Memory Systems
Human memory is not a single system but a family of distinct, dissociable systems with different timescales, contents, and neural substrates.
Key facts
- Working memory capacity is ~3–4 chunks (Cowan), not 7±2.
- Hippocampus is essential for new declarative memory.
- Sleep is critical for consolidation.
- Memory is reconstructive — every recall changes the trace.
A Taxonomy of Memory
Working memory holds information briefly for manipulation. Long-term memory divides into declarative (episodic and semantic) and non-declarative (procedural, priming, conditioning) systems.
- Working memory — seconds to minutes, severely capacity-limited.
- Episodic memory — autobiographical events with context.
- Semantic memory — facts and concepts.
- Procedural memory — skills and habits.
Encoding and Consolidation
New memories are initially hippocampus-dependent, gradually consolidating into distributed cortical traces — a process accelerated by sleep, especially slow-wave and REM phases.
Memory Is Reconstructive
Recall is not playback. Each retrieval reactivates and partially rewrites the trace, making memory susceptible to suggestion, source confusion, and confabulation.
This has major implications for eyewitness testimony and therapeutic practice.
Frequently asked
Why do we forget?
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Forgetting reflects decay, interference, and reconsolidation failures — and serves adaptive functions like generalization.
Can memories be implanted?
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Yes, false memories can be induced experimentally — a well-documented and widely replicated finding.
Sources & further reading
Continue in this series
Biological Substrate
The Neuron and the Brain
Sensory Cognition
Perception and Attention
Higher Cognition
Reasoning and Decision-Making
Communication
Language and Symbolic Thought
Subjective Experience
Consciousness: The Hardest Problem
Psychometrics
Intelligence and IQ