Chapter 12 II - Attack and Escape Behaviors The startle...

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Attack and Escape Behaviors • The startle reflex is the extremely fast response to unexpected loud noises. – found in young infants and suggest fear is built-in and unlearned • Auditory information stimulates an area of the pons that commands the tensing of the neck and other muscles. – Information reaches the pons within 3 to 8 milliseconds after – The startle response occurs within two- tenths of a second.
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Attack and Escape Behaviors • Current mood or situation can modify the reaction • Startle reflex is more vigorous if already tense • Cells in the amygdala, especially the basal lateral and central nuclei, receive information from pain, vision, and hearing circuits. • Axons extend to areas in the midbrain that relay information to the nucleus in the pons. • The relay enhances the startle reflex.
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Attack and Escape Behaviors • Output from the amygdala to the hypothalamus controls autonomic fear responses. • Axons extending from the amygdala to the prefrontal cortex regulate approach and avoidance responses.
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Attack and Escape Behaviors • Damage to the amygdala interferes with: – the learning of fear responses – retention of fear responses previously learned – interpreting or understanding stimuli with emotional consequences
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Attack and Escape Behaviors • In the early 1900s, studies of monkeys with Kluver-Bucy syndrome illustrated the effects of amygdala damage. • Monkeys with this syndrome are calm and placid and display less than normal fear of snakes and larger, more dominant monkeys. • Also alters social behaviors in that they have decreased ability to interpret threat gestures. • Amygdala damage can also lead to an increase in the approach motive.
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Attack and Escape Behaviors • fMRI studies suggest the amygdala responds strongly to emotional stimuli and facial expressions. – Not necessarily associated with just fear. • Activity is strongest when the meaning is unclear and requires some processing. • Responds more strongly to an angry face averted away from the viewer and frightened faces directed towards the viewer. • Amygdala also responds to stimuli not consciously perceived.
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Attack and Escape Behaviors • In humans, damage to the amygdala does not result in the loss of emotion. • Damage to the amygdala impairs the
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Chapter 12 II - Attack and Escape Behaviors The startle...

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