Emotion, Agression, and Stress

Emotion

subjective mental state (i.e., a feeling)

Autonomic nervous system

PNS and SNS

Sympathetic nervous system

“fight or flight” system; prepares the body for action

Parasympathetic nervous system

prepares the body for rest and recuperation 

Folk psychology (“common sense”):

External stimuli produce an emotional response, which triggers autonomic responses in the body.

James-Lange Theory

External stimuli produce an autonomic reaction, which triggers an emotional response.

Cannon-Bard Theory

The brain must interpret the situation to decide which emotion is appropriate.

Schachter and Singer Theory

Cognitive appraisal of the context attributes an emotion to an autonomic response.

Neural Circuit for Facial Expressions

Commands from the face area in the motor cortex control the cranial nerve, specifically the facial nerve (Cranial nerve VII), which innervates superficial muscles; these muscles attach between points of facial skin to enable expressions.

Facial Feedback Hypothesis

Suggests that facial expressions can influence emotional experiences, supporting the James-Lange theory of emotion.

Nonhuman Expressions of Emotion

Evidence includes chimpanzees showing a play face, homologous to the human laugh, and mice displaying emotional-like expressions in response to sensory stimuli assumed to trigger emotions.

Biological Function of Emotions

Emotions provide motivational 'programs' that are evolutionarily advantageous for survival (e.g., fear, disgust).

Types of Emotion Models

Discrete models and dimensional models are used for classifying emotions. A main weakness of discrete models is that they may not account for the complexity of emotional experiences.

Universality of Emotional Facial Expressions

Research shows that emotional facial expressions can be affected by cultural conditioning.

Circumplex Model

A prominent dimensional model of emotion that classifies emotions along two dimensions: arousal and valence.

Brain Self-Stimulation

Involves brain regions such as the septum and medial forebrain bundle that project to the nucleus accumbens, which is part of the reward circuit.

Decorticate Rage

Refers to a reaction implicating subcortical generation but cortical inhibition of rage.

Limbic System

The limbic system is central for emotion processing and includes important regions such as the thalamus, cingulate cortex, hippocampus, and amygdala.

Limbic Circuit for Emotion Processing (Fear)

1. Sensory organ detects external stimulus and sends information to the thalamus.

   2. Low road: thalamus projects directly to amygdala, producing a quick, subconscious fear response.

   3. High road: thalamus projects to sensory cortex/hippocampus, which then projects to amygdala, producing a slower, conscious fear response.

Amygdala

Coordinates behavioral, autonomic, and hormonal responses to fear.

Emotional Learning and the Amygdala

Evidence suggests the amygdala plays a crucial role in emotional learning, which can be studied using classic fear conditioning experiments that pair a neutral stimulus with an aversive event to elicit a fear response.

Klüver-Bucy Syndrome

Results from amygdala damage that leads to loss of emotional learning, causing behavioral effects such as increased placidity, loss of fear response, and inappropriate social behaviors.

Complex Emotions and Brain Mapping

Complex emotions have spatially distributed correlates in the brain, indicating a lack of one-to-one mapping between specific emotions and singular brain regions.

Neural Pathways for Facial Expressions

fMRI and electrophysiological recordings in macaques suggest that the neural pathways for emotion-driven and voluntary facial expressions are intermingled, indicating overlap in the mechanisms governing both types of expressions.

Aggression

A behavior intended to cause pain or harm to others, with types including:

1. Intermale aggression – aggression between males of the same species

2. Lethal aggression – aggression capable of killing

3. Maternal aggression – aggression of females in defense of their nest or offspring.

Evolutionary Advantage of Lethal Aggression

Evidence suggests that lethal aggression amongst male chimpanzees serves an evolutionarily advantageous function by increasing access to resources and females.

Testosterone and Aggressive Behavior

In nonhumans, there is a clear positive relationship between testosterone levels and aggressive behavior. In humans, the relationship is less straightforward and confounded by factors like the vicarious testosterone response, showing altered testosterone levels may result from aggressive behavior rather than being the cause.

Serotonin and Aggression

Researchers infer serotonin concentrations by studying levels of its metabolite (5-HIAA) in cerebrospinal fluid. Evidence indicates that higher levels of serotonin inhibit aggression in both humans and nonhumans.

Cortisol and the Dual-Hormone Hypothesis

The dual-hormone hypothesis suggests that cortisol levels interact with testosterone levels to regulate aggressive (or empathic) behavior, with low cortisol and high testosterone associated with increased aggression.

Twin Studies on Aggressive Behavior

Twin studies allow researchers to examine the heritability of aggressive behavior, providing evidence that genetic factors play a significant role.

MAOA Activity and Aggressive Behavior

Low MAOA activity leads to altered serotonin release, and evidence suggests that low MAOA, in interaction with childhood maltreatment, impacts aggressive behavior.

Neural Circuit for Aggression in Rodents

The medial amygdala differentiates the sex of other mice, while neurons in the ventromedial hypothalamus (VMH) serve as a 'switch' for turning on/off aggressive behavior.

Personality Traits of Psychopathy

Psychopathy is characterized by a constellation of personality traits such as superficial charm, high intelligence, lack of empathy, guilt or remorse, manipulativeness, and antisocial behavior.

Cortical Thinning and Violent Behavior

Evidence suggests that psychopathy and other forms of extremely violent behavior may result from cortical thinning of the temporal lobe, including many limbic structures that are crucial for moral decision-making.

Neural Characteristics of Psychopathy

Psychopathy exists along a spectrum, contrasting individuals classified as psychopaths at one end with extreme altruists at the other. This spectrum reflects varying degrees of emotional response and moral reasoning.

Limbic Pathways and Stress Response

Upon encountering a stressful stimulus, the limbic pathways (the 'low road' and 'high road') send information to the amygdala, which in turn sends neural distress signals to the hypothalamus.

Hypothalamic Coordination of Stress Responses

The hypothalamus coordinates two types of stress responses:

1. HPA Axis Activation: Neuroendocrine cells in the paraventricular nucleus secrete releasing hormones that prompt the anterior pituitary to release adrenocorticotropic hormone (ACTH) into the bloodstream. ACTH binds to the adrenal cortex, triggering the secretion of cortisol, which readies the body for action.

   • Cortisol suppresses the immune system and redirects energy towards metabolic processes.

   • Glucocorticoid receptors in the hypothalamus help regulate cortisol levels via negative feedback.

Activation of the Sympathetic Nervous System

The hypothalamus activates autonomic preganglion neurons in the brainstem/spinal cord, which innervate the adrenal medulla (the core of the adrenal gland). This response results in the secretion of the hormones epinephrine and norepinephrine, preparing the body for 'fight or flight' on a faster timescale than the cortisol response: elevating heart rate, breathing, blood sugar, and muscle tension.

Stress Hormones Concentration Changes

Research illustrates the relative changes in concentration of the three stress hormones (cortisol, epinephrine, norepinephrine) and testosterone levels surrounding stressful events.

Nurturing Behavior and Stress Response

Nurturing behavior during infancy impacts adults' responses to stressful events. Individuals with nurturing experiences in childhood tend to exhibit better stress management skills in adulthood.

Brain Basis of Individual Differences in Stress Response

Reduced hippocampal neurogenesis in adults who were neglected/abused during youth, results in decreased stress control. Epigenetic regulation alters gene expression, resulting in a reduced number of glucocorticoid receptors in adults who experienced early neglect/abuse, making cortisol less effective at dampening stress.

Psychoneuroimmunology

Evidence from psychoneuroimmunology shows that psychological and emotional factors (such as stress or happiness) influence immune system functioning.

Chronic Stressors and Health Outcomes

Chronic stressors produce adverse health outcomes from an evolutionary perspective, as the stress response evolved for dealing with acute stressors (brief, immediate threats) and prolonged exposure to the stress response can lead to negative health effects.