Two groups of mice (control and experimental) received contextual fear conditioning as shown in the figure below. As shown, both groups were then subjected to a memory test 24 hours after training. The control group showed the expected ‘freezing’ response represented by the blue bar on the graph below.

Which of the following conditions may have the experimental group been subjected to in order to observe the results shown by the red bar during the memory test?

Question

Two groups of mice (control and experimental) received contextual fear conditioning as shown in the figure below. As shown, both groups were then subjected to a memory test 24 hours after training. The control group showed the expected ‘freezing’ response represented by the blue bar on the graph below.

Which of the following conditions may have the experimental group been subjected to in order to observe the results shown by the red bar during the memory test?

BlackTom AI · Accepted Answer

Engram neurons are the cellular substrate of a specific memory, and consolidation of a newly formed memory requires protein synthesis soon after training. Both ideas are central to interpreting freezing behavior in contextual fear conditioning: strong freezing at test indicates successful encoding and recall; reduced freezing indicates either failure to consolidate the memory or disruption of the specific neurons that store/express it.

1) Relevant knowledge points and concepts
- Engram neurons: cells activated during learning that store the memory; their integrity is required for later recall.
- Memory consolidation: conversion of a labile memory into a long-term form requires protein synthesis; inhibitors like anisomycin block consolidation and produce amnesia when given immediately after training.
- Behavioral readout: freezing during the context test is a measure of recall; reduction in freezing means impaired memory/consolidation or disrupted recall mechanisms.

2) Step-by-step reasoning
- Observation: experimental group (red bar) shows much less freezing than control (blue bar) at 24 h. This implies the experimental manipulation impaired the memory or its retrieval.
- Which manipulations can cause this?
  - Ablating engram neurons prior to recall removes the neuronal substrate needed for expressing the memory; therefore freezing will be reduced or absent.
  - Administering anisomycin immediately after training prevents protein synthesis required for consolidation; the memory fails to stabilize and is not recalled 24 h later, producing reduced freezing.
- Which manipulations would not produce reduced freezing?
  - Ablating non-engram neurons should not disrupt the specific memory trace, so freezing would be preserved.
  - Activating engram neurons prior to the test would evoke the memory (and likely increase freezing), not decrease it.

3) Intermediate logical steps
- If manipulation disrupts engram integrity or consolidation → no recall → low freezing.
- Ablation of non-engram cells or activation of engram cells → either no effect or enhanced recall → not consistent with low freezing.

4) Why the correct answer is correct
Both option A (ablation of engram neurons before recall) and option D (anisomycin immediately after training) would produce the observed low freezing by either removing the memory trace or preventing its consolidation.

5) Why other options are incorrect
- B: Ablating non-engram neurons should not selectively abolish the learned freezing response.
- C: Activating engram neurons should elicit or enhance freezing, not reduce it.

6) Conclusion
Therefore the manipulation that fits the observed reduced freezing is either A or D; the correct choice is e) A or D.

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