Pavlovian Conditioning, Fear Circuits and Extinction of Fear Valance Wang Translational...
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Transcript of Pavlovian Conditioning, Fear Circuits and Extinction of Fear Valance Wang Translational...
Pavlovian Conditioning, Fear Circuits and Extinction of Fear
Valance WangTranslational Neuromodeling & Computational Neuroeconomics
Fall 2013
Overview
Pavlovian conditioning
Definition and variations
Fear conditioning and fear circuits in the brain
Amygdala in human and animals
Extinction of fear
Pavlovian conditioning (or classical conditioning):
Unconditional Stimulus → Unconditional Response
Conditioning: ( CS → US )→ UR
US is biologically relevant:
reward (food, water) and punishment (noise, electric shock)
air-puff to the eye
Variations of Pavlovian Conditioning
Second-order conditioning
CS1 → (CS2 → US)
Preconditioning
(CS1 → CS2) → US
Contingency in Pavlovian Conditioning
P( US | CS ) = 0.4
P( US | CS ) = P( US | ¬CS) = P(US) = 0.4
P( US | ¬CS ) = 0.4
¬CS CSUS
¬CSCS US
¬CSCS US
Contingency in Pavlovian Conditioning
P( US | CS ) = 0.4
P( US | CS ) = P( US | ¬CS) = P(US) = 0.4
P( US | ¬CS ) = 0.4
¬CS CSUS
¬CSCS US
¬CSCS US
Is this associative learning?
Blocking
→
Unblocking
Causal Attribution in Pavlovian Conditioning
N
Shock
L N
Shock
L
N
Shock
L N
Shock!
L
Relative validity of X
?
Relative validity of X
Relation to drug addiction
Fear Conditioning
Fear conditioning
Fear conditioning works across phyla:
snails, worms, flies
fish, pigeons, rabbits, rats, cats, dogs and humans
Human Amygdala
In humans
Patients with amygdala damage shows deficits in perception of emotional meaning of the faces, esp. fearful faces, and emotional tone of voices.
fMRI studies show that amygdala is activated more strongly in presence of fearful and angry faces than of happy faces.
Fear conditioning leads to increased amygdala activity.
Fear Circuits in the Brain
Sensory inputs mainly terminate in LA:
auditory thalamus
auditory cortex
fear conditioning to a simple auditory CS can be mediated by either pathway
damage to LA interferes with fear conditioning
Thalamo-amygdala pathway:
single unit recordings show cortical pathway learns more slowly over trials than the thalamic pathway
fMRI show that human amygdala’s activity changes during conditioning correlates with the thalamus but not the cortex
Contextual conditioning:
After conditioning, rats exhibited fear when returning back to the experiment chamber
Contextual conditioning is mediated via hippocampus
Ventral hippocampus projects to B and AB
Damage to these areas interferes with contextual conditioning
Output pathway: CE projects to
brainstem
lateral hypothalamus → blood pressure
peraqueductal grey → freezing
bed nucleus of stria terminalis → pituitary-adrenal stress hormone
Role of amygdala in fear memory:
Inactivation of amygdala during training prevents fear conditioning;
Inactivation of amygdala immediately after conditioning blocks memory formation.
In humans, damage to amygdala interferes with implicit emotional memory, but not explicit memories about emotions (which is controlled by medial temporal lobe).
Extinction of Fear
Extinction training: repeated presentation of CS without US
Extinction training has not been successful, because the fear may return, for example with stress.
A recent study in human attempts to extinct the fear by targeting at memory reconsolidation window.
During reconsolidation, stored memory is rendered labile after being retrieved. Pharmacological manipulation in the reconsolidation window results in inability to retrieve the memory at later times.
Extinction training conducted during the reconsolidation window successfully block the return of fear response.
The effect remains after 1 year.
The extinction effect is CS-specific.
References
Bouton (2006): Chapter 3: The nuts and bolts of conditioning.
LeDoux (2000): Emotion circuits in the brain.
Schiller et al. (2010): Preventing the return of fear in humans using reconsolidation update mechanisms.
THank you!