A patient with a dog phobia completes successful exposure therapy and shows no fear response to dogs. Six months later, after a period of high stress, their fear of dogs returns strongly. Which explanation best fits the neuroscience of extinction?
AThe exposure therapy failed to create a true extinction memory, so the original fear was never reduced
BStress hormones chemically erased the extinction memory, allowing the original fear trace in the BLA to re-emerge
CExtinction created a competing inhibitory memory that suppressed the original fear trace; stress weakened this inhibitory memory without erasing the original association
DThe patient formed a new CS-US association between stress and dogs during the intervening period
Extinction does not erase the original CS-US association encoded in the basolateral amygdala — that trace is essentially permanent. What extinction creates is a new inhibitory memory (encoded in prefrontal cortex-amygdala circuits) that competes with and suppresses the original fear. This inhibitory memory is fragile and context-sensitive. Stress impairs prefrontal control of the amygdala, weakening the suppressive trace and allowing the original fear memory to dominate — a phenomenon called reinstatement. Options A and D misunderstand the extinction mechanism; B incorrectly implies chemical erasure of the extinction memory rather than functional suppression of the inhibitory circuit.
Question 2 Multiple Choice
You hear a loud bang and flinch before you consciously recognize what the sound was. Which feature of amygdala circuitry best explains this?
AThe central amygdala sends direct projections to sensory cortex to speed conscious perception
BThe basolateral amygdala receives direct projections from the thalamus that bypass cortical processing, enabling rapid threat responses before full perceptual analysis
CThe hippocampus rapidly retrieves contextual memories of past danger, triggering a preemptive fear response
DThe prefrontal cortex accelerates sensory processing during threatening situations to reduce reaction time
The basolateral amygdala receives two types of sensory input: a slow, detailed cortical route and a fast, crude thalamic route that bypasses the cortex entirely. This 'low road' allows the amygdala to initiate a defensive response before full sensory analysis is complete — which is why you flinch at a snake-shaped stick before your visual cortex finishes determining it's just a stick. This evolutionary design favors speed over accuracy: false alarms are far less costly than missed threats.
Question 3 True / False
Extinction therapy permanently erases the conditioned fear memory stored in the basolateral amygdala.
TTrue
FFalse
Answer: False
This is the most clinically important misconception about fear extinction. The original CS-US association in the BLA persists essentially intact after successful extinction. What changes is not the original memory but the presence of a new, competing inhibitory memory. The evidence: fear spontaneously recovers after a delay, returns when the person is back in the original conditioning context (renewal), and reinstates after stress. All three phenomena are explained by the inhibitory memory being fragile and context-dependent while the original fear trace is robust — which also explains why therapy focused purely on extinction often shows high relapse rates.
Question 4 True / False
Amygdala-dependent fear associations can be formed in a single CS-US pairing.
TTrue
FFalse
Answer: True
One-trial fear learning is a feature, not a bug. The basolateral amygdala supports rapid acquisition of threat associations through long-term potentiation at CS-US synapses — sometimes requiring only a single pairing, especially when the unconditioned stimulus is intense. This rapid acquisition makes evolutionary sense: an organism that needs dozens of exposures to learn a lethal predator is a dead organism. This also explains why traumatic memories are often encoded with exceptional vividness and durability from a single exposure.
Question 5 Short Answer
Why does 'just knowing you're safe' often fail to eliminate fear responses, and what does this imply about the relationship between the original fear memory and extinction?
Think about your answer, then reveal below.
Model answer: Knowing you're safe is a cortical, conscious-level representation. The original fear memory encoded in the basolateral amygdala operates below conscious control and was not overwritten by extinction — only suppressed by an inhibitory memory dependent on prefrontal-amygdala circuits. Intellectual knowledge (cortical) and conditioned fear (subcortical) are separate systems. Extinction creates a competing inhibitory trace, but this trace is context-specific and can be overwhelmed by stress, re-exposure to the original context, or the passage of time — all of which disengage prefrontal suppression and allow the original BLA trace to drive behavior.
This dissociation between knowing and fearing is one of the most important clinical insights from fear neuroscience. It explains why cognitive reassurance alone is often insufficient for phobia and PTSD treatment, and why effective therapies must work at the level of the inhibitory memory — building it through repeated exposures across multiple contexts, consolidating it through sleep, and protecting it with emotional regulation strategies that maintain prefrontal control.