Chapter 18 Brain Mechanisms of Emotion

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

The Limbic System Concept• Broca’s Limbic Lobe

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

What Is Emotion?• Unconscious Emotions

– Stimulus can have emotional impact without conscious awareness and increased activity in the amygdala

The Amygdala and AssociatedBrain Circuits

• Anatomy of the Amygdala

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

The Limbic System ConceptThe Limbic System Concept• The Papez Circuit

– Cortex: Emotional experience– Hippocampus: Behavioral expression of

emotion• Rabies infection:Implicates

hippocampus in emotion, -> Hyperemotional responses

– 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

Klüver-Bucy Syndrome

Displays similar symptoms in both Rhesus monkeys and in humans:

Overt sexual behavior increased dramatically (hypersexualism)

Monkeys & humans indulged in indiscriminate sexual behavior including significantly higher rates of masturbation and significant increases in both heterosexual and homosexual behavior

Emotionally, the monkeys & humans became dulled, and their facial expressions and vocalizations became far less expressive (loss of affect)

They were also less fearful of things that would have instinctively panicked them

This can be seen in severe cases of individuals with herpes, various forms of encephalitis, dementia like Alzheimer’s Disease and in many different forms of cerebrovascular disease.

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

• Flattened emotions– Probably related to

destruction of the amygdala

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

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