Chapter 11 - Emotion

11.1. Emotions, Aggression, and Stress

Emotions

• Definition of Emotions

  • Subjective Mental State: Emotions involve personal feelings that vary greatly from individual to individual.
  • Cognition: Emotions require conscious evaluation of experiences, meaning they involve a thought component.
  • Physiological Responses: Emotions trigger involuntary physical sensations through activation of the autonomic nervous system, specifically the sympathetic and parasympathetic systems.
  • Behavioral Responses: Emotions promote observable actions such as defending, attacking, or laughing.

• Emotions as Motivational Programs

  • Emotions have evolved as adaptive programs to coordinate responses to various situations. For example:
  • Fear programs improve survival by enabling responses to dangerous situations.
  • Disgust responses, which are often elicited by visual signals (such as another individual's disgust), are aimed at preventing infection by avoiding contaminated substances.

Psychological Theories of Emotion

• Folk Psychology: Suggests that feelings trigger autonomic reactions (e.g., the view that getting scared results in increased heart rate).
• James-Lange Theory: Proposes that emotions arise from autonomic reactions; we feel an emotion because we have these physical reactions.
  • Critique: Autonomic reactions are not exclusive to emotions.
• Cannon-Bard Theory: Argues that emotions and autonomic reactions occur simultaneously and independently.
• Schachter-Singer Theory (Two-factor Theory): Suggests that emotions are derived from physiological arousal and cognitive interpretation of that arousal.
  • This implies that how we label our emotions is context-dependent.
• Constructed Emotion Theory by Barrett: Proposes that emotions are actively constructed through various cognitive processes, including attention and interoception (the sense of internal body states), with the experience formed by contextual factors rather than being hardwired in specific brain areas.

Core Set of Emotions

• Although there is no universal agreement on the number of basic emotions, Paul Ekman and Robert Plutchik proposed theories about their classification:
  • Plutchik identified eight core emotions categorized into pairs of opposites:
    • Happiness/Sadness
    • Affection/Disgust
    • Anger/Fear
    • Expectation/Surprise
  • Other researchers suggest emotions like contempt and embarrassment may also be part of the core emotional spectrum.

Facial Expressions and Their Role

• Common Ancestry in Expressions: Similarities in facial expressions between humans and nonhuman primates suggest a shared evolutionary ancestor.
• Mechanisms Mediating Facial Expressions:
  • Muscles involved in facial expressions fall into two categories:
  • Superficial Facial Muscles: Attach to skin, allowing for finer, expressive movements.
  • Deep Facial Muscles: Connect to bone, responsible for larger movements such as opening the mouth.
  • Innervation: Two cranial nerves involved — the Facial nerve (VII) and the Motor branch of the Trigeminal nerve (V).

Duchenne and Non-Duchenne Smiles

• A Duchenne smile is characterized by genuine emotion, involving both the mouth and eyes, activated by the limbic system.
• A non-Duchenne smile is considered a social gesture, primarily using the mouth and controlled by the motor cortex, such as a forced smile.

Role of Facial Expressions in Communication

• Facial expressions serve vital roles in overt communication, often involuntary and linked to emotions like contempt.
• Microexpressions: Brief flashes of expression that reveal true feelings but can be easily overridden by conscious control.
• The brain contextualizes these expressions, showing that a smile may not always reflect happiness, and contextual factors help interpret emotional signals.

Facial Feedback Hypothesis

• This hypothesis indicates that sensory feedback from facial expressions can influence the emotional experience, as supported by evidence that people adopting certain expressions (e.g., smiling) report intensified feelings of those emotions.
• Research shows that Botox can diminish the expression of emotions due to paralysis of facial muscles, leading to reduced emotional intensity.

The Evolution of Emotional Processing in the Brain

• Historically, emotion was viewed as localized primarily within the limbic system (especially Papez circuit), but modern understanding reflects a more distributed neural processing approach.
• Studies highlight that the amygdala is critical for fear processing, with inputs from the medial amygdala concerning pheromones and odors determining aggression and fear responses.

Fear Conditioning Models

• Animal models demonstrate that classical conditioning can evoke fear behaviors (like freezing) and physiological changes (e.g., increased blood pressure) through association with aversive stimuli (e.g., shock).

Key Neural Mechanisms in Emotion

• The Medial Forebrain Bundle (MFB) and the Amygdala play crucial roles in emotions, especially in fear response:
  • MFB conveys dopamine-related teaching signals, impacting motivational states and feelings of elation.
  • The amygdala serves as a conditioning center for fear, shaped by high-level cognitive processes.

Dual-Pathway Model of Fear

• Proposed by Joseph LeDoux:
  • Low Road: Rapid pathway for fear; bypasses the cortex, directing stimuli straight to the amygdala (immediate reactions).
  • High Road: Slower cognitive analysis path, traveling to the cortex for evaluation (contextual understanding).

Neuroscientific Insights into Fear

• Recent studies suggest the amygdala's role in fear is complex and not solely a \"fear center\", as emotions are finally conceptualized as whole-brain processing events involving multiple networks and regions.

Aggression and Stress

Aggression

• Definition: Aggression is behavior intended to harm others, both physically and emotionally, particularly prominent among males (e.g., men are arrested for murder five times more than women).
• Influential Factors:
  • Testosterone: Elevated levels correlate with increased aggression in various species, evidenced by studies showing castration reduces aggression levels in male mice.
    • Human studies yield mixed results, indicating that testosterone might merely correlate with aggressive behavior rather than causing it.
  • Serotonin: Inversely correlated with aggression; lower serotonin levels are associated with increased aggression and violent behavior.
• Ventromedial Hypothalamus (VMH): Crucial for aggressive behavior mediation, receiving information about odors and pheromones, with stimulation leading to aggressive responses.

Stress

• Definition: Physiological response to aversive or threatening stimuli, triggered by the release of hormones from adrenal glands, specifically cortisol and catecholamines (Epinephrine and Norepinephrine).
• HPA Axis Activation:
  • Hypothalamic-Pituitary-Adrenal (HPA) axis controls cortisol release from the adrenal cortex, interacting with glucocorticoid receptors significantly influencing stress levels.
  • Sympathetic nervous system activation leads directly to rapid release of Epi and NE further enhances the stress response known as the \"fight or flight\" reaction.
• Individual Differences in Stress Responses: Vary due to genetics and prior experiences.
  • Studies show that early experiences with stress can shape later responses—for example, rat pups exposed to mild stress exhibit resilience, but require comforting afterward to mitigate extreme stress responses.

Chronic Stress Effects

• Chronic exposure to stressors has been shown to suppress immune functions and overall health, diverging from the short-term physiological benefits intended for survival in immediate danger.
• Implications: Long-term stress can lead to significant health deterioration and increased vulnerability in individuals.

Summary of Key Factors

• Aggression

  • Increased Testosterone levels (in animals)
  • Decreased Serotonin levels
  • Involvement of the Ventromedial Hypothalamus

• Stress

  • Stress Responses mediated by adrenal hormones
  • Activation of the HPA Axis (Cortisol)
  • Role of the Sympathetic Nervous System (Epinephrine and Norepinephrine)
  • Variations in Responsivity: Sensitization vs. Resilience
  • Effects of Chronic Stress on health.