3.1.1 learning & memory I

1. Diagram the Three-Stage Model of Memory, Outlining How Information Moves from Sensory Memory to Working Memory to long-term memory, and noting the Capacity/Duration of Each Memory Store

• Foundational Distinction:

  • Learning: The process of acquiring new knowledge, behaviours, or skills.

  • Memory: The persistence and retention of learned information over time for subsequent retrieval.

  • Information moves from sensory to working memory with attention, from working memoery to long-term memory with encoding.

• Sensory Memory Store:

  • Capacity: Large

  • Duration: Extremely transient ($< 1\,\text{s}$ for iconic traces; up to several seconds for echoic traces).

  • Function: Temporarily buffers raw, unprocessed sensory inputs for pre-attentive analysis before discarding or transferring.

  • Information Flow & Control Process:

    • Selective attention acts as a filter, transferring attended input (sensory information) to working memory while unattended information decays and is permanently lost.

• Working Memory Store (Short-Term Workspace):

  • Capacity: Small and limited, classically quantified as $7 \pm 2$ items or chunks.

  • Duration: Approximately $20\,\text{s}$ without active rehearsal.

  • Function: Dynamic mental workspace for actively holding and manipulating conscious information.

    • Maintenance Strategies: Information is prolonged via maintenance rehearsal or expanded in effective capacity via chunking.

    • Primarily relies on the prefrontal cortex, supported by premotor, supplementary motor, and lateral interparietal cortices.

• Long-Term Memory Store:

  • Capacity: Essentially unlimited.

  • Duration: Enduring, persisting across days, years, or a lifetime.

  • Information Flow & Control Process: Information transitions from working memory into long-term storage via encoding.   

    • Encoding is either automatic (driven by personal or emotional relevance) or effortful (requiring active rehearsal and elaborative organisation).

2. Compare and Contrast the Different Types of Declarative Memory

• Broad Division of Long-Term Memory:

  • Declarative (Explicit) Memory: Involves conscious recollection; rapid to form, but vulnerable to forgetting.

  • Non-Declarative (Implicit) Memory: Unconsciously expressed through performance and action; acquired gradually through practice and highly resistant to decay (e.g., motor skills, conditioning, priming).

• Comparison of Declarative Memory Subtypes:

  • Episodic Memory:

    • Definition: Memory for personally experienced autobiographical events.

    • Contextual Anchoring: Tied to a specific time, place, and situation ("when" and "where" an event occurred).

  • Semantic Memory:

    • Definition: General factual knowledge, vocabulary, concepts, and rules about the world.

    • Contextual Anchoring: Context-free and independent of the original time, setting, or episode in which it was learned.

3. Discuss the Role of the Hippocampus and Associated Structures in the Encoding, Consolidation and Storage of Declarative Memories

• Medial Temporal Lobe Circuitry and Information Routing:

  • Key Anatomical Structures of the Medial Temporal Lobe memory system:

    • hippocampus

    • entorhinal

    • perihinal

    • parahippocampal corticies

  • The physical location of a memory is called an engram

  • Perforant Pathway (information flow): Neocortical association areas → parahippocampal/perirhinal cortices → entorhinal cortex → perforant pathway → hippocampus (tri-synaptic circuit) → fornix → diencephalon, then projecting back via entorhinal cortex to neocortex.

  • Convergence and Binding Function: The hippocampus acts as a hub, binding distributed sensory features into a single, cohesive representation.

• Phases of Declarative Memory Processing:

  • Encoding: The process of transforming perception, thought or feeling into a memory

  • Consolidation: Stabilises fragile, hippocampus-dependent memories into enduring traces, gradually transferring reliance from the hippocampus to distributed neocortical networks via systems consolidation.

  • Storage: Permanent long-term storage of declarative memories resides within distributed neocortical association networks rather than within the hippocampus itself.

  • Reconsolidation: Reactivating a memory makes it temporarily labile and susceptible to disruption, requiring protein synthesis to restabilise.

4. Compare and Contrast Anterograde vs. Retrograde Amnesia and Describe How Lesions to the Hippocampus and Associated Structures Lead to These Changes

• Comparing and Contrasting Amnesic Profiles:

  • Anterograde Amnesia: An inability to form or consolidate new declarative memories following a neurological insult; memories cannot move from working memory into long-term storage.

  • Retrograde Amnesia: The loss of declarative memories that were formed prior to the neurological insult.

  • Temporal Grading (Ribot's Law): Retrograde amnesia exhibits a temporal gradient: older memories are preserved because they completed cortical consolidation, whereas recent, hippocampus-dependent memories are lost.

• Effects of Lesions to the Hippocampus and Medial Temporal Lobe:

• The medial temporal lobe: required for declarative memory

• The medial diencephalon: relay for declarative memory consolidation

Patient H.M. (Henry Molaison):

• Bilateral medial temporal lobectomy (hippocampus, entorhinal cortex, amygdala):

  • Results in severe anterograde declarative and temporally graded retrograde amnesia.

• Isolated hippocampal damage:

  • Causes mild declarative impairment.

    • Lesions extending from hippocampus into surrounding medial temporal cortices produce progressively severe amnesia.

Patient N.A.: Sustained a penetrating fencing foil injury through the right nostril

• Left dorsomedial nucleus lesions of the thalamus

  • Severe anterograde declarative amnesia and roughly two years of retrograde amnesia.

• Korsakoff's Syndrome:

  • Etiology: Thiamine ($\text{vitamin B}_1$) deficiency, typically secondary to chronic alcohol use disorder.

    • Bilateral atrophy of the mammillary bodies and dorsomedial thalamus:

      • disrupts the mammillothalamic tract while sparing the hippocampus:

        • causes severe anterograde amnesia, confusion, and confabulation (fabricating false memories).

• Alzheimer's Disease:

  • Neuropathology: Progressive neurodegeneration beginning in the entorhinal cortex and hippocampus

    • characterised by extracellular amyloid beta ($A\beta$) plaques and intracellular neurofibrillary tangles (hyperphosphorylated tau).

  • Leisons to entorhinal cortex and hippicampus:

    • Causes early episodic memory loss and dense anterograde declarative deficits