Chapter 18: Brain Mechanisms of Emotion Neuroscience: Exploring the Brain, 4e Chapter 18: Brain Mechanisms of Emotion

Introduction Affective neuroscience Emotional experience, emotional expression Behaviors presumed the expressions of internal emotions. Brain mechanisms of emotion derived from: Animal models Human studies Brain lesions No one emotion system like sensory systems

Early Theories of Emotion The James–Lange theory: emotion experienced in response to physiological changes in body The Cannon–Bard theory: emotions occur independent of emotional expression—no correlation with physiological state

Implications of Unconscious Emotion Stimulus can have emotional impact without conscious awareness. Aversive conditioning to masked stimulus results in increased skin conductance Increased activity in the amygdala Many possible ways for the brain to process emotional information Different emotions may depend on different neural circuits.

Unconscious Emotional Brain Activity

The Limbic System Broca’s limbic lobe Areas of brain forming a ring around corpus callosum: cingulate gyrus, medial surface temporal lobe, hippocampus

The Papez Circuit Limbic structures, including cortex, involved in emotion Emotional system on the medial wall of the brain linking cortex with hypothalamus

The Papez Circuit—(cont.) Cortex critical for emotional experience Hippocampus governs behavioral expression of emotion Rabies infection implicates hippocampus in emotion -> hyperemotional responses Anterior thalamus Lesions lead to spontaneous laughing or crying. Paul MacLean popularized the term limbic system. Evolution of limbic system allows animals to experience and express emotions beyond stereotyped brain stem behaviors.

The Limbic System—(cont.) Difficulties with the single emotion system concept Diversity of emotions and brain activity Many structures involved in emotion No one-to-one relationship between structure and function Limbic system: use of single, discrete emotion system questionable

Emotion Theories and Neural Representations Early theories of emotion and limbic system built on introspection and inference from brain injury and disease. Studies of disease and consequences of lesions not ideal for revealing normal function. More recent theories of emotion Basic emotion theories Dimension emotion theories

Basic Emotion Theories Certain emotions thought unique, indivisible, universal experiences Hypothesis that basic emotions have distinct representations or circuits in brain Analogous to distinct representations for sensory experiences Anger, disgust, fear, happiness, sadness, surprise fMRI shows different activation with the basic emotions. Patterns of activity, not single areas, may represent emotions.

Dimension Emotion Theories Emotions can be broken down into smaller fundamental elements. Combined in different ways and differing amounts Emotions correspond to brain activation along dimensions such as valence and arousal. Psychological constructionist theories of emotion Variation on dimensional theories Includes nonemotional psychological components Emotion an emergent consequence of combined components

A Dimensional Representation of Basic Emotions

What Is an Emotion? Great diversity of perspectives on nature of emotions Unknown whether each emotion is represented by: Activity in a specialized area of the brain A network of areas A more diffuse network of neurons Study approaches Behavioral observations Physiological recordings Studies of effects of lesions and disease

Fear and the Amygdala Research on fear and anger provides good examples of study of emotion. The amygdala seems critical for emotion of fear. Other brain structures also involved Amygdala active also in other emotional states Much research has been done on the amygdala.

The Klüver–Bucy Syndrome Produced by temporal lobectomy in rhesus monkeys Decreased fear and aggression Decreased vocalizations and facial expressions of fear Temporal lobe lesions in humans—particularly lesions in amygdala Exhibit symptoms of Klüver–Bucy syndrome Flattened emotions

Anatomy of the Amygdala

Effects of Amygdala Stimulation and Lesions Bilateral amygdalectomy reduces fear and aggression in all animals tested. Anger, sadness, and disgust may also be affected. S.M. case study: inability to recognize fear in facial expressions Electrical stimulation of amygdala -> increased vigilance or attention—anxiety and fear in humans fMRI imaging: Fearful faces evoke greater amygdala activity than happy or neutral faces.

Learned Fear Amygdala involved in forming memories of emotional and painful events Confirmed by fMRI images and PET imaging

Anger and Aggression—Intertwined in Animals Predatory aggression—attack Against different species for food Few vocalizations, attack head or neck No activity in sympathetic division of ANS. Affective aggression—for show Used for show, not kill for food High levels of sympathetic activity Makes vocalizations, threatening posture Amygdala lesions in animals -> less aggression

The Amygdala and Aggression Surgery to reduce human aggression Amygdalectomy Psychosurgery—now treatment of last resort Results Reduced aggressive behavior Relief from anxiety Profound, unpleasant side effects

Neural Components of Anger and Aggression Beyond the Amygdala The hypothalamus and aggression Removal of cerebral hemispheres but not hypothalamus -> sham rage Behavior reversed with additional lesions in hypothalamus Hypothalamus may normally be inhibited by telencephalon.

The Hypothalamus and Aggression Flynn’s research Elicited affective aggression by stimulating medial hypothalamus Predatory aggression elicited by stimulating lateral hypothalamus

The Midbrain and Aggression Two hypothalamic pathways to brain stem involving autonomic function Medial forebrain bundle -> ventral tegmental area; predatory aggression Dorsal longitudinal fasciculus -> periaqueductal gray matter; affective aggression

A Neural Circuit for Anger and Aggression

Serotonergic Regulation of Anger and Aggression Serotonin deficiency hypothesis Aggression is inversely related to serotonergic activity. Serotonergic raphe neurons project to the hypothalamus and limbic structures via the medial forebrain bundle. Serotonin turnover—aggression in rodents Drug PCPA blocks serotonin synthesis—aggression In humans also, reports of negative correlation between serotonin activity and aggression

Concluding Remarks Controversy remains about extent to which emotions cause body changes or bodily changes cause emotions. Brain imaging shows emotions are associated with widespread brain activation. Some brain structures activated in multiple emotional states, others more specific to particular emotions. Emotional experiences are the result of complex interactions among sensory stimuli, brain circuitry, past experiences, and activity of neurotransmitter systems.