Engrams Studies (Lacagnina + Tse)
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Questions and Answers

What effect did silencing extinction-tagged neurons have during the initial light exposure?

  • Increased activity in neutral contexts
  • Increased freezing behavior (correct)
  • No significant effect
  • Reduced freezing behavior

    • What was the outcome of silencing fear acquisition-tagged neurons during a spontaneous recovery test 28 days later?

  • Reduced freezing behavior (correct)
  • Increased freezing behavior
  • No change in freezing behavior
  • Enhanced fear expression

    • What was the impact of stimulating fear acquisition neurons on fear expression?

  • No change in fear expression
  • Changed response in neutral contexts
  • Decreased fear expression
  • Increased fear expression (correct)

    • What conclusion can be drawn about extinction-tagged neurons based on the experiments?

    <p>They can suppress fear after activation</p> Signup and view all the answers

    What role do extinction-tagged neurons play according to the findings from the experiments?

    <p>Block spontaneous recovery of fear</p> Signup and view all the answers

    How did silencing extinction-tagged neurons affect behavior in a neutral context?

    <p>No effect</p> Signup and view all the answers

    What was demonstrated about the relationship between fear acquisition and extinction neurons?

    <p>They influence fear in opposing ways</p> Signup and view all the answers

    What was the effect of activating extinction neurons during extinction retrieval?

    <p>Reduced freezing behavior</p> Signup and view all the answers

    What effect does the stimulation of extinction neurons have on fear responses?

    <p>Decreased fear response</p> Signup and view all the answers

    Which statement about schemas is true?

    <p>Schemas improve understanding by providing frameworks.</p> Signup and view all the answers

    What does the data suggest about the role of the hippocampus in memory tasks?

    <p>It is crucial for learning flavor-place associations.</p> Signup and view all the answers

    Which type of memory is described as representing the position of objects relative to one another?

    <p>Allocentric memory</p> Signup and view all the answers

    How does systems consolidation occur according to the hypotheses presented?

    <p>Inherently involves the formation of schemas.</p> Signup and view all the answers

    What conclusion can be drawn from the results of the experiments on schema learning?

    <p>Schemas facilitated rapid memory encoding and consolidation.</p> Signup and view all the answers

    What effect does stimulation of contextual fear conditioning (CFC) neurons have?

    <p>Increased fear response during recall.</p> Signup and view all the answers

    What happens to memory performance when rats learn without an established schema?

    <p>Performance declines rapidly.</p> Signup and view all the answers

    What does spontaneous recovery refer to in the context of extinguished fear memories?

    <p>The reactivation of fear memories after a period of extinction</p> Signup and view all the answers

    Which region's projections to the amygdala play a crucial role in extinction memory acquisition?

    <p>Prefrontal cortex</p> Signup and view all the answers

    What type of activation does ChR2-eYFP allow in the context of optogenetics?

    <p>Excitation of neurons using blue light</p> Signup and view all the answers

    How are fear and extinction memories represented in the dentate gyrus according to the experiments?

    <p>They activate distinct, non-overlapping neuronal populations</p> Signup and view all the answers

    What was the purpose of using ArcCreERT2::Halo-eYFP in the experiments?

    <p>To label neurons active during extinction training</p> Signup and view all the answers

    What does the dentate gyrus (DG) contribute to in the study of fear memories?

    <p>Facilitating contextual fear memory formation</p> Signup and view all the answers

    During the extinction training, which type of neuronal activity was suppressed?

    <p>Fear acquisition neurons during fear retrieval</p> Signup and view all the answers

    Which component of the experimental design allows for permanent tagging of neurons?

    <p>Tamoxifen activating CreERT2</p> Signup and view all the answers

    What was the effect of lesions on the hippocampus 24 hours after training on new paired-associates?

    <p>Both lesioned and sham-lesioned animals effectively remembered original and new paired-associates.</p> Signup and view all the answers

    In Experiment 3, what was observed regarding rats with hippocampal lesions 48 hours post-training?

    <p>They could effectively recall new pairs, indicating memory transfer.</p> Signup and view all the answers

    What was the primary finding in Experiment 4 regarding the role of schemas in learning?

    <p>Mental schemas facilitate faster encoding and retention of new information.</p> Signup and view all the answers

    What conclusion can be drawn regarding rapid consolidation of new information?

    <p>It is faster within established schemas and is hippocampal dependent.</p> Signup and view all the answers

    How did rats' performance change when trained in consistent versus inconsistent schemas?

    <p>Performance improved in the consistent context, reflecting better learning.</p> Signup and view all the answers

    What happens to memory traces according to Experiment 3 findings?

    <p>They are transferred to the neocortex within 48 hours.</p> Signup and view all the answers

    What aspect of memory does a consolidated schema appear to resemble?

    <p>Semantic memory.</p> Signup and view all the answers

    What was reported about the timeline for consolidation in Experiment 2?

    <p>Consolidation occurs rapidly, usually in less than 48 hours.</p> Signup and view all the answers

    What was the effect of silencing extinction-tagged neurons on fear behavior during initial exposure to light?

    <p>Increased freezing behavior</p> Signup and view all the answers

    Silencing fear acquisition neurons has no effect on behavior during spontaneous recovery.

    <p>True</p> Signup and view all the answers

    What did stimulating fear acquisition neurons do to fear expression?

    <p>Increased fear expression</p> Signup and view all the answers

    Silencing extinction-tagged neurons is crucial only for __________ retrieval.

    <p>initial extinction</p> Signup and view all the answers

    Match the following neuronal activities with their outcome:

    <p>Silencing extinction-tagged neurons = Increased freezing behavior Silencing fear acquisition neurons = Reduced spontaneous recovery of fear Stimulating extinction-tagged neurons = Decreased freezing behavior Stimulating fear acquisition neurons = Increased fear expression</p> Signup and view all the answers

    What was concluded about the representation of fear acquisition and extinction in the hippocampus?

    <p>They are represented by distinct neuronal ensembles with opposing influences.</p> Signup and view all the answers

    Silencing fear acquisition neurons affects freezing behavior during the retrieval test.

    <p>False</p> Signup and view all the answers

    What persistent effects were observed when activating extinction neurons?

    <p>Blocked spontaneous recovery of fear</p> Signup and view all the answers

    Rapid consolidation of new paired-associates occurs within 48 hours if based on a previously learned schema.

    <p>True</p> Signup and view all the answers

    What was the primary factor that influenced the speed of learning in consistent versus inconsistent contexts?

    <p>The presence of a spatially based schema.</p> Signup and view all the answers

    The hippocampus is required for learning a __________ based schema of related food locations.

    <p>spatially</p> Signup and view all the answers

    What was a key result from Experiment 4 related to learning in a consistent schema?

    <p>New flavour-place associations were learned slower in inconsistent contexts.</p> Signup and view all the answers

    Both sham-lesioned and hippocampal-lesioned animals showed effective memory for original and new paired-associates.

    <p>True</p> Signup and view all the answers

    What role does sleep play in the consolidation of new memory traces according to Experiment 3?

    <p>Rapid consolidation requires a single sleep event.</p> Signup and view all the answers

    Match the following results with the appropriate experiments:

    <p>Experiment 1 = Hippocampus is required for learning spatial schemas. Experiment 2 = Rapid consolidation when learning is based on an established schema. Experiment 3 = Need for a single sleep event for rapid consolidation. Experiment 4 = Improvement in performance in consistent contexts.</p> Signup and view all the answers

    What effect does stimulation of extinction neurons have on fear response during spontaneous recovery?

    <p>Decreases fear response</p> Signup and view all the answers

    Schemas are built solely on new information and not on prior experiences.

    <p>False</p> Signup and view all the answers

    What are the two types of engrams mentioned in the context of fear responses?

    <p>CFC and Extinction</p> Signup and view all the answers

    The primary role of the hippocampus in memory tasks involves __________.

    <p>learning associations</p> Signup and view all the answers

    Match the following terms with their descriptions:

    <p>Allocentric memory = Spatial memory that represents positions relative to one another Schema = Frameworks of knowledge built from prior experiences Fear acquisition = Process of developing a fear response Fear extinction = Process of reducing a previously learned fear response</p> Signup and view all the answers

    How do schemas affect the process of memory encoding?

    <p>They enhance the ability to process new information</p> Signup and view all the answers

    Memory consolidation in the neocortex occurs quickly for all types of memories.

    <p>False</p> Signup and view all the answers

    What does spontaneous recovery refer to?

    <p>The relapse of fear after extinction training</p> Signup and view all the answers

    Extinction training completely erases the original fear memory.

    <p>False</p> Signup and view all the answers

    What role do prefrontal cortex projections to the amygdala play in extinction?

    <p>They are crucial for extinction memory acquisition.</p> Signup and view all the answers

    The ______ is essential for contextual fear memory.

    <p>dentate gyrus</p> Signup and view all the answers

    Match the following technologies with their uses in the study of fear memories:

    <p>ArcCreERT2::ChR2-eYFP = Activation of fear acquisition neurons ArcCreERT2::Halo-eYFP = Inhibition of extinction memories 4-OHT = Activation of recombinase Optogenetics = Control of neuronal activity with light</p> Signup and view all the answers

    Which of the following accurately describes the relationship between fear acquisition and extinction retrieval?

    <p>They are represented by distinct, non-overlapping DG neuronal ensembles.</p> Signup and view all the answers

    Fear memories and extinction memories are represented by distinct populations of DG neurons.

    <p>True</p> Signup and view all the answers

    What is the function of ChR2-eYFP in optogenetic experiments?

    <p>To excite or stimulate neuronal activity.</p> Signup and view all the answers

    Study Notes

    Distinct Hippocampal Engrams Control Extinction and Relapse of Fear Memory

    • Learned fear can relapse after extinction, highlighting that extinction forms a new memory coexisting with the original fear memory, rather than completely erasing it
    • Extinction does not permanently erase fear; fear can resurface over time (spontaneous recovery)
    • Extinction creates a new memory that suppresses or competes with the original fear memory
    • Projections from the prefrontal cortex to the amygdala are vital for acquiring extinction memory
    • Hippocampal activity is linked to extinction learning and its context-dependent retrieval
    • The dentate gyrus (DG) is crucial for contextual fear memory, with engram cells mediating fear expression
    • DG neurons involved in fear and extinction retrieval operate through distinct, non-overlapping neuronal assemblies.
    • Fear and extinction retrieval involve distinct, non-overlapping DG neuronal ensembles, despite similar overall DG activation.

    Design and Transgenics

    • Transgenic mice expressing either ArcCreERT2::ChR2-eYFP or ArcCreERT2::Halo-eYFP were used
    • Arc: promoter that creates tags
    • CreERT2: estrogen receptor bound by CRE (initially inactive)
    • 4-OHT (tamoxifen): activates recombinase, permanently tagging cells
    • eYFP: yellow fluorescent protein for tagging Arc
    • Methods using optogenetics:ChR2-eYFP (activating neurons with blue light) and Halo-eYFP (inhibiting neurons with green light) to target DG neurons
    • Activation occurs when CRE binds to Estrogen Receptor (ER) activating the recombinase
    • These mice were crossbred to express either ArcCreERT2::ChR2-eYFP or ArcCreERT2::Halo-eYFP.

    Procedure

    • Habituation
    • Fear conditioning training (associating context with fear stimulus)
    • Extinction training (exposing to context without the fear stimulus)
    • Conditional fear conditioning

    Results

    • Experiment 1: Extinction suppresses reactivation of fear acquisition neurons by activating or inhibiting neurons tagged during contextual fear conditioning or extinction, DG neurons tagged during fear acquisition were less reactivated in extinction.
    • Experiment 2: Fear retrieval and extinction retrieval activate distinct ensembles of neurons. Extinction retrieval activates neurons tagged during extinction training. Spontaneous recovery reactivates neurons tagged during fear acquisition. Fear and extinction memories are represented by distinct DG neuronal populations, activated depending on fear or extinction memory expression.
    • Experiment 3: Silencing extinction-tagged neurons impairs extinction retrieval; it increases freezing during initial light exposure, but does not affect behavior in neutral contexts or during spontaneous recovery for extinction retention.
    • Experiment 4: Silencing fear acquisition-tagged neurons reduces spontaneous recovery of fear
    • Experiment 5: Stimulating fear acquisition neurons increases fear expression, while stimulating extinction neurons suppresses fear.

    Discussion

    • Extinction training suppresses reactivation of fear acquisition neurons and recruits a different set of neurons (extinction neurons).
    • Silencing fear acquisition neurons reduces fear response, while silencing extinction neurons increases fear response after extinction.
    • Optogenetics (stimulating fear acquisition and extinction neurons) produced different fear responses
    • The dentate gyrus (DG) may be crucial for fear extinction recovery.
    • Stimulation of CFC or extinction neurons showed that distinct engrams (sets of neurons) represent fear and extinction.

    Schemas and Memory Consolidation

    • Mental schemas are frameworks of knowledge crucial for inference, understanding, and prediction.
    • They help process information rapidly and enhance memory encoding and retrieval.
    • Existing schemas can accelerate memory consolidation of new information.
    • Schemas are built from prior experiences and knowledge, allowing us to quickly process and integrate new information and understand and remember complex information better with a relevant mental schema.

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    Lacagnina & Tse Summary PDF

    Description

    This quiz explores the complex mechanisms of fear memory, focusing on the role of hippocampal engrams and the processes of extinction and relapse. It delves into the importance of the prefrontal cortex and the use of transgenic models in understanding these phenomena.

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