What are declarative and non-declarative memory?

Declarative and Non-Declarative Memory

Declarative memory refers to conscious, explicit memory for facts and events that can be verbally described, while non-declarative memory encompasses unconscious, implicit memory systems including skills, habits, priming, and conditioning that influence behavior without conscious awareness.

Declarative Memory (Explicit Memory)

Declarative memory is the memory system that supports conscious recollection and can be intentionally retrieved and verbally expressed 1, 2.

Two Main Components:

• Episodic memory: Memory for personal experiences and specific events that occurred at particular times and places 2, 3
• Semantic memory: Memory for general knowledge, facts, and concepts independent of personal experience 2, 3

Neural Substrates:

• The medial temporal lobe system, particularly the hippocampus and related structures in the parahippocampal gyrus, is essential for declarative memory formation and retrieval 1, 2
• The perirhinal cortex contributes to both episodic and semantic memory by representing associations between items, rewards, places, and temporal information 4
• The entorhinal cortex serves as an interface, providing item and context information to the hippocampus 4

Key Characteristics:

• Declarative memory involves constructive and reconstructive processes rather than literal reproduction of past events 5
• Memory encoding is influenced by present knowledge, beliefs, and previous experiences 5
• Each recall episode triggers reconsolidation, irretrievably changing the original memory 5

Non-Declarative Memory (Implicit Memory)

Non-declarative memory encompasses multiple unconscious memory systems that influence behavior without requiring conscious awareness or verbal description 1, 6.

Components Include:

• Motor, perceptual, and cognitive skills: Learned abilities that improve with practice 6, 2
• Habits: Automatic behavioral patterns 1, 2
• Priming: Enhanced processing of previously encountered stimuli 6, 2
• Simple conditioning: Basic associative learning including classical and operant conditioning 1, 6
• Non-associative learning: Habituation and sensitization 6

Neural Substrates:

• The basal ganglia support motor and cognitive skill acquisition 6
• The cerebellum is critical for certain types of classical conditioning and motor learning 6
• The striatum contributes to habit formation 2
• The neocortex supports various forms of perceptual and cognitive skill learning 2

Critical Distinctions

Dissociation Evidence:

• Damage to medial temporal or medial thalamic regions produces severe declarative memory deficits while largely sparing non-declarative memory 6
• Experimental manipulations and pharmacological agents can differentially affect these two memory systems 6
• Patients with amnesia from hippocampal damage cannot form new declarative memories but retain the ability to acquire new skills and show normal priming effects 1, 2

Operating Characteristics:

• Declarative memory requires conscious, effortful retrieval processes, while non-declarative memory operates automatically without conscious awareness 1, 6
• Non-declarative memory influences behavior even when the original learning episode is not consciously remembered 6
• The two systems have different acquisition rates, retention characteristics, and susceptibility to interference 1

Clinical Implications

Common Pitfalls:

• Assuming that all memory deficits reflect a unitary system—different brain lesions produce dissociable patterns of declarative versus non-declarative memory impairment 6, 2
• Relying on declarative memory reports as literal, accurate reproductions of past events when they are actually constructive processes prone to distortion 5, 7
• The process of repeated questioning can alter memories through reconsolidation, making each subsequent recall less reliable 5, 7