Week 4 - Learning/Memory Flashcards
(29 cards)
Learning, memory, and Amnesia
Memory as reconstruction
- Memory is a reconstruction shaped by meaning and expectation. We recall the gist more than details.
Learning, memory, and Amnesia
Memory as adaptive
- Memory helps anticipate and prepare for future events; it is prospective, not just retrospective.
Learning, memory, and Amnesia
3 broad types of long-term memory
- Explicit (conscious): episodic, semantic.
- Implicit (unconscious): skills, habits, priming.
- Emotional: both conscious and unconscious components.
Learning, memory, and Amnesia
Short-term memory
Supports temporary sensory/motor storage.
Learning, memory, and Amnesia
Memory fallibility and bias
- memory errors can arise from favouring one aspect (gist, emotion) over others (details).
- Priming (implicit memory) = prior exposures sensitises memory, altering perception or recall.
- Perception influences memory too.
Learning, memory, and Amnesia
Evidence from early cases
Varieties of amnesia
- Confirmed temporal lobes role in memory.
- Distinct memory contributions from different temporal lobe subregions.
- Area TE damage interferes with conscious recall, with more damage meaning more severe amnesia.
Learning, memory, and Amnesia
Childhood (infantile) amnesia
Varieties of Amnesia
The inability to recall early life events (infancy to early childhood).
Likely causes:
* Memory systems mature at different rates.
* Early episodic memory systems (hippocampus) are not yet developped.
* Neurogenesis in hippocampus may disrupt existing circuits, contributing to memory loss.
* Observed in animals too = species with early hippocampal development do not show infantile amnesia.
Learning, memory, and Amnesia
Amnesias rare and common
Varieties of Amnesia
Fugue state, category-specific Amnesias, everyday forgetting, Alzheimer’s disease.
Fugue state:
* Sudden and transient, usually temporary loss of personal identity/history.
* Often leaves language and learned skills intact.
* Possibly due to suppression of medial-temporal-lobe systems.
Category-specific Amnesias:
* Patients may loss memory for nouns but not verbs, or animals but not tools.
Everyday forgetting:
* “Senior moments” - forgetting names, faces, or where things are placed.
* Increases with age and can become severe (AD)
Alzheimer’s disease:
* Starts with medial temporal lobe damage and expands.
* Characterised by progressive memory loss and neuron degeneration.
Learning, memory, and Amnesia
H.M’s case
Anterograde and retrograde Amnesia
Anterograde amnesia = inability to form new memories after brain injury.
* Also called global anterograde amnesia when all aspects of memory formation are affected.
* H.M could not remember new people or events post-surgery.
* He is impaired in: spatial and topographical learning, learning personal events and vocabulary acquisition.
Retrograde amnesia = loss of memories before the injury.
* Time-limited: older memories often preserved better than newer ones.
* He remembered who he was, how to read, write, speak, childhood home location, and skills learned before surgery.
* Key point: this improves for events that happened earlier in life but recent memories (close to the injury) are more vulnerable.
Learning, memory, and Amnesia
Time dependent retrograde Amnesia
Seen in traumatic brain injury (TBI).
Retrograde memory loss is typically:
* Shrinking over time (older memories are retained more).
* Extent depends on injury severity.
It may include:
* A brief loss of consciousness and confusion.
* Memory gap covering the moments before the injury.
* Often, only a few seconds to minutes of memory are lost long-term.
Learning, memory, and Amnesia
System consolidation theory
Three theories of Amnesia
Core idea: the hippocampus consolidates new memories, eventually making them permanent by transferring them to other brain areas (ex: neocortex).
Key points:
* New memories are initially stored in the hippocampus.
* Over time, they’re consolidated elsewhere (ex: neocortex).
* Older memories survive hippocampal damage because they’ve already been transferred.
* Recent memories are more vulnerable because they’re still in the hippocampus.
* Lesion size affects how far back retrograde amnesia extends: small lesion = few years of loss, large lesion = decades of memory loss).
Learning, memory, and Amnesia
Multiple-trace theory
Three theories of Amnesia
Core idea: memories of all types are stored in parallel across different brain areas.
Key principles:
* Different memory types -> different brain areas.
* Autobiographical -> hippocampus + frontal lobes.
* Factual semantic -> temporal lobe structures.
* General semantic -> cortical areas.
Memory changes over time:
* Memories are recalled, re-evaluated, and stored again.
* This transforms them from autobiographical -> semantic -> generalised.
Memory is distributed and redundant:
* Older memories have more traces, so they’re more resistant to brain injury.
* Different kinds of memory = differently vulnerable to damage.
Learning, memory, and Amnesia
Reconsolidation theory
Three theories of Amnesia
Core idea: every time a memory is recalled, it becomes labile (fragile) and must be reconsolidated, often in a slightly altered form.
What happens during reconsolidation:
* A new memory trace is created each time a memory is used.
* The memory is re-encoded, possibly with distortions.
* Results in many versions of the same memory.
Implications:
* Reconsolidation complicates memory study in amnesia.
* Witnesses, for example, may recall multiple versions of an event.
* Childhood amnesia = hard to tell which memories are original vs reconstructed from repetition or suggestion.
Learning, memory, and Amnesia
Conclusion
Three theories of Amnesia
- Memory is not stored in one place, nor is it static.
- Each theory captures a different aspect of how anterograde and retrograde amnesia work, and together they explain individual variation in memory loss after trauma.
Learning, memory, and Amnesia
Long-term explicit memory
Long-term explicit memory
Explicit memory (declarative memory) is conscious and intentional.
It includes:
* Episodic memory = personal experiences/events.
* Semantic memory = facts and general knowledge.
It relies on top-down processing = how data is organised at encoding influences recall.
Learning, memory, and Amnesia
Episodic (autobiographical memory)
Long-term explicit memory
- Involves personal recall of specific life events.
- Centered around the self = a timeline of personal life history.
- It requires autonoetic awareness = the awareness of the self in subjective time (mental time travel).
- Brain regions: medial temporal lobe, ventral prefrontal cortex, uncinate fasciculus (white matter pathway connecting the two).
Learning, memory, and Amnesia
Autonoetic awareness of time
Long-term explicit memory
It links episodic memory with a sense of personal continuity over time.
Loss leads to:
* Disconnection from past and future.
* Difficulty imaging future scenarios.
Case study - K.C:
* Severe TBI = damage to medial temporal lobes and surrounding areas.
* Retained IQ, semantic knowledge and short-term memory
* Lost all autobiographical memory (past or future) and the ability to “travel time”.
Learning, memory, and Amnesia
Semantic memory
Long-term explicit memory
- Non-personal knowledge: vocab, facts, reading, maths, names of people/faces and recognition of family, historical knowledge.
- It does not rely on the same network as episodic memory.
- It is supported by temporal and frontal lobe regions adjacent to (but not the same as) episode system.
Learning, memory, and Amnesia
Key brain regions involved
Neural substrates of explicit memory
Temporal-frontal system is the proposed core for explicit memory.
Key structures:
* Hippocamus
* Rhinal cortices (entorhinal, perirhinal).
* Prefrontal cortex
* Thalamus (especially medial nuclei).
These regions interact heavily via the thalamus and receive input from:
* Neocortex
* Ascending systems => acetylcholine, serotonin, noradrenaline.
Learning, memory, and Amnesia
Hippocampal anatomy
Neural substrates of explicit memory
Key structures:
* Ammon’s horn = contains pyramidal cells (CA1, CA2, CA3, CA4).
* Dentate gyrus = contains granule cells.
* Subiculum = acts as output zone.
* Entorhinal cortex = input/output gateway to the hippocampus.
Pathways:
* Perforant pathway = connects neocortex to hippocampus.
* Fimbira fornix = connects hippocampus to the basal ganglia, thalamus, and hypothalamus (lesions here leads to amnesia without direct hippocampal damage).
Learning, memory, and Amnesia
Hippocampal function
Neural substrates of explicit memory
Core roles from hippocampal patients:
* Anterograde memory is more severely impaired than retrograde memory.
* Episodic memories is mre vulnerable than semantic memories.
* Autobiographical memory (linked to “time travel” is most severely affected.
Supporting evidence:
* Hippocampus integrates multiple inputs to support episodic memory.
* Anterior hippocampus = coarse memory representation.
* Posterior hippocampus = fine-grained details.
Learning, memory, and Amnesia
The temporal cortex
Neural substrates of explicit memory
Temporal areas bordering the rhinal fissure include:
* The perirhinal cortex and the entorhinal cortex: they provide major route for neocortical input to the hippocampal formation.
* Lesions here affect object recognition and contextual recall.
Learning, memory, and Amnesia
Experiment evidence
Neural substrates of explicit memory
Monkey experiments:
* Perirhinal cortex = crucial for object recognition (semantic memory)
* Hippocampus = critical for context-based recall (episodic memory).
Human fMRI:
* Perirhinal cortex = active for object recognition.
* Hippocampus = active for recalling personally known facts.
Learning, memory, and Amnesia
Hemispheric specialisation of explicit memory
Hemispheric specialisation of explicit memory
- Explicit memory shows lateralised processing across both hemispheres ofthe temporal, parietal, occipital, and frontal lobes.
- Removal of one hemisphere’s temporal lobe reveals asymmetrical memory deficits.
