Pavlovian Conditioning,
Fear Circuits and Extinction of Fear
Valance Wang
Translational 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
US
¬CS
CS
P( US | CS ) = 0.4
CS
US
¬CS
P( US | CS ) = P( US | ¬CS) = P(US) = 0.4
CS
P( US | ¬CS ) = 0.4
US
¬CS
Contingency in Pavlovian Conditioning
US
¬CS
CS
P( US | CS ) = 0.4
CS
US
¬CS
P( US | CS ) = P( US | ¬CS) = P(US) = 0.4
CS
P( US | ¬CS ) = 0.4
US
¬CS
Is this associative learning?
Causal Attribution in Pavlovian Conditioning
Blocking
N
→
Unblocking
L
N
Shock
N
Shock
L
Shock
L
N
L
Shoc
k!
?
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!