Understanding & Controlling Aggression

High-Level Overview

In this Essentials episode, Andrew Huberman takes on aggression: what it is biologically, which brain circuits and hormones produce it, and what can be done to dial it down (or, where adaptive, up). He distinguishes reactive aggression, like protecting yourself or loved ones, from proactive aggression, deliberately setting out to harm others, and from indirect aggression such as shaming, noting that each has distinct biological mechanisms. Along the way he takes aim at two popular myths: that aggression is just amplified sadness, and that testosterone makes people aggressive.

The tone is explanatory and occasionally wry, with Huberman walking listeners through striking animal experiments, from a purring cat thrown into a rage by brain stimulation to a mouse that switches from mating to attacking at the press of a button. The conversation moves from classic ethology to modern circuit neuroscience, then to hormones, seasons and stress, and finishes with practical tools: sunlight, heat, ashwagandha and a study of acetyl-L-carnitine in children with ADHD.

The Discussion Explores:

• The types of aggression and why context determines whether it is adaptive
• Why aggression is not a form of sadness, and why irritability and aggression differ
• Konrad Lorenz's hydraulic pressure model and aggression as a process with a beginning, middle and end
• The ventromedial hypothalamus and the estrogen receptor neurons that trigger attack
• Downstream circuits for pain relief, biting and striking
• Why testosterone boosts competitiveness, while estrogen in the brain drives aggression
• How day length, cortisol and serotonin tilt the system toward or away from aggression
• Tools: sunlight, sauna or hot baths, ashwagandha cycling, and acetyl-L-carnitine in ADHD

Deep Dive into Main Ideas

Types of Aggression and a Myth About Sadness

Huberman begins by noting that the context of aggression matters enormously. A mother protecting her children is showing adaptive aggression; unprovoked violence toward another person makes most of us cringe and can even provoke aggression in observers. He then addresses a pop-psychology idea he says does not come from formal academic psychology: that aggression is simply amplified sadness. According to the peer-reviewed literature, nothing could be further from the truth. The brain has distinct, non-overlapping circuits for aggression and for grief and mourning.

You can certainly be sad and aggressive at the same time, he says, but they are not the same thing, and neither are irritability and aggression. Understanding these distinctions, he argues, puts you in a better position to use the tools that reduce, eliminate or, when adaptive, modulate aggression.

Lorenz's Hydraulic Pressure and Aggression as a Verb

The name most associated with the formal study of aggression is Konrad Lorenz, who studied imprinting and fixed action patterns, whole categories of behavior triggered by a single stimulus. The implication, which turned out to be true, is that neural circuits, collections of brain areas working in sequence like keys played on a piano, generate these behavioral patterns. That means, in Huberman's words, "aggression is a verb": it has a beginning, a middle and an end, a process rather than an event, which matters for thinking about how to halt it before it starts or prolong it when needed.

Lorenz knew little about neural circuits, but he proposed that many factors, hormones, neurotransmitter states and childhood history among them, build up a kind of hydraulic pressure, like fluid pushed into a container until it is ready to burst. Huberman says this is exactly how the system works: no single switch flips aggression on, and low pressure can keep someone non-reactive or even passive. You can learn to notice this veering toward aggression, verbal or physical, in yourself and others.

The Ventromedial Hypothalamus: A Small Hub for Rage

The first experiments locating aggression in the brain came from Walter Hess, who worked on awake cats at a time when most labs used cats or rats. Since the brain has no pain sensors, he could lower stimulating electrodes through a small hole in the skull. At one site, stimulation turned a passive, purring cat into a creature in absolute rage, and within seconds of switching it off, the cat was calm again. Later work in mice and humans showed that stimulating the same area evokes not just aggressive behavior but subjective feelings of anger. That area is the ventromedial hypothalamus (VMH), a nucleus of only about 1,500 neurons on each side of the brain.

David Anderson's lab at Caltech showed the VMH is both necessary and sufficient for aggression, and identified a specific group of VMH neurons that express an estrogen receptor as the key population. Using optogenetic tools developed by Huberman's Stanford colleague Karl Deisseroth, researcher Dayu Lin, now running her own lab at New York University, placed a thin fiber optic cable into the mouse hypothalamus so blue light could activate just those neurons. In one experiment, a male mouse mid-mating with a receptive female immediately stopped and tried to kill her when the light came on, then went back to mating when it was switched off. In another, a male alone in a cage attacked an inflated rubber glove as though it were another animal whenever the neurons were stimulated. The shifts happened within seconds, if not milliseconds.

Downstream Circuits: Pain Relief, Biting and Striking

Lin's later work shows the VMH connects to the periaqueductal gray (PAG), a structure in the back of the brain that contains neurons capable of producing the body's own opioids for pain relief, which makes sense in a circuit for aggression, since even an aggressor may get hurt. The PAG also connects, through several processing stations, to circuits controlling the jaw, and stimulating the VMH can evoke aggressive biting.

Huberman notes that biting as aggression usually disappears early in childhood, and when it doesn't, it's generally seen as a sign of pathology. The PAG triggers a set of fixed action patterns including biting and swinging the limbs in uncontrolled punching, using the same mouth and limbs we otherwise use to sing, kiss, eat or gesture. His takeaway: "neural circuits, not individual brain areas, evoke the constellation of behaviors that we call aggression."

Estrogen, Not Testosterone, Drives Aggression

That these aggression neurons carry estrogen receptors, and trigger aggression in both males and females, against both sexes, seems puzzling. Huberman sets out to dispel a common myth: "testosterone does not increase aggressiveness." Instead, testosterone increases proactivity, competitiveness and willingness to lean into effort. If someone is already aggressive, testosterone may make them more so; if someone is benevolent and altruistic, it tends to make them more benevolent and altruistic, at least up to a point.

The explanation is aromatization: the enzyme aromatase converts testosterone into estrogen within the brain, and that estrogen binding to the VMH's estrogen receptor neurons is what triggers aggression. "It is not testosterone itself that triggers aggression." Mice or humans lacking aromatase show reduced aggression no matter how high their testosterone. In males, who have relatively less circulating estrogen, testosterone is required as the raw material; females generally already have enough estrogen present to activate the circuit. So both sexes are primed for aggression, but whether it is expressed depends on context.

Day Length, Cortisol and Serotonin Set the Context

One powerful context is day length. Long, sunny days, with light reaching the eyes and skin, reduce melatonin, increase dopamine and lower cortisol and other stress hormones. Under those conditions, experimentally raising estrogen does not produce aggression. In short days, when melatonin circulates longer, dopamine is lower and stress hormones are higher (winter also brings more bacteria and viruses, which survive better in the cold), raising estrogen does increase the predisposition to aggression.

The common thread is that high cortisol and low serotonin, the neuromodulator linked to well-being and sometimes mild passivity, make it more likely that estrogen will trigger aggression, increasing Lorenz's hydraulic pressure. External events, like someone saying something upsetting, combine with internal state, including stress and feelings about whether we have enough, to determine whether we strike back or hold off. High cortisol and adrenaline push the autonomic nervous system toward its sympathetic, ready-to-act side, even producing a low-level anticipatory tremor, since a body in motion is more easily set into further motion.

Tools to Lower Cortisol and Aggressive Drive

Huberman's first tool is sunlight: get it in your eyes early in the day and as much as you safely can throughout the day, which helps keep cortisol in a healthy range. Second, heat: a 20-minute sauna at 80 to 100 degrees Celsius, or a hot bath if you lack a sauna, can reduce cortisol, with details covered in his earlier episode on heat.

Third, for those interested in supplements, ashwagandha is the chief player for potently lowering cortisol. He advises checking with a doctor first and warns that it can disrupt other hormone and neurotransmitter pathways, so he suggests using it for about two weeks and then taking a two-week break rather than using it chronically. It may be helpful during a period of increased irritability and aggression, especially when light exposure is low or circumstances are stressful.

Genes, Seasons and an ADHD Study

Some people carry a genetic variant that changes their estrogen receptor sensitivity and can make them considerably more irritable and aggressive. But even here, day length is a strong modulator. Huberman cites a paper by Trainor and colleagues in the Proceedings of the National Academy of Sciences titled "photo period reverses the effects of estrogens on male aggression via genomic and non-genomic pathways", as evidence that genes and environment interact. Since most people don't know whether they carry the variant, he suggests paying attention to how you feel across seasons and conditions, for example during long summer stretches spent indoors under fluorescent light late in the evening.

Finally, he describes a randomized, double-blind, placebo-controlled, double crossover study titled "efficacy of carnitine in the treatment of children with attention deficit hyperactivity disorder", which tested acetyl-L-carnitine supplementation. It produced significant reductions in the total problem score, attention problems, delinquency and, most relevant here, aggressive behavior, and researchers confirmed the change in carnitine levels in the children's blood. His broader point is that no single supplement, diet change or behavior will transform someone, but combining behavior, attention to season and stress, diet and supplementation can relieve some of the internal pressure toward aggressive impulsivity.

Conclusion

Huberman's picture of aggression is of a circuit-driven process, not a switch or a disguised form of sadness. A tiny group of estrogen receptor neurons in the ventromedial hypothalamus, fed by testosterone converted into estrogen in the brain, can unleash attack, biting and striking through downstream circuits. Whether that happens depends on the buildup of Lorenz's hydraulic pressure: high cortisol, low serotonin, short days and certain genetic variants push toward aggression, while ample sunlight, lower stress and a calmer internal state push away from it. The practical tools follow directly: get sunlight throughout the day, use sauna or hot baths to lower cortisol, consider short cycles of ashwagandha with a doctor's input, and recognize that for some, such as children with ADHD, acetyl-L-carnitine has shown promise. Understanding aggression this way, he suggests, makes it easier to recognize in others and to manage in ourselves.

This is a summary of "Understanding & Controlling Aggression" from Huberman Lab, giving you the GIST so you can decide if you want the REST. Listen to the full episode.