Understanding & Controlling Aggression

Aggression: Types and Context

• Reactive aggression: aggressive behavior due to feeling threatened or protecting loved ones
• Proactive aggression: deliberately harming others without provocation
• Indirect aggression: non-​​physical aggression, such as shaming

Biological Mechanisms of Aggression

• Different neural circuits, hormones, and neurotransmitters are involved in various types of aggression
• Understanding the biology and psychology of aggression can help in understanding all emotional states

Aggression vs. Sadness

• Pop psychology often claims that aggression is just amplified sadness
• However, peer-​​reviewed literature shows distinct, non-​​overlapping brain circuits for aggression and grief/​​mourning
• Sadness and aggression can coexist, but they are not the same thing

Tools for Controlling Aggression

• Understanding the underlying biology and psychology of aggression can help individuals modulate and control aggressive tendencies
• This understanding can also help people engage with others in a more adaptive way overall
  Biology and Psychology of Aggression
• Conrad Lorenz: studied imprinting behaviors and fixed action patterns 
  • Known for getting geese to believe he was their parent
  • Discovered fixed action patterns: patterns of behavior evoked by a single stimulus
  • Neural circuits, not individual brain areas, are responsible for aggression
  • Aggression is a process, not an event
• Lorenz’s notion of a pressure 
  • Multiple factors can drive someone to be aggressive
  • No single brain area flips the switch for aggression
• Walter Hess: worked on cats to identify brain areas related to aggression 
  • Stimulated different brain areas to observe behavior changes
  • Found that stimulating the ventromedial hypothalamus (VMH) caused aggressive behavior
  • Confirmed in other animals and humans
• Ventromedial hypothalamus (VMH)
  • Small collection of neurons responsible for generating aggressive behavior
  • Activity of neurons in the VMH is necessary and sufficient for aggression
    VMH and Aggression in Psychiatric Disorders
• Ventromedial hypothalamus (VMH) is important in understanding aggression in psychiatric disorders 
  • Schizophrenia, PTSD, depression, borderline personality disorder, and some forms of autism
• Aggression can be adaptive (e.g., maternal aggression) or pathological (harming self or others)

VMH Experiments by David Anderson’s Lab at Caltech

• Identified VMH in mice and analyzed genes/​​proteins expressed in particular cells
• Estrogen receptor-​​containing neurons in VMH responsible for generating aggressive behavior
• Used optogenetics (light-​​triggered electrical activity in neurons) to stimulate estrogen receptor neurons in VMH 
  • Male mouse with female mouse: stimulation caused male to stop mating and attack female
  • Male mouse alone with rubber glove: stimulation caused male to attack glove
  • Stimulation of VMH in male or female mice evokes aggressive behavior

Connections between VMH and Other Brain Areas

• VMH connected to periaqueductal gray nucleus (PAG)
  • PAG houses neurons that create endogenous opioids for pain relief
  • PAG connected to neural circuits controlling biting behavior
• Aggressive biting behavior in humans, especially children, seen as a mark of pathology
  Soccer Incident and Aggression 
• Soccer player bitten by another player 
  • Biting considered primitive and troubling behavior
  • Associated with more primitive circuitry

Neural Circuits and Aggression

• Ventromedial hypothalamus activation triggers aggression 
  • Downstream circuit in periaqueductal gray
  • Fixed action patterns like swinging limbs and biting
• Neural circuits, not individual brain areas, evoke aggression

Testosterone and Aggression

• Testosterone does not increase aggressiveness 
  • Increases proactivity and willingness to lean into effort in competitive scenarios
  • Challenge hypothesis
• Testosterone can increase aggression in already aggressive individuals 
  • Can also increase benevolence and altruism in others
• Testosterone increases competitiveness, not aggression

Estrogen and Aggression

• Activation of estrogen receptor containing neurons triggers aggression 
  • Testosterone converted into estrogen through aromatization
  • Aromatase enzyme converts testosterone into estrogen
• Estrogen, not testosterone, triggers aggression 
  • Testosterone required for conversion into estrogen
• Estrogen’s effect on aggression modulated by day length 
  • Long days: reduced melatonin, increased dopamine, reduced stress hormones 
    • Estrogen increase does not evoke aggression
  • Short days: increased melatonin, stress hormones 
    • Estrogen increase heightens predisposition for aggression
      Shorter Days, Aggression, and Hormones
• Shorter days can lead to increased aggression due to higher stress hormone (cortisol) levels and lower dopamine levels. 
• Higher cortisol and lower serotonin levels can increase the propensity for aggression.
• Estrogen can trigger aggression in both males and females, depending on cortisol levels.

Factors Influencing Aggression

• External stimuli (e.g., upsetting words or actions)
• Internal state (e.g., stress levels, feelings of contentment)
• Cortisol levels (higher levels lead to increased reactivity and aggression)
• Serotonin levels (lower levels can lead to increased aggression)

Tools to Reduce Aggression

• Tryptophan-​​rich diets or supplementation can help increase serotonin levels.
• Omega‑3 fatty acid supplementation can reduce impulsivity and aggressiveness.
• Getting sunlight exposure and managing cortisol levels through heat exposure (e.g., sauna, hot baths) can help reduce aggression.
• Ashwagandha supplementation can decrease cortisol levels, but should not be used for longer than two weeks at a time.
  Reducing Cortisol and Aggressiveness 
• Cortisol reduction can help decrease irritability and aggressive tendencies 
• Genetic predisposition to irritability and aggression exists 
  • Genes code for neural circuits, neurotransmitters, hormones, etc., that shift our biology
  • Estrogen receptor sensitivity can result in increased aggression
  • Photoperiod (day length) can modulate aggressiveness in people with certain gene variants
• Pay attention to how you feel at different times of the year and adjust sunlight exposure accordingly

Testosterone and Aggressiveness

• Testosterone levels in men of different professions 
  • Ministers, salesmen, firemen, professors, physicians, NFL players (lowest to highest testosterone levels)
  • Competitiveness and physical exertion may play a role in testosterone levels
• Testosterone levels in female prisoners 
  • Higher levels of testosterone related to violent crimes and prison rule violations
• Testosterone can have acute effects on aggression pathways 
  • AndroGel study: increased corticomedial amygdala activation 30 minutes after application
  • Testosterone can activate amygdala circuitry for action-​​based states
  • Testosterone makes effort feel good and biases organisms toward leaning into challenges
  • Estrogen activates aggression pathways in the ventromedial hypothalamus
  • Testosterone likely acts to accelerate or bias states of mind and body toward aggression
    Testosterone, Estrogen, and Aggression
• Testosterone increases the pressure towards aggressive episodes 
• Estrogen triggers aggressive episodes in the ventromedial hypothalamus
• Testosterone makes people lean into effort, which can lead to aggression if the effort involves being aggressive

Social Context and Aggression

• Infinite variables determine the social context in which aggression occurs
• Two factors that can bias certain social contexts towards aggression: alcohol and caffeine

Caffeine and Aggression

• Caffeine increases autonomic arousal and alertness
• Increases activity in the sympathetic arm of the autonomic nervous system
• Can increase impulsivity

Alcohol and Aggression

• Alcohol decreases activity in the sympathetic arm of the autonomic nervous system
• Initially increases alertness by inhibiting the forebrain
• Later acts as a sedative, reducing activity in the forebrain and releasing deeper brain circuits involved in impulsivity

Study: Caffeinated and Non-​​Caffeinated Alcohol Use and Indirect Aggression

• Published in the Journal of Addictive Behavior in 2016
• Examined how ingestion of caffeinated or non-​​caffeinated alcohol drinks impacted indirect aggression (verbal acts of aggression)
• Found that heavier caffeinated alcohol beverage use was associated positively with indirect aggression even after considering one’s typical alcohol use and dispositional aggression

Self-​​Regulation and Aggression

• Self-​​regulation is a key feature of whether or not someone will engage in aggressive speech or behavior
• Tools to reduce the probability of aggression can be found in previous episodes

Study: Efficacy of Carnitine in the Treatment of Children with ADHD

• Explored how acetyl-​​L-​​carnitine supplementation could adjust the behavioral tendency of kids with ADHD
• Found a significant effect of acetyl-​​L-​​carnitine supplementation on improving some of the symptomology of ADHD
• Randomized, double-​​blind, placebo-​​controlled, double crossover study
• Conducted on 6 to 13-​​year-​​old kids diagnosed with ADHD
• Acetyl-​​L-​​carnitine dosage was 100 mg per kg, with a maximum dosage of 4 grams per day
• Study duration: 24 weeks, with behavioral outcomes and psychological outcomes measured at weeks 8, 16, and 24
  Carnitine and ADHD 
• Study on children with ADHD given L‑carnitine twice daily 
  • Showed significant reductions in total problem score, attentional problems, delinquency, and aggressive behavior
  • Confirmed shifts in L‑carnitine within the bloodstream of the children
  • Suggests L‑carnitine can be used alongside other supplements and behavioral changes to reduce aggressive tendencies

Dr. David Anderson

• Expert on the neurobiology of aggression
• Author of “The Nature of the Beast: How Emotions Guide Us” 
  • Introduction to the history and current science of emotions
  • Accessible for both scientists and non-scientists