September 12, 2022 • 1hr 52min

Dr. David Anderson: The Biology of Aggression, Mating, & Arousal

Huberman Lab

Dr. David Anderson is a Professor of Biology at Caltech and a leading expert on the neurobiology of emotion, aggression, and social behaviors. In this wide-ranging discussion, Dr. Anderson explains his view of emotions as internal brain states that drive behavior, rather than purely subjective feelings. He describes key properties of emotional states like persistence and generalization, and how these are implemented in neural circuits. The conversation covers Dr. Anderson's groundbreaking work on aggression circuits in the mouse brain, the complex relationship between aggression and mating behaviors, and how social isolation increases aggression via neuropeptide signaling. Dr. Anderson also discusses the challenges of translating findings from animal research to human psychiatric treatments.

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Key Takeaways

Emotions are a type of internal state that changes how the brain processes inputs and generates outputs. Other internal states include arousal, motivation, and sleep.
States have several key properties including persistence (outlasting the initial trigger), intensity, generalization (applying to new situations), and valence (positive or negative).
Aggression involves multiple neural circuits controlling different types like offensive, defensive, and predatory aggression. The ventromedial hypothalamus (VMH) contains neurons that can trigger offensive aggression when stimulated.
Mating and aggression circuits are closely intertwined in brain regions like the VMH and medial preoptic area (MPOA). This allows integration of these behaviors but can also lead to confusion between aggressive and sexual motivations.
Social isolation increases aggression by upregulating neuropeptides called tachykinins in both flies and mice. Drugs blocking tachykinin receptors may have potential for treating isolation-induced aggression and anxiety in humans.
Emotions involve bidirectional communication between brain and body via the autonomic nervous system and vagus nerve. This underlies the subjective feeling of emotions in different body regions.

Introduction

Dr. David Anderson is a Professor of Biology at Caltech and a leading expert on the neurobiology of emotion, aggression, and social behaviors. In this wide-ranging discussion, Dr. Anderson explains his view of emotions as internal brain states that drive behavior, rather than purely subjective feelings. He describes key properties of emotional states like persistence and generalization, and how these are implemented in neural circuits.

The conversation covers Dr. Anderson's groundbreaking work on aggression circuits in the mouse brain, the complex relationship between aggression and mating behaviors, and how social isolation increases aggression via neuropeptide signaling. Dr. Anderson also discusses the challenges of translating findings from animal research to human psychiatric treatments.

Topics Discussed

Emotions vs. States (8:10)

Dr. Anderson explains his view of emotions as a type of internal brain state, rather than purely subjective feelings:

Emotions are one class of internal states, along with arousal, motivation, sleep etc.
States change how the brain processes inputs and generates outputs
Viewing emotions as states allows studying them as neurobiological processes in animals
Subjective feelings are just the "tip of the iceberg" of emotional states

"If you think of an iceberg, it's the part of the iceberg that's below the surface of the water. The feeling part is the tip that's sort of floating above the surface of your consciousness."

Dimensions of States: Persistence, Intensity & Generalization (10:36)

Key properties of emotional states include:

Persistence - states outlast the initial trigger
Intensity - states can vary in strength
Generalization - states can apply to new situations
Valence - states can be positive or negative

Dr. Anderson gives examples of how these properties distinguish emotional states from simple reflexes or motivational states.

Aggression, Optogenetics & Stimulating Aggression in Mice (18:11)

Dr. Anderson describes his lab's pioneering work on aggression circuits in mice:

Used optogenetics to stimulate neurons in ventromedial hypothalamus (VMH)
Activating VMH neurons triggers offensive aggression in male mice
This aggression is rewarding - mice will work to self-stimulate these neurons
Different from defensive or predatory aggression, which involve other circuits

"If we activate those neurons and the mouse has a chance to be in one of two compartments in a box, they will gravitate towards the compartment where those neurons are activated. It has a positive valence."

Aggression Types: Offensive, Defensive & Predatory (24:42)

Dr. Anderson explains different types of aggression and their neural bases:

Offensive aggression - triggered by VMH, rewarding for male mice
Defensive aggression - triggered by fear, involves different circuits
Predatory aggression - hunting behavior, uses separate pathways

These types of aggression involve different neural circuits and can be distinguished behaviorally in some species.

Hydraulic Pressures for States & Homeostasis (35:38)

Dr. Anderson discusses the concept of "hydraulic pressure" building up for behaviors:

Some behaviors like feeding have clear homeostatic pressure
Aggression doesn't seem to build up in the same way
But stimulating aggression neurons can lower the threshold for fighting
This may reflect increased neural activity in certain circuits

Aggression & Hormones: Estrogen, Progesterone & Testosterone (48:31)

Contrary to popular belief, estrogen and progesterone play key roles in male aggression:

Aggression neurons in male mice express estrogen receptors
Estrogen can restore aggression in castrated male mice
Progesterone receptors also involved in male aggression circuits
Testosterone's effects on aggression often mediated by conversion to estrogen

"Here are two hormones that are classically thought of as female reproductive hormones...And yet they're playing a very important role in controlling aggression in male mice and presumably in male humans as well."

Female Aggression, Motherhood (52:33)

Dr. Anderson describes research on female aggression in mice:

Female mice become highly aggressive when nursing pups
Separate populations of estrogen receptor neurons control mating vs fighting
Motherhood increases activity of aggression neurons relative to mating neurons
This flips the balance from mating to fighting behavior

Mating & Aggressive Behaviors (59:48)

The neural circuits for mating and aggression are closely intertwined:

VMH contains neurons activated during both mating and fighting
Medial preoptic area (MPOA) has "make love not war" neurons that inhibit aggression
Connections between VMH and MPOA help coordinate mating vs fighting
This close relationship may explain links between s*x and aggression

Mounting: Sexual Behavior or Dominance? (1:15:25)

Dr. Anderson explains how to distinguish sexual vs dominance mounting in male mice:

Male-male mounting often occurs in aggressive contexts
Sexual mounting accompanied by ultrasonic vocalizations
Dominance mounting occurs without vocalizations
Different brain regions activated during sexual vs dominance mounting

"You can easily distinguish whether mounting behavior by a male mouse is reproductive or agonistic aggressive, according to whether it's accompanied by ultrasonic vocalizations or not."

PAG (Periaqueductal Gray) Brain Region: Pain Modulation & Fear (1:24:40)

The periaqueductal gray (PAG) integrates multiple behaviors:

Involved in pain modulation, fear, aggression, and mating
May have topographic organization for different behaviors
Receives inputs from hypothalamic regions like VMH and MPOA
Helps coordinate autonomic and behavioral responses

Tachykinins & Social Isolation: Anxiety, Fear & Aggression (1:30:38)

Dr. Anderson describes his lab's work on neuropeptides called tachykinins:

Social isolation increases tachykinin levels in fly and mouse brains
Blocking tachykinin signaling prevents isolation-induced aggression
Drugs targeting tachykinin receptors may treat isolation effects in humans
But pharmaceutical companies reluctant to pursue due to past failures

"If you give those drugs to a socially isolated mouse, it blocks all of the effects of social isolation. It blocks the aggression, it blocks the increased fear and the increased anxiety."

Brain, Body & Emotions; Somatic Marker Hypothesis & Vagus Nerve (1:43:49)

Dr. Anderson discusses the relationship between brain, body and emotions:

Subjective feelings of emotion linked to bodily sensations
Autonomic nervous system mediates brain-body communication
Vagus nerve carries sensory and motor signals between brain and organs
New tools allowing study of specific vagal pathways in emotion

"This brain body connection is critical, not just for the gut, but for the heart, for the lungs, for all kinds of other parts of your body. And Darwin recognize that as well. And I think it's a central feature of emotion state, and I think what underlies our subjective feelings of an emotion."

Conclusion

This wide-ranging discussion with Dr. David Anderson provides a comprehensive overview of the neurobiology of emotions, aggression, and social behaviors. Key themes include viewing emotions as brain states rather than just feelings, the complex neural circuits underlying different types of aggression, and the close relationship between aggression and mating behaviors in the brain. Dr. Anderson's work highlights how basic research in animal models can provide insights into human emotions and psychiatric conditions. However, he also discusses the challenges in translating these findings to new treatments. Overall, this conversation demonstrates the power of modern neuroscience tools to dissect the biological basis of complex emotional and social behaviors.