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Building Memories: Remembering and Forgetting of
Verbal Experiences as Predicted by Brain Activity
Research by Wagner et alPresented by Daehan Choi
The Big Picture - Memory EncodingHow come we remember some things and
forget others?Neurological basis?
Differences in brain activation?
WHAT IS GOING ON IN THE BRAIN?
Memory EncodingWhat is Memory Encoding?
processes by which an experience is trans-formed into an enduring memory trace.
influenced by the cognitive operations engaged during initial encoding of that experience
semantic processing leading to superior mem-orability
relative to nonsemantic processing
Previous Functional neuro-imagingLeft prefrontal activation in verbal tasks
greater during semantic relative to nonsemantic verbal task
Activation decreases and memorization is impaired when semantic encodings are disrupted
SO BASICALLY LOOKING PROMISING THERE
Objective of the StudyThe study examines the neural correlations of
incidental word encoding in two whole-brain function-al magnetic resonance imaging (fMRI) studies.
Method/ResultsOne experiment used blocked-design
to investigate how systematic manipulation of the encoding task affects prefrontal and medial temporal activation
Another used newly developed event-related procedures (ERP)allow direct comparison between specific en-
coding trials that result in subsequent remem-bering and forgetting.
Blocked Design ExperimentActivation during a semantic processing task
was compared to that of nonsemantic
semantic task (deciding if a word is abstract or concrete)
nonsemantic – lower or upper letters12 right handed normal subjectsalternating semantic, nonsemantic, and visual
fixationnovelty of the words in the semantic/nonseman-
tic equal
Blocked Design Experiment ResultsReaction times were longer for semantic (873ms)
than nonsemantic (539)Subsequent memory superior following semantic
(85% recognized) than nonsemantic (47%)Regions in left prefrontal cortex and fusiform gyri
demonstrated greater activation during semantic processing.
- BUT do not directly specify the encoding differ-ences that predict whether a specific experience will be later remembered or forgotten
Event Related fMRISingle incidental encoding task
to determine whether trial-by-trial differences in encoding activation predict subsequent memory for experiences even when the process-ing task was held constant.
13 normal, right handed subjects underwent six fMRI scans
each presented with 120 rapidly intermixd trialslater tested on recognition test
high confidence hits, low confidence hits, misses, and fixation
Event Related fMRI ResultsIdentified of regions that demonstrate differential acti-
vation during the encoding of words subsequently re-membered and those subsequently forgottenGreater activation was noted in multiple left prefrontal
regions and left parahippocampal and fusiform gyri
The subsequent memory effect was rather specific: other regions active during word processing relative to fixation failed to demonstrate greater activation dur-ing high confidence hits relative to misses
DiscussionLeft prefrontal and temporal regions showed
significantly greater activation for subsequently remembered items
Remembering verbal items depends on the ex-tent to which left prefrontal and medial temporal re-gions are engaged during the experience.
The role of parahippocampal gyrus in memory encoding extends beyond novelty detection and encompasses more general encoding mecha-nisms
My thoughtsStrengths
Very concise and preciseTwo experimental designs to tackle the ques-
tion effectivelyDiscovering the novel function of temporal re-
gions in verbal memoryfMRI scans
LimitsSmall sample size (12~13)Only focused on verbal memory encoding
Further ResearchParahippocampal gyrus is the principal neo-
cortical input pathway to the hippocampal region, and thus it is suitably situated to play an impor-tant role in memory formation
further investigation of the circuitry us-ing direct inhibition or agonists.
Further research in non-verbal memory tasks
Questions?