Lec #18 emotion

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


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?
• 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 Concept
• Broca’s Limbic Lobe
– Cortex forming a ring around corpus callosum: Cingulate
gyrus, medial surface temporal lobe, hippocampus


• 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 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 Associated
Brain Circuits
• Anatomy of the
Amygdala


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

The Amygdala and Associated Brain Circuits
• Learned Fear
– Amygdala involved in forming memories of emotional
events
– Confirmed by fMRI images and PET imaging


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

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


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.


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


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


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


Serotonin 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 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

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