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

2. 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

3. 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

4. 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.

5. Unconscious Emotional Brain Activity

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

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

8. 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.

9. 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

10. 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

11. 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.

12. 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

13. A Dimensional Representation of Basic Emotions

14. 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

15. 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.

16. 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

17. Anatomy of the Amygdala

18. 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.

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

20. 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

21. 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

22. 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.

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

24. 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

25. A Neural Circuit for Anger and Aggression

26. 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

27. 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.