W2L1 - Fear Conditioning and Extinction

Question 1

What is fear conditioning a form of and what does it involve?

Answer 1

• Associative Learning or Classical conditioning
  
  • Pairing aversive stimulus (US; Shock) with neutral stimulus (CS; Light)
  • Original neutral stimulus (CS; Light) leads to fear response (CR)

Question 2

What is classical and operant condiioning. Similarity/Differences

Answer 2

Classical:

• Associating automatic involuntary behaviour and stimulus
• Neutral stimulus before reflex

Operant:

• Associating voluntary behaviour and consequence
• Apply reinforcement or punishment to strengthen or weaken behaviour

Question 3

What is fear extinction?

Answer 3

Gradual reduction of fear response when the conditioned stimulus is repeatedly presented without aversive outcome

Question 4

What are three properties of fear extinction?

Answer 4

• Fear extinction requires extensive traning and fragile, unlike fear conditioning (rapid and robust)
  
  • Spontaneous Recovery: Time
  • Renewal: Context
  • Reinstatement: Re-exposed to original US
• Fear extinction is context-dependent
  
  • Learning to reduce fear in one context may not translate to another
• Fear extinction produces new memory trace (CS without aversive outcome), inhibiting original CS-US fear association
  
  • Not erase, but inhibit

Question 5

What are typical procedures in animal studies of fear conditioning/extinction

Answer 5

1. ) Conditiong acquisiton phase
   * Light/tone is paired with shock
2. ) Extinction phase (Different chamber for context)
   * Presented with repeated trials of light without shock
3. ) Test Phase
   * Subsequent day to assess retention of extinction

Question 6

From Rodent Studies, How is fear conditioned in the brain (Neurologically)?

Answer 6

1. Sensory input (CS) from auditory/visual cortex pairs with pain signals (US) from somatosensory cortex in basolateral nucleus of amygdala
2. Conditioned association from BLA activates central nucleus of amygdala
3. Central nucelus of amydala sends afferent to hypothalamic and midbrain regions controlling arousal, freezing, hormonal response.

Question 7

Difference between low and high road

Answer 7

Low Road:

• Autonmatic, rapid, reflexive fear response
• Senory input > thalamus > amygdala

High Road:

• Slower cortical inhibitory response.

Question 8

What are the key areas in fear in RODENTS

Answer 8

Prelimbic Cortex (PL)

• Stimulation increase fear and inactivation reduces fear
• Activity predicts poor extinction
  
  • dACC equivalent
  • Fear conditioning

Infralimbic Cortex (IL)

• Stimulation reduces fear and inactivation impairs extinction
• Activity predicts good extinction
  
  • vmPFC equivalent
  • Fear extinction

Question 9

What does human neuroimaging found in regions for fear conditioning and extinction

Answer 9

Conditioning

• dACC
  
  • Threat appraisal
• Bilateral anterior insula
  
  • Introspective awareness of fear

Extinction

• vmPFC

Question 10

What are 3 explanations as to a lack of amygdala activity in human fear conditioning studies?

Answer 10

• Resolution of fMRI
  
  • Can’t image subnucleii of amygdala
• Amygdala only recruited with intense threat as part of defence-circuitry response (mild anxiety in human studies)
• Amygdala response habitutate after repeated trials

Question 11

According to meta-analysis of fear extinction studies, what is the difference between humans and rodents neurologically

Answer 11

Compared to rodents, humans have

• Less robust vmPFC activation
• More robust dACC and anterior insula (similar to fear conditioning)

Question 12

Why are there similar activation in fear conditioning and extinction

Answer 12

1. dACC and anterior insula involved in threat appraisal and experience of anxiety, but they perform different functions
2. Networks might be activated but no behavioural experience of conditioning (dissociation in fear measures)
3. Role of vmPFC in extinction is debated, could be contextual processing

Question 13

Why are three explanations fear conditioning and extinction involved in etiology of anxiety disorders

Answer 13

• Greater conditionability of CS + of anxetiy disorders
• Greater stimulus generalization
  
  • Greater Reactivity to CS+ and Generalization to CS-
• Impaired capacity to inhibt fear to CS+

Question 14

When compared healthy and anxious participants, what were the results

Answer 14

• Greater conditionability of CS + of anxetiy disorders
  
  • No Difference
• Greater stimulus generalization
  
  • Greater Reactivity to CS+ and Generalization to CS-
  • Overgeneralization in anxious patients
• Impaired capacity to inhibt fear to CS+
  
  • Reduced Capacity

Question 15

What are results of fear extinction and PTSD

Answer 15

Compared to Trauma-exposed controls,

• No greater conditionability in PTSD
• Evidence of impaired fear extinction in PTSD
  
  • Increased amygdala activitng during extinction recall
  • Reduced vmPFC activity during extinction recall

Question 16

What is the link between PTSD symptoms and extinction

Answer 16

• Long-term PTSD have impaired extinction post-trauma (and pre-trauma)
• Deficits in extinction networks (reduced vmPFC) and increase amygdala activity to threat is normalized after exposure therapy for PTSD (i.e. increase vmPFC; decrease amygdala activity)