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

Emotions are considered a type of internal state, which are neurobiological processes that change the brain's input-to-output transformation and control behavior. This perspective shifts focus from subjective feelings to underlying neural mechanisms.

Internal states can be characterized by persistence (how long they outlast the stimulus), intensity (how strong they are), and generalization (how they apply across different situations). They also have a valence (positive or negative).

Arousal is not unitary; there are behavior-specific forms of arousal, such as sexual arousal versus aggressive arousal. Research in fruit flies suggests different neural circuits mediate distinct arousal states, even if they share common neurochemicals like dopamine.

Aggression is multifaceted and involves different circuits depending on its type. For example, offensive aggression (often rewarding) is linked to the ventromedial hypothalamus (VMH), while defensive aggression (fear-driven) and predatory aggression involve other distinct circuits.

In regions like the VMH, fear and offensive aggression neurons are intermingled. This proximity might facilitate the hierarchical dominance of fear over offensive aggression, allowing fear to shut down aggressive behaviors, as fear neurons can inhibit aggression neurons.

While testosterone is involved in male aggression, its effects are often mediated by its conversion to estrogen via aromatization. Estrogen and progesterone, classically considered female reproductive hormones, play a significant role in controlling aggression in male mice.

Female mice primarily exhibit aggression when nurturing pups, becoming hyper-aggressive during maternity. This involves a neural switch in the VMH, where aggression-promoting neurons become highly active, overriding mating circuits, a mechanism not observed in males.

Yes, mounting behavior in male mice can be either sexual or a dominance display. Sexual mounting is accompanied by ultrasonic vocalizations and activates the medial preoptic area (MPOA), while dominance mounting lacks vocalizations and activates the ventromedial hypothalamus (VMH).

The PAG acts like a 'telephone switchboard,' implicated in various innate behaviors including pain modulation, fear responses (panic, freezing), and lordosis. Different sectors of the PAG receive projections from hypothalamic regions and are involved in routing information to determine specific behavioral outputs.

Tachykinins are neuropeptides whose levels increase significantly in the brain during social isolation in flies and mice. This upregulation drives increased aggressiveness, fear, and anxiety, and blocking tachykinin receptors can reverse these effects without sedation.