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

Huberman starts with a basic question: how do emotions differ from states, and why might it be more useful to think in terms of states? Anderson answers that emotions are a subset of internal states. Arousal, motivation and sleep belong to the same class. What these states share is that they "change the input-to-output transformation of the brain." His example is sleep: a sleeping person doesn't hear a sound they would hear if they were awake.

Anderson says the state framing "puts the focus on it as a neurobiological process rather than as a psychological process." He separates emotion from feeling, which many people treat as the same thing. Feeling is a subjective experience. It can only be studied in humans, because the only way to learn what someone feels is to ask them, and people are the only animals that can talk in a way we can understand. That gives the state approach its practical advantage: it lets researchers study the parts of emotion that can be observed in animals.

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.

Anderson notes that some researchers have described emotion with just two dimensions, arousal and valence. He and Ralph Adolphs have tried to extend that list to other components. They focus especially on the features that separate emotion states from motivational states, which he calls "very closely related."

The first feature is persistence, which sets state-driven behavior apart from simple reflexes. A reflex, like the knee jerk when a doctor taps with a hammer, starts when the stimulus starts and stops when it stops. By contrast, "Emotions tend to outlast, often, the stimulus that evoke them." His example is hearing a rattlesnake on a Southern California trail. You jump, your heart keeps pounding and your palms keep sweating after the snake has gone. You also stay hypervigilant, so you stop at a stick that only remotely looks like a snake.

Anderson qualifies this: "Not all states have persistence." Hunger ends once you have eaten. Anger can last long after the fight that triggered it, and it takes a while to calm down.

The second feature is generalization: a state triggered in one situation can carry over into another. In his example, a parent comes home to a screaming child. After a good day at work, they might pick the child up and soothe it. After a bad day, they might react very differently.

Components of emotion states Anderson describes: arousal and valence (the traditional two dimensions); persistence (outlasting the stimulus, unlike reflexes, though not all states have it); generalization (carrying a state from one situation into another).

Huberman asks about aggression and mentions the work of Dayu Lin and others in Anderson's lab. Anderson first clarifies the term. To him, aggression describes a behavior more than an internal state. The behavior could reflect a state we would call anger in humans, or fear, or hunger in the case of predatory aggression.

While she was in Anderson's lab, Lin found a way to evoke aggression in mice. She used optogenetics to activate specific neurons in the ventromedial hypothalamus (VMH). This followed the Nobel Prize-winning work of Walter Hess, who evoked two kinds of aggression in cats depending on where in the hypothalamus he placed his electrode. One was defensive rage: ears back, teeth bared, hissing. The other was predatory aggression: ears forward, batting with a paw at a mouse-like object as if to catch and eat it.