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?