Free explainer4 min read
Memory systems
Understand the model, recognise it in a stem, separate the look-alikes, then apply it.
Start with the mental model
Because damage to one brain region can erase new facts while leaving old skills and habits intact, memory is not one system but several dissociable ones: declarative memory (facts and events consciously recalled) and non-declarative memory (skills and habits performed without conscious recall). This split matters clinically because a bedside test of one system can look normal while the other is silently impaired. Working memory (a short-term, prefrontal system that holds and manipulates information for seconds) sits apart from both long-term stores.
Watch it explainedHe got better at the task every single day. Every day he said he had never seen it.
Visual explanationUse the diagram to rebuild the concept from memory.
01Core model
Declarative memory divides into episodic memory (personally experienced events tied to time and place) and semantic memory (context-free facts), and both depend on the hippocampusA brain structure central to forming new memories.Read more → and medial temporal lobeThe part of the brain by the ears, involved in hearing, language and memory.Read more → to encode new material, the region destroyed in the amnesic patient H.M. Non-declarative memory, covering procedural skills, priming, and classical conditioning, depends instead on the basal gangliaA group of deep brain structures that help control movement and are affected in Parkinson's disease and by antipsychotic drugs.Read more → and cerebellumThe brain structure at the back of the skull that coordinates balance and smooth movement.Read more → and survives even total hippocampal loss. Working memory itself has three parts under Baddeley's model: the central executive (the attention-controlling manager), the phonological loop (a verbal rehearsal buffer), and the visuospatial sketchpad (a buffer for images and spatial layout). E.g., a patient who cannot recall breakfast an hour later (hippocampal loss) can still repeat a phone number back correctly (working memory intact), because the two systems sit in different circuits.
02Recognise it in an SBA
• A patient with hippocampal damage recalls the last few words of a list normally but poorly recalls the first few words (the primacy effect). Which explanation fits best?
03Separate the look-alikes
| Declarative (explicit) memory | consciously recalled facts and events, unlike procedural memory for skills accessed without awareness. |
|---|---|
| Episodic memory | personally experienced events tied to time and place, whereas semantic memory holds context-free general facts. |
| Working memory | brief online holding and manipulation of information, rather than durable long-term storage. |
| Procedural memory | motor and habit learning spared in amnesia, unlike the episodic loss of hippocampal damage. |
| Iconic memory | a distinct, millisecond-scale sensory memory system holding a brief visual afterimage of a stimulus, unlike working memory, which holds and manipulates information over seconds. |
How the exam thinksRead the question the way the examiner wrote it.
What people get wrong here
• The phonological loop supports brief verbatim retention of the most recent items, not the long-term storage needed for earlier list items.
• Procedural memory supports motor and skill learning and is characteristically preserved, rather than most affected, in hippocampal amnesia.
• Both early and late list items can be encoded semantically; the primacy effect reflects consolidation timing, not a different encoding type.
• Attention is generally intact in focal hippocampal amnesia, so reduced attention alone does not explain the selective loss of primacy.
Deep diveStart from scratch, the full, beginner-friendly explanation.
**Sort every memory question by asking whether the information is consciously recalled (declarative memory) or performed without conscious recall (non-declarative memory), since each system depends on a different brain circuit**. Declarative memory further splits into episodic memory (personal events) and semantic memory (facts), both encoded by the hippocampusA brain structure central to forming new memories.Read more →, while non-declarative memory covers procedural skills, priming, and conditioning, carried by the basal gangliaA group of deep brain structures that help control movement and are affected in Parkinson's disease and by antipsychotic drugs.Read more → and cerebellumThe brain structure at the back of the skull that coordinates balance and smooth movement.Read more →. Working memory (the short-term, prefrontal system holding information for seconds while you use it) is a separate third system, distinct from both long-term stores. Clinically, a patient with hippocampal damage cannot form new declarative memories but can still learn a new motor skill through repeated practice, so memory testing must probe more than one system to avoid missing a selective deficit.
01Memory divides into declarative
Memory divides into declarative (explicit), episodic (personal events) and semantic (facts), and non-declarative (implicit), procedural (skills), priming, conditioning.
02Declarative memory depends on
Declarative memory depends on the medial temporal lobeThe part of the brain by the ears, involved in hearing, language and memory.Read more →/hippocampusA brain structure central to forming new memories.Read more → (lost in amnesia, e.g. patient H.M.), whereas PROCEDURAL memory depends on the basal gangliaA group of deep brain structures that help control movement and are affected in Parkinson's disease and by antipsychotic drugs.Read more → and cerebellumThe brain structure at the back of the skull that coordinates balance and smooth movement.Read more → and is SPARED in medial temporal damage (an amnesic can still learn a motor skill without recalling the practice).
03Working memory is a
Working memory is a separate prefrontal short-term system.
Worked application
Worked application: A patient with hippocampal damage recalls the last few words of a list normally but poorly recalls the first few words (the primacy effect). Which explanation fits best? The best answer is “Early items depend on transfer into long-term memory, which needs an intact hippocampusA brain structure central to forming new memories.Read more →.” because Early list items are rehearsed and consolidated into long-term memory, a hippocampus-dependent process that fails in amnesia, abolishing the primacy effect.
The story in picturesPredict each next frame before you reveal it.
04Question-solving strategy
• Localise the clue to the relevant anatomical level, cell type, pathway or molecular process.
• Map that structure or process to its normal function.
• Predict the deficit or clinical sign produced when it is disrupted.
• Reject options that belong to a neighbouring structure, pathway or level of explanation.