Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Neuroscience: Exploring the Brain, 3e Chapter 18: Brain Mechanisms of Emotion

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Introduction Significance of Emotions –Emotional experience; Emotional expression –Study behavioral manifestations Animal models, brain lesions –Human brain imaging techniques Renaissance in the study of emotion Affective neuroscience Neural basis of emotion and mood

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins What Is Emotion? Theories of Emotion –The James-Lange Theory: Emotion = Response to physiological changes in the body –The Cannon-Bard Theory: Emotions independent of emotional expression

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins What Is Emotion? Unconscious Emotions –Stimulus can have emotional impact without conscious awareness Aversive conditioning to masked stimulus results in increased skin conductance Increased activity in the amygdala –Many ways to process emotional information

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Limbic System Concept Broca’s Limbic Lobe –Cortex forming a ring around corpus callosum: Cingulate gyrus, medial surface temporal lobe, hippocampus

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Limbic System Concept The Papez Circuit –Limbic structures, including cortex, are involved in emotion. –Emotional system on the medial wall of the brain linking cortex with hypothalamus

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Limbic System Concept The Papez Circuit –Cortex: Emotional experience –Hippocampus: Hypothesized to mediate behavioral expression of emotion Rabies infection: Hyperemotional responses -cytological changes in hippocampal neurons - Anterior thalamus Lesions lead to spontaneous laughing, crying –Paul MacLean popularized term “limbic system” Evolution of limbic system allows animals to experience and express emotions beyond stereotyped brain stem behaviors

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Limbic System Concept Difficulties with the Single Emotion System Concept –Diverse emotions –Many structures involved in emotion No one-to-one relationship between structure and function –Limbic system: Utility of single, discrete emotion system questionable

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Limbic System Concept The Klüver-Bucy Syndrome –Temporal lobectomy in rhesus monkeys Decreased fear and aggression Decreased vocalizations and facial expressions –Temporal lobectomy in humans Exhibit symptoms of Klüver-Bucy syndrome Flattened emotions –Probably related to destruction of the amygdala

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Amygdala and Associated Brain Circuits Anatomy of the Amygdala

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Amygdala and Associated Brain Circuits The Amygdala and Fear –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 –Fearful faces produce greater amygdala activity than happy/neutral faces

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Amygdala and Associated Brain Circuits Learned Fear –Amygdala involved in forming memories of emotional events –Confirmed by fMRI images and PET imaging

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Amygdala and Associated Brain Circuits The Amygdala and Aggression –Predatory Aggression—Attacks 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

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins The Amygdala and Associated Brain Circuits The Amygdala and Aggression (Cont’d) –Surgery to Reduce Human Aggression Amygdalactomy Psychosurgery – last resort –Symptoms Reduced aggressive asocial behavior Increased ability to concentrate Decreased hyperactivity

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Neural Components of Aggression Beyond the Amygdala The Hypothalamus and Aggression –Removal of cerebral hemispheres but not hypothalamus -> sham rage –Behavior reversed with small lesions in hypothalamus –Hypothalamus may normally be inhibited by telencephalon.

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Neural Components of Aggression Beyond the Amygdala The Hypothalamus and Aggression (Cont’d) –Flynn, 1960s Elicited affective aggression by stimulation medial hypothalamus Predatory aggression elicited by stimulating lateral hypothalamus

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Neural Components of Aggression Beyond the Amygdala 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 grey; affective aggression

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Serotonin and Aggression Neurotransmitter Serotonin –Serotonergic raphe neurons project to the hypothalamus and limbic structures via the medial forebrain bundle –Serotonin turn-over aggression in rodents –Drug PCPA blocks serotonin synthesis aggression

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Serotonin and Aggression Serotonin Receptor Knockout Mice –14 serotonin receptor subtypes –Knockout Mice (recombinant DNA techniques) –5-HT 1A and 5-HT 1B –5-HT 1A and 5-HT 1B autoreceptors—global regulatory role –5-HT 1B High concentrations in raphe nuclei, amygdala, PAG, basal ganglia –Agonists: Decrease anxiety, aggressiveness

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Concluding Remarks Neural Pathways –Experience, expression of emotion involves widespread activity in the nervous system from cortex to ANS as well as: limbic structures, hypothalamus, amygdala –Structures involved in emotions have other functions, including learning and memory

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins End of Presentation