Lec #18 emotion

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Neuroscience: Exploring the Brain, 3e

Chapter 18: Brain Mechanisms of Emotion


IntroductionIntroduction

• 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


What Is Emotion?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


What Is Emotion?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


The Limbic System ConceptThe Limbic System Concept• Broca’s Limbic Lobe

– Cortex forming a ring around corpus callosum: Cingulate gyrus, medial surface temporal lobe, hippocampus


The Limbic System ConceptThe 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


The Limbic System ConceptThe 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



• 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



• 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


The Amygdala and AssociatedBrain CircuitsThe Amygdala and AssociatedBrain Circuits• Anatomy of the

Amygdala


The Amygdala and AssociatedBrain CircuitsThe Amygdala and AssociatedBrain 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


The Amygdala and Associated Brain CircuitsThe Amygdala and Associated Brain Circuits

• Learned Fear

– Amygdala involved in forming memories of emotional events

– Confirmed by fMRI images and PET imaging


The Amygdala and AssociatedBrain CircuitsThe Amygdala and AssociatedBrain 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


The Amygdala and AssociatedBrain CircuitsThe Amygdala and AssociatedBrain 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


Neural Components of Aggression Beyond the AmygdalaNeural 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.



• The Hypothalamus and Aggression (Cont’d)

– Flynn, 1960s

• Elicited affective aggression by stimulation 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 grey; affective aggression


Serotonin and AggressionSerotonin 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


Serotonin and AggressionSerotonin and Aggression

• Serotonin Receptor Knockout Mice

– 14 serotonin receptor subtypes

– Knockout Mice (recombinant DNA techniques)

– 5-HT1A and 5-HT1B

– 5-HT1A and 5-HT1B autoreceptors—global regulatory role

– 5-HT1B High concentrations in raphe nuclei, amygdala, PAG, basal ganglia

– Agonists: Decrease anxiety, aggressiveness


Concluding RemarksConcluding 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


End of Presentation

Lec #18 emotion

Education

Transcript of Lec #18 emotion