Neurobiology of Fear

Question 1

define fear

Answer 1

Adaptive state of apprehension with rapid onset followed by rapid dissipation once threat is removed

Question 2

Patient SM

Answer 2

• has no amygdala (no fear center) due to Urbach-Wiethe disease
• Other emotions are similar to typical people, but reduced fear
• However, stimulus matters:
• • Environment (ex. Snakes, spiders, scary movies): no fear
• • Threat to life/homeostasis (ex. excessive CO2): fear-like responses

Question 3

amygdala

Answer 3

• located near bottom of hippocampus

- controls emotional learning & memory, fear, and reward

Question 4

path to fear

Answer 4

• First response (stimulus -> thalamus)
• Amygdala activated -> induces arousal, adrenaline, heart rate, and blood pressure
• Amygdala also stimulates PVN to increase cortisol in circulation (amygdala -> hypothalamus -> cortisol)

Question 5

path to reason

Answer 5

• Higher reasoning (thalamus -> sensory cortex -> frontal cortex)
• Careful appraisal by sensory and frontal cortices dampen the amygdala’s reaction (frontal cortex sends reduced signals to amygdala)
• Logic prevails, fear is removed and cortisol levels return to normal

Question 6

path to anxiety (misguided fear)

Answer 6

• Same path as reason, but frontal cortex sends increased signals to amygdala, producing fear
• Left unchecked, chronic elevations in cortisol result in a variety of disorders (increased cortisol stimulates amygdala, increasing cortisol, and so on)

Question 7

animal learning from single-stimulus experience

Answer 7

• Arbitrary cue: blue stick
• Rat pays more attention to the new object: sensitization
• Over time, rat takes less notice of the object: habituation

Question 8

classical conditioning

Answer 8

• pairing a stimulus with another stimulus to elicit a response (Ex. Pairing blue stick with cat odor to elicit fear when they see blue stick)
• could be an adaptive form of learning that helps an organism survive by changing its behaviour to better suit its environment
• can condition baby animals too (Ex. Rat pups can be conditioned to prefer certain neutral odors if they’re paired with a reward (ie. Brush stroking))

Question 9

conditioned stimulus vs. unconditioned stimulus

Answer 9

• Conditioned stimulus: stimulus that fails to elicit a response, but will once it’s paired with second (unconditioned) stimulus
• Unconditioned stimulus: stimulus that elicits response without training

Question 10

appetitive stimulus vs. aversive stimulus

Answer 10

• Appetitive stimulus: stimuli that are considered pleasant or rewarding (eg. Food)
• Aversive stimulus: unpleasant stimuli (ex. Cat odor)

Question 11

classical FEAR conditioning

Answer 11

• Ex. Pairing sound with slight shock -> tone will eventually elicit fear response
• Can condition baby animals too (Ex. Pairing scent with slight shock in baby rats)
• Can’t happen to organisms without amygdalae

Question 12

how is fear conditioning unique for baby animals?

Answer 12

• very young rat babies (ex. 8-day-old rat pups) actually still prefer odor associated with shock initially, then once they get older (ie. 12+ days) they show aversion to it
• why:
• • altricial infants (must attach to caregiver to survive)
• • Amygdala is not activated at day 8 (this is likely critical in not forming a conditioned fear response to parents, but it is activated by the time you’re ready to move outside of the nest)

Question 13

altricial infants

Answer 13

• survival depends on attachment to caregiver; infant brain wired to form attachments
• Newborns need to form attachment to caregiver to increase its chances of survival; independent of caregiver quality (ex. Abusive caregiver); evolution favours attachment

Question 14

influence of maternal presence on baby animals’ amygdalas

Answer 14

• Maternal presence can modulate fear-conditioning during a transitional sensitive period by altering amygdala activity -> mother acts as switch between the two learning systems
• Ie. 10-16 day period: if mom is present, they don’t form aversion; if mom is not present, they do form aversion
• When mom is there, amygdala is quieted; when mom isn’t there, amygdala is activated

Question 15

Alex Honnold

Answer 15

• solo free-climber whose amygdala is not activated when he sees scary things
• could have differences in reward circuitry (needs more stimulate to release dopamine), creating a “super-sensation-seeker”
• could have trained himself to be fearless
• could be on one extreme of genetic variability in fear responses

Question 16

sensation-seekers

Answer 16

• Genetic component
• Lower anxiety
• Blunted response to danger – resulting in a tendency to underestimate risk
• low amygdala activity