Midterm Questions Flashcards
Compare and contrast ingrams and engrams and give a novel example of each.
Both are memories stored within the body:
— Ingrams: intrinsic memories, do not need to be learnt; i.e. reflexes
— Engrams: extrinsic memories, learned by the individual; i.e. knowing how to write
Explain the importance of Hermann Ebbinghaus’ contributions to the science of human memory.
— He developed the first scientific method for assessing acquisition and retention.
— Methodology that could separate what the subject already has learned from what the subject was now being asked to remember.
— The nonsense syllable
— Ebbinghaus’s forgetting curve: describes how we retain memory
⇒ how information is forgotten over time when there is no attempt to retain it
⇒ decline in retention after first learning something
— Provided an understanding of learning and memory retention, and a framework for studying the subject.
— Inspired single trace and dual trace theories
What is the neuron doctrine? Briefly describe the historical context in which it emerged and broadly outline its relevance for human memory.
— Describes the neuron as an independent unit comprised of the cell-body, axons, and dendrites
— synapses between neurons; neurons are not fused together
— developed due to Golgi’s creation of the Golgi stain (showed that neurons were not fused)
— Cajal improved this method to and inspired the neuron doctrine
Explain what grid cells are and how they work.
— Grid cell play specialized role in navigation and spacial memory
— Grid cells fire at regular intervals as an animal navigates an open area
— firing pattern of these creates a hexagonal lattice that enables an understanding of position in space by integrating and storing information about location, distance, and direction.
— The combination of activity from many grid cells provides a coordinate system or internal GPS, allowing for precise spatial navigation and the ability to navigate complex environments by encoding spatial relationships and directions
— Allocentric navigation
— found in the brain’s entorhinal cortex
What are Hebbian cell assemblies, and how are they thought to be important for memory formation?
— Hebb: modified ensembles of neurons (cell assemblies) could provide a substrate for memory
— groups of neurons become linked through repetition (leads to faster transmission).
— “cells that fire together, wire together”
⇒ “When an axon of cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A’s efficiency, as one of the cells firing B, is increased.” (Hebb, 1949)
Explain the Bliss and Lømo experiment that led to the discovery of long-term potentiation.
— They conducted their experiment on a live rabbit’s hippocampus, focusing on the perforant path that leads to the dentate gyrus.
— Stimulation: Stimulated the perforant path, which connects the entorhinal cortex to the dentate gyrus of the hippocampus
— Baseline measurement: Initially, a weak stimulus is applied to the perforant path to measure synaptic activity under normal conditions
— Induction of LTP: Following the baseline measurement, a strong stimulus was applied to the same path. This strong stimulus was found to evoke more synaptic activity than the initial weak stimulus.
— Observation:
a. The strong stimulus led to an enduring increase in the synaptic response to subsequent weak stimuli. This enhanced response is called Long-term Potentiation.
b. It indicates that synaptic connections could be strengthened through activity, suggesting a cellular mechanism for learning and memory
c. It demonstrates synaptic plasticity — the ability of synapses to strengthen or weaken over time, in response to increases or decreases in activity. LTP, as observed by Bliss and Lømo, provides a biological basis for the Hebbian principle (“cells that fire together, wire together”), suggesting that memory and learning are encoded through changes in synaptic strength.
Outline the structure of the hippocampus.
Trisynaptic circuit:
1. Neurons in the entorhinal cortex connect to a region in the hippocampus called the dentate gyrus by what is called the perforant path.
2. Neurons in the dentate gyrus connect to the CA3 region by what are called mossy fibres.
3. Neurons in CA3 connect to neurons in the CA1 region by what are called Schaffer collateral fibres.
Why is the hippocampus generally thought to be an important brain structure for memory?
Thought to play role in memory consolidation Lesion studies show damage to hippocampus leads to impairment in forming new memories; other cognitive function intact Neuroimaging studies show increase hippocampal activity during memory-related tasks
Name and describe the three dimensions of memory traces that were outlined in the lecture.
The dimensions of memory traces are:
— duration: length of time a memory trace persists in the brain
⇒ rapid decay: active state
⇒ slow decay: inactive state
— state: Internal and external conditions that were present when memory trace was formed
⇒ active
⇒ inactive
— vulnerability to disruption: Susceptibility of memory traces to interference and distortion
Memory traces can be disrupted by competing info or passage of time, leading to forgetting and inaccurate recalls
⇒ vulnerable to disruption: active state
⇒ less vulnerable to disruption: inactive state
— State is either active or inactive
— active traces are more vulnerable to decay + disruption
— memories that are in an active state are either new or recently retrieved memories, which is why they are more vulnerable. Inactive traces are already consolidated and stored, which makes them less vulnerable.
Compare and contrast the “Levels of Processing” and the “General Abstract Processing System” frameworks for the creation of memory traces.
— Levels: perception processing depth
memory trace: a byproduct of the depth of processing
memory persistence: depends on the analyzed depth
— memory retrieval: depends on attention, compatibility of the analysis structure, time of processing
— Episodic memory
— Memory is separated from the perceptual process
— Encoding: converts events into physical/ synaptic framework, engram.
— Ecphory: combines engram and retrieval cues to make memory retrievable
— Ecphoric information: the end product of cognitive memory
Outline some of the psychological and physiological evidence that suggests encoding is a separate process from perception.
— Psychological phenomenon:
⇒ Interruption of encoding process: memory is weakened or altered if its encoding process is interrupted.
⇒ Anterograde amnesia: Amnesia prevents patients from forming new memories but does not affect normal perceptions.
⇒ False memory: recalled memories can be inaccurate compared to the real event.
⇒ Psychopharmacology: Benzodiazepines do not disable perception, but do affect recall during the active period.
— Brain Scans:
EEG: There’s a different ERP to which a stimulus (words) that are later recalled vs those that are not recalled, the ERP is independent of the perception of the words.
⇒ fMRI: left prefrontal cortex and temporal cortices show activity during encoding of information that can be later recalled. Lesions to these regions impairs memory but not perception.
Briefly describe the experiments by Malinow that demonstrate AMPA receptor trafficking to the synapse. Why is it important for long-term memory formation?
Fear Conditioning induces AMPA trafficking
Inject genetically altered GluA1 into mice’s amygdala with viral vector system. Altered GluA1 has a fluorescent protein labelled and is a subunit of AMPA receptors.
Expose mice to fear conditioning, conditioned mice pair fear to the stimulus and react with freezing.
All mice are euthanized for brain slice collection.
Mice that are conditioned showed more concentration of AMPA with altered GluA1 in the synapse
Dummy AMPA reduces fear conditioning
Altered GluA1 that is not functional is injected into mice’s lateral amygdala. Injected GluA1 is non-functional.
Mice with manipulation cannot sustain normal LTP.
The process of memory consolidation requires two waves of protein synthesis. What condition(s) must be met to initiate the first wave? How can the first wave be disrupted, and what would the behavioural consequence be?
Conditions:
— Local protein synthesis
— involves BDNF and mTOR to produce ribosomes for LTP related protein production.
Disruption:
— Introduce Rapamycin which inhibits mTOR
— disrupts memory recall if introduced before fear avoidance training, both 1 hour and 12 hours after, Since inhibiting 1st wave also inhibits 2nd wave. No disruptive effect if Rapamycin is introduced after training.
The process of memory consolidation requires two waves of protein synthesis. What condition(s) must be met to initiate the second wave? How can the second wave be disrupted, and what would the behavioural consequence be?
Conditions:
— Genomic protein synthesis/Positive feedback autoregulatory loop
BDNF induces self-production 12 hours after training runs for 48 hours
— the loop involves CERB which induce C/EB beta production (9 hours after CERB)
Behavioural consequences:
- inhibition of C/EBPβ 5 hours after training disrupts LTM but resupplying BDNF restores LTM.
- Disrupting LTM prevents the recall of training after 7 days.
What is meant by “memory trace destabilization”? Provide an overview of the phenomenon and briefly identify its role in memory reconsolidation.
“Memory trace destabilization” refers to the process where a previously consolidated memory becomes labile or unstable upon reactivation
This destabilization of the memory trace requires an increase in dendritic spine calcium levels, which can occur through different mechanisms in brain regions like the amygdala and hippocampus
Without calcium influx, trace destabilization does not occur.
During trace destabilization, scaffolding proteins that maintain the structure of synapses are tagged for degradation, and proteasomes move to degrade proteins.
Shank, a crucial scaffolding protein, plays a key role in this process
Disruption of this destabilization process, such as inhibiting proteasome activity, can prevent the degradation of reactivated memory traces.
In memory reconsolidation, destabilization of the memory trace is essential for updating or modifying existing memories
Strong or old memories are more resistant to destabilization, while memories formed under weaker training conditions are more easily destabilized
The prediction error hypothesis suggests that memories become destabilized when they fail to predict or match the current experience
This process allows for the incorporation of new information into existing memories, leading to memory reconsolidation.
