Seminar in Developmental Disabilities 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 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) 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) Semantic memory (knowledge of the world) Medial temporal cortices + Medial temporal cortices +

Declarative (explicit) Memory 1. Episodic (Tulving) Uniquely human capacity to look back to the 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 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 Non-associative Basal ganglia (putamen), etc. Sensory cortices Emotional: amygdala Motor: cerebellum + 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 “ “ 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-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 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