The Neurobiology of Emotions

Emotions: Action-regulation systems that evaluate situations and coordinate adaptive responses, involving physiological regulation, action tendencies, and subjective feelings.
Feelings: The inner experiences of emotional states.
Mood: A sustained emotional state that continues after the initial stimulus is gone.
Temperament: Individual predispositions toward specific emotional states.
Affect: The outward display of an emotional state.
Phylogenesis of Capacity:
- Simple organisms (earthworms): Approach/avoidance reactions.
- Early vertebrates (fish, reptiles): Defensive and reward systems, brainstem, and hypothalamus.
- Mammals: Attachment and social emotions involving the limbic system (cingulate cortex, hippocampus).
- Primates: Hierarchy sensitivity and social learning.
- Humans: Symbolically and linguistically mediated emotions involving the default mode network and prefrontal cortex.

Cingulate gyrus: Responsible for attention allocation, motivation, and emotion regulation.
Amygdala: Detects emotional salience, threats, and relevance.
Nucleus accumbens: Manages reward motivation and reinforcement.
Hippocampus: Handles memory formation and spatial contextual processing.
Hypothalamus: Coordinates autonomic regulation.
Connective Structures:
- Fornix: Links the hippocampus with the hypothalamus.
- Stria terminalis: Links the amygdala to the hypothalamus and septal regions.
- Cingulum: Links the cingulate cortex to hippocampal regions.

Fear:
- The central nucleus of the amygdala triggers automatic fear reactions.
- The lateral nucleus facilitates learned fear and conditioned fear learning.
- Fear extinction involves inhibitory input from the ventromedial prefrontal cortex (vmPFC).
Anger and Aggression:
- Aggressive movements are programmed in the brain stem and controlled by the hypothalamus and amygdala.
- Serotonin (5-HIAA): Serotonergic activation inhibits aggressive/risky behavior. Low 5-HIAA is associated with assault and arson; high serotonin correlates with friendly behavior.
Disgust: Activated by the Insula and Basal Ganglia; functions primarily for disease prevention.
Laughter and Humor: The Anterior cingulate cortex produces muscular laughter. Humor appreciation requires the Right ventromedial PFC and the Nucleus accumbens.

Somatic Marker Hypothesis: Proposed by Damassio to show emotions are essential for social cognition.
Moral Dilemmas: The vmPFC is activated during moral consideration. Individuals with vmPFC lesions, such as those seen in cases by Damassio or the Phineas Gage case, make decisions based purely on utility.
Courage: Associated with the activation of specific sub-regions of the prefrontal cortex.

Expression Recognition: Darwin and Ekman argued facial expressions are innate and universal. Recognition is automatic and rapid, especially when posture is consistent with the expression.
Superior temporal sulcus (STS): Involved in monitoring gaze direction to adapt to social situations.
Motor Systems for Expression:
- Volitional facial paralysis: Damage to the face region of the primary motor cortex; patients cannot move muscles voluntarily but can make emotional expressions.
- Emotional facial paralysis: Damage to the insular prefrontal cortex or thalamus; patients can move muscles voluntarily but cannot produce emotional expressions.
Lateralization: The Right hemisphere plays a dominant role in emotional processes. Right lobe damage impairs the ability to identify emotional content in tone of voice. The left side of the face is typically more expressive and begins emotional expressions sooner.