Memory Systems
Isabelle Rapin
Seminar in Developmental Disabilities
February 20, 2013
No conflict of interest
Multiple Memory Systems
 Short term memory systems
• Sensory buffers (for each modality +
•
endogenous inputs from memory)
Working memory
 Long term memory systems
• Declarative (or explicit)
• Non-declarative
 Retrieval systems
1. Schema of STM systems
Short Term Memory
Sensory buffers
Working memory
Sensory cortices
Prefrontal cortex
Short Term Memory
 Components: buffers + working memory
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Sensory buffers: in continuous on-line reciprocal
contact with working memory circuitry
Working memory: processes only information that
reaches awareness, does so in the light of other
inputs and priorities*
 Duration range: < 1 - few seconds
 Requirement: repeated inputs or rehearsal
 Fate: erasure or potential storage
*Information that does not reach awareness may have
non-declarative priming effects
Working Memory Circuitry
 Prefrontal cortex: in continuous on-line
reciprocal connections with
• Sensory cortices for each modality (specific buffers)
• Limbic circuits
• Arousal circuits
• Motor output circuits
***
 Note: Hippocampus circuitry: (data from amnestic
patients)
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Not critical on-line,
Critical for long term storage
LTM declarative systems
Declarative (or explicit)
memories
Episodic memory
(time-bound facts of the
individual’s past)
Medial temporal cortices +
Semantic memory
(knowledge of
the world)
Medial temporal cortices +
Declarative (explicit) Memory
1. Episodic
(Tulving)
 Uniquely human capacity to look back to the
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past and predict the future
Powerful tool
Retrieve specific facts/events in time/place
context (unique, autobiographical)
Late to develop evolutionarily (man only?) and
ontogenitically (infant amnesia)
Fragile to degeneration
Critically dependent on (not limited to!)
hippocampal/medial temporal cortices
Declarative (explicit) Memory
2. Semantic Memory
 Knowledge (as opposed to remembrance
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of specific facts)
“Picked-up” knowledge from exposure to
mostly forgotten past events/experiences
Starts at birth, long before episodic
memory
Broad and powerful
Much more resilient than episodic memory
2 - LTM non-declarative systems
Non-declarative (implicit)
memories/learning nodes
Procedural
(skills, habits)
Priming
Conditioning
Basal ganglia
(putamen), etc.
Sensory cortices
Emotional: amygdala
Motor: cerebellum +
Non-associative
Reflex pathways
Hippocampus system
 Binds inputs from all sensory modalities
with limbic and prefrontal executive inputs
 Reciprocally connected with relevant
cortical and subcortical circuitry
 Required for declarative memory
• For fresh and midterm declarative memories
• Not for very long term
“
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 Not required for non-declarative memories
Brain molecular/cellular
underpinnings of memory
(Kandel, etc.)
 Molecular – short term manipulation of incoming
information to guide on-going behavior
•
Alteration in strength/effectiveness of already existing
synapses
 Neurotransmitter release/uptake
 Cellular – long term storage
•
Requires protein synthesis and growth of new
 synaptic receptors
 dendrites
 Brain circuitry – long-term (yrs) consolidation
Retrieval
 Long-term explicit memory storage:
• mainly in modality-specific relevant
neocortical, ± limbic areas
 Recognition -- cue, strong, bottom-up
 Retrieval of unique item -- top/down, effortful
 Long-term implicit memory storage:
• mainly in cortical/subcortical circuitry relevant
to task/skill performance (e.g., motor cortex,
basal ganglia, cerebellum, brainstem, spinal
cord)
Amnestic syndrome
 Result of bilateral hippocampal damage
 Not necessarily irreversible except for peri
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lesional time-window
Impairs new explicit learning
Impairs explicit but not implicit memories
Does not impair procedural memory/skills
Does not preclude learning new skills!
Occasional cases in kids, even infants
Evidence for neural circuitry of
memory
 Lesion studies
• Behavioral evidence
• Imaging
• Autopsy
 Electrophysiology
 Functional imaging (PET, fMRI…)
 Subtraction: task vs. no task (“rest”)
 Subtraction: impaired group vs. “typical”
group
Problems with functional studies
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Smallness of samples
Homogeneity of samples
Failure to replicate
Multiplicity of nodes in widely distributed
pathways
Requirement for cooperation
Great difficulty/impossibility of testing young
children
Cost
Time required for data analysis
Fancy statistical analyses required