When Infections Tip Aggression Into Violence
Episode 2, Part 4, Robert Bransfield, MD, connects neural circuits, inflammatory responses to infection, and impulsivity in violent behavior.
Episode 2, part 4, with psychiatrist Robert C Bransfield, MD, focuses on the neurobiology of violence. He explains how aggression and restraint are governed by interacting brain circuits, why excessive fear, poor impulse control, and lack of empathy raise risk, and how infections or injuries can disrupt these systems. He also outlines a biochemical pathway in which chronic inflammation diverts tryptophan away from serotonin toward quinolinic acid, which can promote aggression and suicidality. Bransfield argues for investigating violence as comprehensively as an airplane crash and for taking infection-related drivers seriously in prevention.
“There’s a hierarchy of different circuits. Some circuits say ‘attack and be aggressive,’ and other circuits are ‘restrain,’ and it’s the balance of the two… There’s a difference between healthy aggression and violence. With violence, it goes past the point.”
The Risk Triad: Fear, Impulsivity, Empathy
“In people who are particularly violent, you think of three basic things. One is excessive interpersonal fear. Another is poor impulse control. A third is lack of empathy. Having those three traits puts someone at risk.”
- Impulse control: “We see this a lot in the emergency rooms at two o’clock on Saturday morning after someone has had too much alcohol.”
- Fear/perceived threat: “It could be pathological jealousy, but it is a person seen as a greater threat than they really are.”
- Empathy/bonding: “The temporal lobe, with the amygdala and hippocampus, supports bonding. Your bond to other people allows for normal aggression but stops it at the point of violence.”
When Circuits Are Damaged
“Some people have brain injury. We see it with herpes simplex encephalitis, where there may be damage and some people do not have that empathy or bond.”
“Certain infections may affect the brain, damaging circuits. The same infection may have different effects in different people. Sometimes it is an old infection that left a residual, sometimes it is active or relapsing.”
Biochemical Pathway: Tryptophan, IDO, Quinolinic Acid
“Tryptophan is an essential amino acid that gets converted to serotonin and melatonin. In a proinflammatory state with chronic infection or stress, an enzyme called IDO increases and shifts tryptophan breakdown. Instead of going to serotonin and melatonin, it becomes quinolinic acid. Quinolinic acid is a neurotoxin and an NMDA agonist, and that can make people more aggressive, suicidal, and violent.”
“We need to understand violence the same way we do an airplane crash. A plane does not crash from one failure. Look at all the failures, understand each one, and change the system so those failures do not occur.”
Why Infection Matters for Prevention
“Infection is one of many contributors to violence, and we do not pay enough attention to it. In an era of more advanced weapons and questions about the stability of people in control of them, looking at that connection can help assure peace.”
“We do a great service by working together to understand connections among all causes of violence, including infection, and by connecting the dots to prevent violence.”
Tune into episode 1 of our series, split into 4 parts, for more background context: Rethinking Mental Illness: The Overlooked Impact of Infection
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