Chapter 1: What are the different types of aggression discussed?
Welcome to Huberman Lab Essentials, where we revisit past episodes for the most potent and actionable science-based tools for mental health, physical health, and performance. I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. Today, we are discussing aggression.
I'm going to explain to you that there are several different types of aggression. For instance, reactive aggression versus proactive aggression, meaning sometimes people will be aggressive because they feel threatened or they are protecting those that they love who also feel threatened. There's also proactive aggression where people go out of their way to deliberately try and harm others.
And there is indirect aggression, which is aggression not involving physical violence. For instance, shaming people and things of that sort. It turns out that there are different biological mechanisms underlying each of the different types of aggression. And today I will define those for you.
I'll talk about the neural circuits in the brain and body that mediate each of the different kinds of aggression. Talk about some of the hormones and peptides and neurotransmitters involved. I promise to make it all accessible to you, even if you do not have any biology or science background.
I'm certain that by the end of the episode, you will come away with a much more thorough understanding of what this thing that we call aggression really is. And when you see it in other people, I think it will make more sense to you. And when you observe it in yourself or the impulse to engage in aggression, verbal or physical or otherwise, I hope that you'll understand it better as well.
And of course, the tools that I will describe should allow you to modulate and control aggressive tendencies or predispositions to aggressiveness, and just generally be able to engage with people in a more adaptive way overall. The context of aggression really matters.
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Chapter 2: How do hormones like estrogen and testosterone influence aggression?
So there are instances where aggression is adaptive, for instance, a mother protecting her children. Of course, other forms of aggression like unprovoked proactive aggression, somebody simply being violent to somebody else, even when unprovoked.
Chapter 3: What role does sunlight and seasonal changes play in aggression?
Most of us cringe when we see that kind of behavior. It can even evoke aggression in people when they observe that kind of behavior.
Chapter 4: How can cortisol and serotonin levels affect aggressive behavior?
Many of you have probably heard the statement that I believe arises from pop psychology, not from formal academic psychology, that aggression is just sadness. It's a form of sadness that's amplified and it shows up as aggression.
Chapter 5: What tools can help reduce cortisol and manage aggression?
But when we look at the underlying biology and the peer reviewed literature on this, Nothing could be further from the truth. We have distinct circuits in the brain for aggression versus grief and mourning. Those are non-overlapping. Now that doesn't mean that you can't be sad and aggressive or in a state of mourning and aggressive at the same time.
Chapter 6: How does genetics influence aggression and irritability?
But the idea that sadness and aggression are one in the same thing is simply not true. And by understanding that, or perhaps by understanding that irritability and aggression are not the same thing.
Chapter 7: What is the impact of acetyl-L-carnitine on aggressive behavior?
You'll be in a much better position to apply some of the tools that we will talk about in this episode in order to be able to reduce or eliminate, or if it's adaptive to you to modulate aggression. And yes, there are cases where modulating your aggression in some cases, even amplifying aggression can be adaptive. One of the names that's most associated with the formal study of aggression
is none other than Conrad Lorenz. Conrad Lorenz studied so-called imprinting behaviors and fixed action pattern behaviors, patterns of behavior that could be evoked by a single stimulus.
The idea that you can get a whole category of behaviors, like looking to somebody for comfort and only them, the idea that you could get a huge category of different behaviors in a bunch of different contexts triggered by just the presence of that person.
is remarkable because what it suggested and what turns out to be true is that there are neural circuits, not just individual brain areas, but collections of brain areas that work together to engage a pattern of behaviors. And that's the first fundamental principle that we need to define today.
That when we talk about aggression, we're talking about activation of neural circuits, not individual brain areas, but neural circuits that get played out in sequence, like keys on a piano. but that playing out in sequence means that aggression is a verb. It has a beginning, a middle and an end, and it's a process. It's not an event.
And as you'll see, that turns out to be very important in terms of thinking about how one can halt aggression, prevent it from happening before it's initiated, or maybe even prolonging aggression if that's what's needed. Now, Conrad Lorenz had, no real knowledge of neural circuits. I mean, obviously he knew there was this thing that we call a brain and a nervous system.
And he knew that there were chemicals in the brain and hormones and things of that sort that were likely to play a role, but he really didn't take any measures to define what the neural circuits were. But he did think about what sorts of underlying processes could drive something like aggression. And he talked about one particular feature that's especially important.
And that's this notion of a pressure. The idea that yes, certain hormones will bias somebody or an animal to be aggressive. Certain neurotransmitter states, and you'll learn what those are today, will bias somebody to be more or less aggressive. And yes, of course, there will be historical features based on their childhood, et cetera, et cetera.
He understood that there will be a constellation of things that would drive people to be aggressive. And he described a so-called pressure, almost like a hydraulic pressure. Just think about fluid pressure in a small container being pushed, pushed, pushed until the can or the container is ready to explode.
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Chapter 8: What actionable strategies can help modulate aggression?
Now this effect of estrogen causing aggression in the brain is very robust, so much so that if you take a mouse that lacks the aromatase enzyme or a human that lacks the aromatase enzyme, and they do exist, then there is a reduction in overall aggression despite high levels of testosterone. It doesn't matter how much you increase testosterone or any of its other derivatives.
you do not observe this aggression. This runs counter to everything that we know and think about the role of testosterone. So the next time somebody says testosterone makes people aggressive, you can say, ah, no, actually it's estrogen that makes people aggressive and animals aggressive for that matter.
Now, of course, it is the case that because males have relatively less estrogen circulating in their brain and body than females, right, because they have testes, not ovaries, that testosterone is required in the first place in order to be converted into estrogen to activate this aggressive circuit involving these estrogen receptor containing neurons in the ventromedial hypothalamus.
So we've established that it's not testosterone, but testosterone converted into estrogen that activates these circuits for aggression. Nonetheless, it's still surprising, right? I mean, most of us don't think about estrogen as the hormone that stimulates aggression, but it turns out it's all contextual.
There are beautiful data showing that whether or not estrogen stimulates aggression can be powerfully modulated by whether or not days are short or days are long. In other words, whether or not there's a lot of sunshine or not.
Day length is converted into hormonal signals and chemical signals, and the primary hormonal and chemical signals involve melatonin and dopamine and also the stress hormones. So to make a very long story short, in the long days where we get a lot of sunlight, both in our eyes and on our skin. Melatonin levels are reduced.
Melatonin is a hormone that tends to produce states of sleepiness and quiescence. It also tends to activate pathways that tend to reduce things like breeding and sexual behavior. In long days, dopamine is increased. Dopamine is a molecule associated with feelings of wellbeing and motivation and the desire to seek out all sorts of things. And in long days,
provided we're getting enough sunlight on our skin and to our eyes, the stress hormones, especially cortisol and some of the other stress hormones are reduced in levels. If estrogen levels are increased experimentally under long day conditions, it does not evoke aggression. However, in short days, if estrogen is increased, there is a heightened predisposition for aggression.
And that makes perfect sense if you think about what short days do to the biology of your brain and body. The melatonin signal goes up. There's more melatonin circulating for more of each 24-hour cycle. Stress hormones are circulating more. Why? Short days tend to be associated with winter
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