Genetics: Violence as a biological predisposition

1. Genetics: Violence as a biological predisposition 2 constants across cultures: • Men are most likely to commit violent acts. • Sex difference is a universal. • Average man is more aggressive then women even in infancy prior to sex role socialization by adults. • In USA 85% of arrests for violent crimes are men. 2. Young persons are more likely to be violent than older persons

2. Adoption studies • 1,000 boys adopted in Denmark between 1927-1947. • Groups   • 1. Children of criminal Biological Parents adopted to non-criminal parents • 2. non-criminal biological parents adopted by criminal parents • Group 1: were the most likely to be criminals, plus the more extensive criminal history of biological parents the higher risk the child is a criminal. Risk factor was unrelated to whether adopted parents knew of biological parents history or not.

3. Phineas Gage • Railroad Accident – Sept. 1848 • Leveling land with Dynamite • 3 foot inch thick tamping rod was projected in to his brain • Entered via cheek, left Eye and into the frontal lobes • Driven by other workers in a ox-cart to Doctor’s office

4. What happened? • Lost conscious and had convulsion immediately, but awoke quickly and was talking and walking soon afterwards • Never showed any impairment of movement or speech • Memory was intact, and was capable of learning new things • However, within months his personality had changed dramatically • He became extravagant and anti-social, a foul mouth liar with bad manners, frequently got into fights and assaults. • could no longer hold a job or plan his future • According to friends “Gage was no longer Gage”

5. Died after an accident 13 years later • A penniless, epileptic • Harlow (physician who treated him) discussed the link between the frontal damage and behavior change. • 130 years later Antonio Damasio used computer modeling and imaging to determine the path and damage of the tamping rod • The rod damaged the ventromedial frontal lobes. This region is implicated in personality changes and aggression/violence.

6. Implicated Brain structures • Rat lesion studies suggest that different types of aggression may be controlled by different subsets of brain structures. • Limbic sites: amygdala, septum and hypothalamus • Lesion in the Septum of rats • increase predatory aggression but reduce social aggression) • Neural circuit in frontal cortex: medial, frontal and orbitofrontal cortex.

7. Neurobiologist definitions of aggression • Reactive: • This aggression involves unplanned, enraged attacks on the object perceived to be the source of the threat or frustration. • Instrumental: • This aggression is purposeful, goal directed and can be described as cold-blooded (involves executive function)

8. Frontal Cortex • Damage to medial frontal and orbitofrontal cortex is associated with increase risk of reactive aggression in humans. • Neuroimaging studies show evidence of frontal dysfunction in aggressive individuals. • Violent individuals showed significantly less CBF in frontal cortex than comparison individuals. • Neural integrity of prefrontal cortex (proton magnetic resonance spectroscopy (H-MRS) in violent patients showed reductions in N-acetylasparate (NAA-a marker of neural density). (Chritchley, et.al. 2000) • CBF (cerebral blood flow) measured by PET during performance of a continuous performance task in murderers pleading not guilty by reason of insanity and matched comparison individuals was studied. They found that a subset of murders (the reactive murderers vs the instrumental) had lower prefrontal cortex. (Raines, 1997)

9. Amygdala • Possible to increase aggression by modulation of the amygdala. • Electrical stimulation of amgydala increases all types of aggression • Charles Whitman (Austin, Texas University tower mass murder) left a note begging for his brain to be studied. His autopsy revealed he had a tumor pression into his amygdala

10. Neurotransmitters: • Serotonin •  5HT exerts inhibitory control over impulsive aggression • 5HT binding sites in frontal area of alcoholic impulsive violent offenders was lower than in healthy control subjects or non-violent alcoholics. • 5-H IAA reduction in some impulsive offenders with personality disorders • Gene for TPH (tryptophan hydroxalyse) associated with aggressive behavior in males but not females with personality disorders. • 5-ht promotor genes are associated with early onset alcoholism and violent behavior. • 5-HT receptor activation decreased aggression, while those that decrease receptor activation have been found to increase aggression . • Tryptophan depletion increase aggression in both men and women. • Aggressive effect of tryptophan depletion is mediated via the 5-HT1 receptor.

11. -Amiobutyric Acid • Alcohol and benzodiazepines have consistently shown to increase aggression. • Specifically, GABAA receptor complex (receptor agonists benzodiazepines, barbiturates and alcohol.) Increase Cl-flux in ion channel. • Alcohol and Benzo’s heighten aggression effects. • Administration of Benzo’s is associated with increased behavioral aggression following provocation in anxious patients. • Behavioral aggression occurred after one dose of benzodiazepines in normal healthy subjects. • Both alcohol and diazepam affects the lateral orbitofrontal cortex. • Both alcohol and benzodiazpines impair recognition of angry expression in others.

12. Summary of 5-HT and GABA • Both 5-HT and GABA appear to modulate aggression. • 5-HT leads to a suppression of aggression • GABA leads to a increase in the probability of aggression. • However, this is only developed for reactive aggression. • These transmitters have little effect (GABA) and no effect on instrumental aggression.

13. Instrumental aggression which is goal directed behavior requires executive control to implement it. The only transmitters that might modulated the systems crucial for socialization are likely be be related to instrumental aggression. • Norepinephrine • The amygdala is implicated in socialization. NE in amygdala have been implicated in modulation of emotional memory • Some studies show relationship between aggression and increased NE activity. • Beta-adrenergic blocking agents have been used clinically to suppress violent behavior in psychiatric patients • Propanolol in a high dose increase recognition of sadness which is impaired in psychopathic individuals. (they cannot easily process sad expressions).

14. Monoamine Oxadase • Low levels of MAO-A subtype related to increase in violence and aggression • Intergenerational Dutch Family Violence • Men spanning 4 generations • Excessive levels of violence: rapes, assaults, homicides, arson, etc… • 1993: sero tests indicated men were missing MAO-A enzyme (breaks down NE, 5HT, and DA) • Men had excessively high levels of 5-HT

15. Testosterone • In animals, increased levels of testosterone is related to social aggression • reducing testosterone in the alpha male eleminates his dominant social status, and restoring testosterone (through injection) causes him to regain his social status. • However, giving testosterone to non-alpha dominant males does not make them dominant or alpha • So, for animals testosterone does not increase violence or aggresion, but does increase social aggression in alpha males.

16. Humans and testosterone • Abnormally high levels of testosterone in humans is related to increased social aggression, but there is no evidence they are more violent. • Thus, there is no evidence that testosterone levels have any predictive value in identifying violent behavior, nor does it increase violent behavior.

17. Genetics and violent behavior • 1960: researchers looked at men born with an extra Y chromosome. • However, further studies showed while more men in prison had the extra Y then men in the population, they were not necessarily violent. Many were incarcerated for non-violent crime. • Furthermore, XYY males are extremely rare, thus this syndrome could not explain all the violent behavior

18. Genetic mutations studies • Tg-8 knockouts • Blind mice with really lousy tempers • Normally mice with plenty of room can share same environment • Tg-8 mice (who lack MAO-A enzyme) attack any other mice or animal in cage

19. Summary • No specific genes for aggression, perhaps some for impulsivity • Testosterone: no empirical evidence • XYY prisoner study flawed • Amgydala: site of rage • Electrode in bulls • Pre-frontal lobotomies