression. The hypothalamus contains important receptors that help regulate aggression levels based on interactions with neurotransmitters serotonin (an aggression inhibitor) and vasopressin (an aggression agonist). In fact, one study (Ferris et al, 1997) measured the control of aggressive behavior in golden hamsters through interactions of serotonin and vasopressin in the anterior hypothalamus. In their study, the latency of attack in the hamsters was prolonged with administration of serotonin (fluoxetine) and was accelerated with the administration of arginine vasopressin. In another study (Beata, 2001), it is stated that irrational aggression in dogs has been shown to be regulated by the ventromedial hypothalamus.
Blair (2004) connects the functioning of the amygdala and the hypothalamus in aggression in the following manner:
"A circuit has been identified that runs from medial amygdaloidal areas
downward, largely via the stria terminalis to the medial hypothalamus, and
from there to the dorsal half of the periaqueductal gray (PAG). The system
is organized in a hierarchical manner such that aggression evoked from the
amygdala is dependent on functional integrity of the medial hypothalamus
and PAG but that aggression evoked from the PAG is not dependent on
the functional integrity of the amygdala."
Apart from the amygdala and the hypothalamus and their roles in aggression, others areas that might modulate aggressive behavior is the frontal lobe and prefrontal cortex. Damage to these areas might be viewed as losing an engine in a dual-engine jet. As these planes spiral downward, they ultimately take the lives of many innocent passengers. In terms of human behavior, specific brain damage might result in psychopathic behavior, which in turn takes lives of many innocent people. In fact, some of the most notable findings of frontal lobe and prefrontal cortex damage affecting aggressive behavior have been found in cases involving psychopaths.
The psychopath, or sociopath, falls under the diagnosis of Antisocial Personality Disorder (APD) as outlined by the Diagnostic and Statistical Manual of Mental Disorders IV (DSM-IV). According to the DSM-IV, "Antisocial personality disorder is characterized by a lack of regard for the moral or legal standards in the local culture. There is a marked inability to get along with others or abide by societal rules. Individuals with this disorder are sometimes called psychopaths or sociopaths" (Antisocial Personality Disorder: Web Page). Additionally, psychopathy can be viewed as a cluster of interpersonal, affective, and behavioral characteristics, including persuasiveness; impulsivity; poor behavioral controls; shallow affect; and lack of empathy, guilt, and remorse (Kiehl et al, 2006). As noted by Sabbatini (1998), approximately 1% to 4% of the population can be considered sociopathic. Of those with sociopathic characteristics, 47% also have what the researchers deemed significant arrest records. Sabbatini goes on to note research that has stated that over a period of 40 years, studies have suggested that incidences of neuropathology among violent crime offenders as opposed to the general population reaches ratios as high as 31:1 (these cases being of homicide). In addition to Sabbatini's remarks, in 2003, 5,570 individuals between the ages of 10 and 24 were murdered in the United States (Brain Briefings, 2007). These numbers calculate to approximately 15 deaths per day. Additionally, it was noted that, although figures from the United States Department of Justice have shown declining numbers of violent crime victims in recent years, the average individual faces an 80% chance of becoming a victim of a violent crime during his or her lifetime. Numbers like these have lead researchers to ponder the question, "What causes an individual to display psychopathic manifestations?"
One such study conducted by Seidenwurm, Pounds, Globus, and Walk (1997),
showed metabolic abnormalities within the temporal lobe of seven individuals with histories of extremely violent behaviors. Positron emission tomography (PET) with fludeoxyglucose (FDG) F18 was used in the study along with several other evaluations and tests. Ultimately, the abnormalities found by the FDG-PET were correlated with limbic abnormalities seen during electrophysiological and neuropsychiatric evaluations. Most all subjects were found to have organic brain syndrome in relation to the physical abnormalities found within their brains. The following table shows the results of the tests
Subject Age/Sex Index Behavior Other Behavior Psychiatric Diagnosis Neuropsychological
1 33/M Killed four 14-y-old boys Genital self-mutilation Chronic Paranoia, schizophrenia with acute exacerbations Uncooperative
2 20/M Shot police officer Lived in brothel Organic brain syndrome Visual, spatial, memory impairment: impaired problem solving abilities
3 17/M Repeatedly stabbed one person fatally Extremely dependent Organic brain syndrome IQ 71, organic mental disorder
4 29/F Eviscerated mother and daughter Solitary, bizarre, stereotyped motions: exhibitionic behavior Chronic undifferentiated schizophrenia IQ 82, psychotic, no evidence of brain damage
5 17/M Beat and fatally strangled girlfriend Reckless motorcycle rider, death rock music, bizarre dress Antisocial personality disorder, organic brain syndrome, paranoid IQ 84, organic mental disorder, impulsivity, low frustration tolerance
6 39/M Shot policeman during prison escape Boxer Organic brain syndrome, organic personality disorder Frontal, occipitoparietal, and hippocampal abnormalities; reduced intelligence
7 20/M Shot, raped stepmother, hid body in closet Unpredictable violence Organic brain syndrome and adjustment disorder Mild impairment of visual, spatial, and memory processing, R more than L hemisphere
Table 1: Findings of Seidenwurm et al (1997).
When looking at the relative metabolism in the medial temporal lobes of these seven individuals (Table 1), an averaged percentage of decreased activity was 39% (range: 33% to 54%). Additionally, of the six individuals willing and able to cooperate with PET scanning and neuropsychiatric evaluations, five had temporal lobe abnormalities, four of which were focal and one with diffuse cerebral abnormalities. In addition to this research, Blair (2004) has stated that the orbital frontal cortex might also play a role in psychopathic behavior by means of response reversal.
Several other researchers have shown that aggression can be link to specific brain damage or abnormalities, especially within groups of individuals labeled psychopaths. One such study was conducted by Blake, Pincus, and Buckner (1995). In their research, 31 individuals awaiting trial or sentencing for murder or undergoing an appeal received a neurological assessment, including EEG, MRI, and CT scanning. The neurological examination showed evidence of frontal dysfunction in 64.5% of the individuals tested. Temporal lobe abnormalities were noted in 29% of the individuals. Out of 20 individuals that underwent EEG, eight showed abnormalities consisting of bilateral sharp waves with slowing. Nineteen individuals received an MRI or CT, nine of which showed brain atrophy and white matter changes. Blake et al concluded that, "It is likely that prolonged, severe physical abuse, paranoia, and neurological brain dysfunction interact to form the matrix of violent behavior."
In another study (Kiehl et al, 2006), 80 male inmates from a maximum security prison located in Vancouver, British Columbia underwent a videotaped semi-structured interview and an experimental recording session, part of which involved event-related potential (ERP) recording. As a result, electrophysiological data showed the inmates to have aberrant, large, late ERP negativity during target detection. One interpretation made by the team was that the ERPs reflected abnormal cognitive processes associated with target detection. More significantly, another interpretation of the findings suggests that there might be functional or structural abnormalities in the medial and anterolateral aspects of the temporal lobe in the inmates. This suggests that during processing of some linguistic and emotional stimuli, the amygdala and hippocampus are working dysfunctionally.
In yet another study (Gatzke-Kopp et al, 2001) involving 14 murderers, EEG and PET scans were administered to compare findings of what might be seen in EEG but missed in PET. As indicated by increased slow wave activity on the EEG (not apparent on the PET), a deficit in the temporal area was noted. PET findings, however, reported reduced prefrontal, left amygdala, left hippocampus, left angular gyrus, and increased occipital glucose metabolism. In keeping with literature concentrating on violent behavior and frontal or temporal lobe dysfunction, this study also showed dysfunction in these areas for the 14 murderers.
As for individual case studies, one individual whose case might be viewed as that of a psychopath involves Charles Whitman. On August 1, 1966, Whitman shot and killed 14 people, wounding an additional 31 people, from the observation deck of the main building of the University of Texas at Austin. Prior to this massacre, Whitman had brutally murdered his wife and mother. Eventually, Whitman was killed by Austin police. A post mortem autopsy revealed that Whitman had a small brain tumor (The Times, 1966). However, at that time it was noted that the tumor was neither in the vicinity of the brain stem nor frontal lobe. However, with today's medical knowledge, it might very well have played a role in Whitman's aggressive nature.
Another possible example of brain damage leading to aggressive behavior can be found in the case of serial killer John Wayne Gacy. Known as the "Killer Clown," Gacy was convicted of the rape and murder of 33 boys between 1972 and 1978. Of the victims, 29 were found buried in the crawl space beneath his home. However, an examination of Gacy's brain by Dr. Helen Morrison after his execution revealed no physical abnormalities (John Wayne Gacy: Web Page). Despite this, Dr. Morrison did state during Gacy's trail that he had "the emotional makeup of an infant." Furthermore, she noted that the psychological reasons for his crimes might never be revealed. It should be noted, however, that Gacy had suffered a blood clot on his brain that went undiagnosed for more than five years. Some individuals believed that this clot might have produced residual damage to the brain, thus leading to Gacy's psychopathic behavior.
Outside of these studies and examples of psychopaths, some individuals not
necessarily psychopathic in nature can serve as additional case points for the link between brain dysfunction and aggression. These individuals were found to have specific brain damage as well as exhibiting significant negative behavioral changes. In fact, one such case can be dated back to 1848: Phineas Gage.
On September 13, 1848, Phineas Gage was serving as the foreman for a railway construction crew in Vermont. His job entailed that he remove rock from the area by drilling a hole and filling the rock with explosive. As part of this task, he was required to tamp the material into the rock with an iron pipe. Due to direct tamping on the explosive material, sparks ignited the explosives and subsequently sent the iron rod through his left cheekbone, exiting through the top of his skull. Astoundingly, Gage survived the accident.
Dr. Edward Williams responded to the tragedy and later wrote:
"He at that time was sitting in a chair upon the piazza of Mr. Adams'
hotel, in Cavendish. When I drop up, he said, 'Doctor, here is business for
you.' I first noticed the would upon the dead [sic] before I alighted from
my carriage, the pulsations of the brain being very distinct; there was also
an appearance of which, before I examined the head, I could not account
for: the top of the head appeared somewhat like an inverted funnel; this
was owing, I discovered, to the bone being fractured about the opening for
a distance of about two inches in every direction." (Schaffhausen, 1997)
Although he suffered no motor or speech impairments or memory loss, his personality changed in a way such that his family and friends stated they no longer knew him. As Schaffhausen notes, Gage became selfish and displayed bursts of profanity. Furthermore, he became erratic in behavior and unreliable. Ultimately, Gage lost his job with the railway.
Gage's case sparked an interest in research to specify what areas of the brain function in relationship to emotion, including aggression. After Gage's death, his body was exhumed and examined in order to detail the areas of the brain that might have been affected by the accident. After review, it was apparent that the accident caused significant damage to the prefrontal and orbital frontal cortex, areas associated with decision making and temperament. In more recent research, evidence from other patients has supported the notion that the prefrontal and orbital frontal cortex plays an important role in aggressive
A more recent instance of an individual expressing aggressive behavior with a lethal ending can be seen in the case of deceased professional wrestler Chris Benoit. On June 25, 2007, Benoit, his wife, and his seven year old son were found dead in their home. Benoit's case was the result of a murder-suicide. At first, many believed that Benoit's story was a cause of "roid rage." In fact, it was reported that elevated levels of testosterone, which previous research has linked to the emotion of aggression, were found in his body (Chris Benoit: Web Page). However, a report by ABC News (2007) stated that Benoit's brain was examined by Dr. Julian Bailes, head of neurosurgery at West Virginia University. According to Dr. Bailes and his research team, Benoit's brain had suffered such severe damage from years of wrestling and subsequent concussions that it resembled that of an 85-year-old Alzheimer's patient. Furthermore, Dr. Bailes noted that damage was found in all four lobes as well as deep within the brain stem. In support of the idea that such brain damage could lead to uncontrolled aggressive behavior, Dr. Bailes and his research team have also analyzed brains of former NFL players, most notably Andre Waters and Terry Long, each of whom committed suicide. Dr. Bailes team has theorized that multiple concussions can lead to dementia, which can contribute to severe behavioral problems.
Much research and studies have found specific links between aggression and brain dysfunction. Be it brain damage to a specific area or a chemical malfunction within the brain, the slightest of changes can elicit unimaginable acts of aggression. Unfortunately, however, with new ways to alter the brain's functionality gaining popularity in the world each day (i.e., crystal methamphetamine, steroids, human growth hormones, etc.), there appears to be no silver lining on the horizon for the end of brain malfunctions. However, as the medical field and technology continues to advance, hopefully we can expect to hear much less of, "I'm sorry, but we are experiencing some turbulence," and much more of, "Thank you for flying today," (from our pilot "the brain").
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