PSYC10003 · Mind, Brain and Behaviour 1
Long-Term Memory and The Amnesias
Week 4 also maps the structure of long-term memory — the explicit/declarative (episodic, semantic) versus implicit/non-declarative (procedural, priming) distinction — and how memories consolidate. It uses anterograde and retrograde amnesia and the landmark case of patient H.M. to link memory systems to the medial temporal lobe and hippocampus. The examinable skill, within the 25% Learning & Cognition block, is using a patient's spared-versus-impaired profile as evidence for which memory system a task engages and where the lesion sits.
What this chapter covers
- 01Declarative (explicit) memory: episodic (personal events) vs semantic (facts/concepts); MTL/hippocampus-dependent
- 02Non-declarative (implicit) memory: procedural skills and priming; not hippocampus-dependent
- 03Explicit vs implicit as a property of the retrieval mechanism (conscious recollection vs performance change)
- 04Consolidation: hippocampus-dependent memories gradually become cortical and independent over time
- 05Retrograde amnesia (loss of pre-injury memories; temporally graded) vs anterograde amnesia (cannot form new memories)
- 06Patient H.M.: bilateral medial-temporal removal → dense anterograde amnesia + graded retrograde amnesia
- 07H.M.'s dissociation: intact procedural learning (mirror-tracing) despite no conscious recollection
- 08Evidence that declarative and non-declarative memory rely on different neural systems
Reading a lesion profile as evidence
- +1(a) The inability to form new memories after the injury is anterograde amnesia (failure to consolidate new declarative memories).
- +1(b) Steady improvement on the mirror-tracing skill is non-declarative (procedural) learning — a motor skill expressed as improved performance without conscious recollection. The patient's denial of ever doing the task shows the declarative memory of the episode is absent while the procedural memory is intact.
- +1(c) Spared remote (childhood) memories with impaired recent ones is temporally graded retrograde amnesia. It indicates that older memories have been consolidated into cortex and become independent of the medial temporal lobe, whereas recent memories still relied on it.
- +1Draw the inference. The medial temporal lobe / hippocampus is required to consolidate new declarative memories but is not the permanent store; over time consolidation forms direct cortical links. The declarative-vs-procedural dissociation shows the two systems rely on different neural structures.
Key terms
- Declarative (explicit) memory
- Consciously recollected 'knowing what' — episodic memory for personal events and semantic memory for facts and concepts; dependent on the medial temporal lobe and hippocampus.
- Non-declarative (implicit) memory
- 'Knowing how' expressed as a change in behaviour without conscious recollection — procedural skills and priming; relies on structures outside the medial temporal lobe.
- Episodic vs semantic memory
- Two kinds of declarative memory: episodic is memory for personally experienced, time- and place-tagged events ('mental time travel'); semantic is general factual knowledge abstracted from context.
- Consolidation
- The process by which newly encoded, hippocampus-dependent memories gradually form direct cortical connections and become independent of the medial temporal lobe over time.
- Anterograde amnesia
- The inability to consolidate new declarative memories for events occurring after a brain injury, with short-term and procedural memory typically spared.
- Retrograde amnesia
- Loss of memories formed before an injury, usually temporally graded so that recent pre-injury memories are most affected and remote memories are relatively spared.
Long-Term Memory and The Amnesias FAQ
What is the difference between episodic and semantic memory?
Episodic memory is for personally experienced events situated in time and place — recalling sitting in a particular lecture. Semantic memory is general knowledge stripped of the learning context — knowing a concept from that lecture without recalling the lecture itself. Both are declarative and both draw on the medial temporal lobe.
Why is patient H.M. so important?
His bilateral medial-temporal removal produced dense anterograde amnesia (no new declarative memories) alongside intact short-term, procedural and remote memory. This double dissociation showed the medial temporal lobe is essential for forming — but not permanently storing — declarative memories, and that declarative and non-declarative memory are separate systems.
How can someone learn a skill but not remember learning it?
Because procedural (non-declarative) memory relies on different neural structures from declarative memory. H.M. improved on mirror-tracing across days (procedural learning intact) while having no conscious recollection of the sessions (declarative memory impaired) — direct evidence the two systems are dissociable.
What does 'temporally graded' retrograde amnesia mean?
It means the loss is worst for memories formed just before the injury and progressively spares older memories. This gradient is evidence for consolidation: older memories have moved to cortex and no longer depend on the damaged medial temporal lobe.
Is priming declarative or non-declarative?
Non-declarative. Priming is a change in the speed or accuracy of processing a stimulus due to prior exposure, without conscious recollection — measured indirectly with tasks like lexical decision. It is preserved in amnesic patients who cannot consciously recall the priming episode.
Exam move
Draw the taxonomy tree of long-term memory (declarative → episodic/semantic; non-declarative → procedural/priming) and tag which branch depends on the medial temporal lobe. Practise the patient-evidence move on fresh vignettes: name the spared system, name the impaired system, and state what the dissociation proves. Keep anterograde (can't form new) and retrograde (lost old, graded) straight, and be able to explain the graded pattern via consolidation. Because the exam tests findings not names, revise H.M. as a reasoning chain rather than a biography. Confirm exam details on Canvas.
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