Emotions 2
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Emotions 2






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Emotions 2 Emotions 2 Presentation Transcript

  • Emotion Expression & Experience
  • What is emotion?
    • No scientific definition
    • Controlled by distinct neuronal circuits within the brain
    • We experience emotion consciously
      • therefore there is a cognitive element, most likely involving the cerebral cortex
    • Emotion can be viewed as an outcome of the interaction of peripheral & central factors
  • Responses to Emotion
    • Emotion is accompanied by autonomic, endocrine & skeletomotor responses
    • Thus it also depends on sub-cortical parts, including:
      • amygdala
      • hypothalamus
      • brain stem
  • Peripheral Responses
    • Peripheral responses prepare the body for action
    • Communicate emotions to other people
    • Example – fear:
      • increased heart rate & respiration
      • dry mouth
      • tense muscles
      • sweaty palms
  • The Autonomic Nervous System & Emotion
    • Most changes that accompany emotional states are mediated by autonomic nervous system
    • The autonomic system is primarily an effector system
      • controls smooth muscles, heart, exocrine glands
      • autonomic is involuntary
  • Three Divisions of the ANS
    • Sympathetic
      • governs fight or flight response
      • response to stress
    • Parasympathetic
      • rest and digest
      • Normal conditions
    • Enteric
  • Role of the Hypothalamus
    • Contains many of the neuronal circuits that regulate functions that vary with emotion:
      • Temperature
      • heart rate
      • blood pressure
      • water and food intake
    • also controls pituitary gland & thereby the endocrine system
    • controls output of autonomic nervous system
  • Hypothalamic Control of the ANS
    • The hypothalamus acts on ANS in 2 ways:
    • Projects to 3 important regions in the brain stem & spinal cord:
      • to the nucleus of the solitary tract
      • receives sensory input from viscera
      • to the brain stem in the rostral ventral medulla
      • leads to general sympathetic activation
      • directly to the autonomic outflow of the spinal cord
    • The hypothalamus acts on endocrine system to release hormones that influence autonomic function
  • Experimental Evidence
    • Emotional states are elicited by stimulating the hypothalamus
    • Stephen Ranson - 1932
      • stimulated different regions of the hypothalamus in anesthetized animals
      • Evoked autonomic reactions including changes of heart rate, blood pressure, etc.
    • Walter Hess - 1940’s
      • used awake animals
      • produced behaviors and physiologic changes characteristic of particular emotions e.g. fear
  • Cortical Centers of Emotion
    • Physiological inputs to the hypothalamus act on the brain stem & autonomic nervous system.
    • This information reaches the cerebral cortex from the peripheral organs.
    • This gives rise to the conscious perception of emotion
    • So where is the cortical representation of emotion?
  • The Limbic System Concept
    • Is there a “system” ( a group of structures that function together) responsible for emotion?
    • Scientists identified the limbic system as the key pathway in emotion – 1930’s
      • Paul Broca
      • James Papez
  • Broca’s Limbic Lobe
    • Paul Broca – 1878
    • Identified a portion of cortex present in all mammals which is different from surrounding cortical tissue
      • These areas form a ring or border around the brainstem
      • Limbus = border , thus limbic lobe
    • Includes:
      • cortex around the corpus callosum, especially in the cingulate gyrus
      • Cortex on the medial surface of the temporal lobe, including the hippocampus
    • Broca did not relate these structures to emotion
  • The Papez Circuit
    • James Papez- 1930’s
    • Proposed that there is an emotion system that links the cortex to the hypothalamus
      • Emotion is determined by the activity of the cingualte cortex
      • Emotional expression is governed by the hypothalamus
    • The Papez Circuit
      • A group of structures, each connected to the next by a major fiber tract
      • The cingulate cortex projects to the hippocampus, which projects to the hypothalamus through the fornix; the hypothalamus projects to the anterior nuclei of the thalamus, which reach back to the cortex
  • Papez Circuit
  • Studying Emotion
    • Emotional expression
      • behavioral manifestations of internal emotion
    • Emotional experience
      • subjective feelings of emotion
    • Limitations of animal models
      • can study emotional expression but cannot investigate emotional experience
    • Limitations of human experiments
      • very often the medical situation which provides information involves damage to or compromise of other neural structures and functions in an uncontrolled way
  • Theories of Emotion- James & Lange
    • William James & Karl Lange - 1884
    • Proposed that the experience we call emotion occurs after the cortex receives signals about physiologic changes
      • Emotional expression precedes emotional experience
      • Physiological changes occur in response to stimuli, then we feel emotions
    • Emotion is the consequence of information from the periphery
      • We feel sorry because we cry
    • The physiological changes are the emotion
  • Critique of James & Lange
    • Emotions are experienced even if physiological changes aren’t sensed
      • Patients & animals with transected spinal cords do not have lessened emotions
    • The same physiological changes accompany different emotions and can have other causes
      • e.g. fear, anger & disease can all increase heart rate & cause sweating
  • Theories of Emotion – Cannon & Bard
    • Walter Cannon and Phillip Bard - 1927
    • Stimuli cause emotional experience
    • Emotional experience can occur independently of emotional expression
    • The thalamus plays a pivotal role in emotional sensations
    • Emotions are produced when signals reach the thalamus directly from sensory receptors or by descending cortical input
    • The emotion is determined by the pattern of activation of the thalamus
  • The Somatic Marker Hypothesis
    • Stanley Schacter:
    • The cortex constructs emotion out of signals received from the periphery
    • This is called the somatic marker hypothesis:
    • Emotion is a story the brain concocts to explain bodily reactions
      • Depends expectations, experience, social context
      • Thus the same responses can accompany different emotions
  • Current Theories
    • Antonio Damasio -
    • Expanded somatic marker hypothesis
    • Draws a close connection between emotion and cognition.
    • Emotions are biologically indispensable to decisions.
    • Studied patients with damage to the amygdala or prefrontal cortex
      • Research on patients with frontal lobe damage indicates that feelings normally accompany response options
      • Operate as a biasing device to dictate choice.
    • “ Descartes error” – separating mind & body
  • The Current View
    • No single neural system produces emotions
    • Different emotions may depend on different neural circuits, but many of these circuits converge in the same parts of the brain
    • The limbic system may be involved in some emotional experiences, but it is not the sole neural system underlying emotion
    • Feelings (emotion) result from the interplay between:
      • The amygdala, hypothalamus, brain stem & autonomic nervous system and . . .
      • between amygdala and frontal & limbic cortex
  • Fear & Anxiety
    • The amygdala is the critical structure
    • Also involves the hypothalamus & ANS
    • Demonstrated by:
    • Kluver-Bucy Syndrome
    • Electrical stimulation experiments
    • Patients with damage to the amygdala
  • Klüver-Bucy Syndrome
    • Heinrich Kluver & Paul Bucy - 1939
      • bilateral removal of the temporal lobes in monkeys (which contains the amygdala & hippocampal formation) 
    • Radical changes in emotional behavior
      • increased and bizarre sexual behavior
      • highly oral
      • failed to recognize familiar objects ( psychic blindness)
        • temporal lobe destruction of visual cortices
      • emotionally flat
        • absence of fear - amygdala missing
  • Kluver-Bucy Syndrome
  • The Amygdala
    • Structure critical to emotional part of Kluver-Bucy syndrome is the amygdala
    • The amygdala is part of the limbic system
    • Human patients with damaged amygdalas have reduced ability to recognize fear in others
    • Electrical stimulation leads to fear and anxiety
    • A learned fear response, where pain is associated with a sensory input, may involve a circuit through the basolateral nuclei & central nucleus of the amygdala
    • These effects are mediated through the hypothalamus & autonomic nervous system.
  • The Amygdala
  • Anger and Aggression
    • Definitions:
    • Predatory aggression
      • leads to an attack for food
      • motive is to kill other animal
    • Affective aggression
      • behavior for show to scare other animal
      • lots of sympathetic ANS activity
    • Mediated by the hypothalamus, midbrain & amygdala
    • May also involve serotonin
  • The Role of the Hypothalamus
    • When the entire cerebral hemispheres are removed, sham rage results
      • Small stimuli provoke violent responses
      • Difficult to interpret because the entire neocortex is missing
      • Removal of anterior hypothalamus, sham rage still occurs
      • Removal of the posterior hypothalamus, sham rage vanishes
      • Conclusion: posterior hypothalamus is important for aggression and is normally inhibited by neocortex
    • Electrical stimulation of the hypothalamus
      • Stimulation of medial hypothalamus leads to affective aggression - hiss and spit at mouse
      • Stimulation of lateral hypothalamus leads to predatory aggression
  • Possible Role of the Midbrain
    • Major outputs of hypothalamus to brain stem are
    • Medial forebrain bundle (mfb)
      • project to ventral tegmental area
      • Electrical stimulation of ventral tegmental area can cause predatory aggression
      • Lesions in ventral tegmental area can abolish affective aggression
    • Dorsal longitudinal fasciculus (dlf)
      • project to periaqueductal gray matter
      • Electrical stimulation of PAG can elicit affective aggression and lesions can abolish affective aggression
  • Possible Role of the Amygdala
    • Ablation experiments indicate that the amygdala is also involved in aggression
      • amygdalectomy reduces aggression
    • Two pathways for aggression:
    • Predatory aggression - cortex > amygdala > lateral hypothalamus > mfb > ventral tegmental area
    • Affective aggression - cortex > amygdala > medial hypothalamus > dlf > periaqueductal gray matter
    • Led to psychosurgical procedures to destroy amygdala in humans
      • Frontal lobotomy is another example of psychosurgery
  • Possible Role of Serotonin
    • Experimental evidence suggests that blocking or reducing the synthesis or release of serotonin may increase aggressive behavior
    • When the gene for serotonin receptors are removed in mice, they become more aggressive
    • The type of receptor that is most effective when deleted is normally found in the amygdala, periaqueductal gray matter, and basal ganglia, as well as the raphe nuclei
  • Summary
    • No single neural system produces emotions
    • Brain structures involved in emotion are multi functional
      • there are interesting relationships among emotion, memory, and olfaction
    • Emotion results from the interplay between:
      • The amygdala, hypothalamus, brain stem & autonomic nervous system and . . .
      • between amygdala and frontal & limbic cortex