The formation of fear memory (or "fear conditioning’’) involves long-term potentiation (LTP) of synaptic connections in the region of the brain called the amygdala. The result is that the inputs conveying neutral stimuli (such as the environmental context) are able to elicit the fear response (such as the response to an aversive stimulus like a electric shock to the foot). After fear conditioning:

Question

BlackTom AI · Accepted Answer

Long-term potentiation (LTP) in the amygdala strengthens synapses so that previously neutral sensory inputs (the conditioned stimulus, e.g., an auditory cue) can drive fear responses. Thus, after conditioning, auditory stimuli become more effective at activating amygdala neurons.

1) Relevant knowledge points and concepts
- Classical (Pavlovian) fear conditioning pairs an unconditioned aversive stimulus (US, e.g., foot-shock) with a neutral conditioned stimulus (CS, e.g., tone or environmental context).
- The lateral and basolateral amygdala are key loci where CS–US associations form. LTP at synapses conveying the CS increases synaptic efficacy.
- Enhanced synaptic efficacy means that presentation of the CS now elicits action potentials in amygdala output neurons, producing conditioned fear responses (freezing, autonomic changes).
- Autonomic branches: fear and nociceptive stimuli primarily engage the sympathetic nervous system (fight-or-flight), not parasympathetic activation.

2) Step-by-step reasoning
- Before conditioning: auditory CS elicits weak or no amygdala firing; foot-shock US directly drives amygdala and unconditioned fear responses.
- During conditioning: repeated CS–US pairing induces LTP at synapses transmitting the CS into the amygdala.
- After conditioning: because those CS-related synapses are potentiated, the auditory CS produces much larger postsynaptic responses in amygdala neurons and so reliably triggers conditioned fear behaviors.

3) Calculations/intermediate steps
- Not applicable (no numerical calculation). The logical chain above shows synaptic strengthening → increased postsynaptic response → conditioned activation of amygdala.

4) Why the correct answer is correct
- The direct consequence of LTP in the amygdala is that previously neutral auditory stimuli become effective drivers of amygdala neuron firing and thus elicit fear. Electrophysiological recordings and lesion studies support that conditioned CSs activate amygdala neurons after learning.

5) Why the other options are incorrect
- "Foot-shocks can directly activate autonomic parasympathetic pathways": incorrect — aversive stimuli predominantly activate sympathetic, not parasympathetic, pathways.
- "Auditory stimuli are able to directly activate autonomic parasympathetic pathways": incorrect — conditioned auditory cues drive central fear circuits and sympathetic responses, not directly parasympathetic activation.
- "Foot-shocks elicit stronger fear behaviours": foot-shocks are the US and already elicit unconditioned fear; the key change after conditioning is that the CS now evokes fear via potentiated amygdala responses, not that the US becomes stronger.

6) Conclusion
The correct answer is: Auditory stimuli are more effective at activating amygdala neurons. This matches the provided answer.

类似问题

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What role do AMPA receptors play at synapses that exhibit NMDA mediated long-term potentiation? AMPA 受体在表现出 NMDA 介导的长时程增强作用的突触中发挥什么作用？

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