Building memories remembering and forgetting of verbal experiences by gjjur4356

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									     Building memories
remembering and forgetting of
    verbal experiences as
  predicted by brain activity
    Anthony D. Wagner, Daniel L.
   Schacter, Michael Rotte, Wilma
   Koutstaal, Anat Maril, Anders M.
   Dale, Bruce R. Rosen, Randy L.
               Buckner
         By: Andrea Ching
             Background
 What is memory encoding?
   Memory encoding refers to the processes
   by which an experience is transformed into
   an enduring memory trace.
             Background
 Memorability of an event is influenced
  by the cognitive operations during the
  initial encoding of the event.
 Semantic processing>Nonsemantic
  processing
             Background
 Left pre-frontal cortex involved in verbal
  encoding
 Left pre-frontal cortex activation greater
  in semantic relative to non-semantic
  encoding.
             Background
 Medial temporal regions
   Lesion studies
 No medial temporal activation
   Neuroimaging studies
 Parahippocampal gyrus
   Novel stimuli > familiar stimuli
    Method-First Experiment
 Twelve normal, right handed subjects
 Seven men, five women
 Aged 18-29 years
    Method-First Experiment
 Blocked design experiment
  Trials from each encoding condition are
   presented sequentially inseparable from
   each other during the scan
 Comparison between activation during
  semantic vs non-semantic processing
  task
    Method-First Experiment
 Alternating task-blocks
  Semantic processing
  Non-semantic processing
  Visual fixation
 Novelty of the words are equivalent in
  semantic and non-semantic blocks.
    Method-First Experiment
 During semantic and nonsemantic blocks, 20
  words were visually presented: 10 abstract
  and 10 concrete nouns; half in uppercase and
  half in lowercase letters.
 Each word was presented for 1 s followed by
  1 s of fixation between words.
 Memory was assessed using a yes-no
  recognition procedure after 20 to 40 minutes
    Results-First Experiment
 Reaction times were longer for semantic
  decisions
 Subsequent memory was superior
  following semantic (85% recognized)
  than following non-semantic
  processing(47% recognized).
Greater Activation during
  Semantic Processing
  Method-Second Experiment
 Thirteen normal, right-handed subjects
 Six men and seven women
 Aged 18-35 years
  Method-Second Experiment
 Event-related fMRI was used while
  participants performed a single incidental
  encoding task.
 Word and fixation events presented in a
  continuous series of 120 intermixed trials.
 Semantic decision during word trials(abstract
  or concrete).
 Recognition test (High or low confidence).
  Method-Second Experiment
 fMRI data analysis: four encoding trial
  types
  High confidence hits
  Low confidence hits
  Misses
  Fixation
  Results-Second Experiment
 Word processing relative to fixation
  resulted in greater activation
 High confidence hits to misses
  Multiple left prefrontal regions
  Left parahippocampal gyrus
  Fusiform gyrus
                 Discussion
 Magnitude of activation is greater in
  remembered events
   Subsequently remembered events are processed
    longer during learning
 Reaction times for high confidence hits and
  miss trials were matched
   Greater activation in left prefrontal and temporal
    regions in subsequently remembered items
              Discussion
 Left parahippocampal gyrus is more
  active in later remembered events even
  though both were equally novel
 Extends beyond novelty detection
  more general encoding mechanism
 Principal neocortical input to
  hippocampal region
  important role in memory formation
                Conclusion
 Verbal experience may be more memorable
  when semantic and phonological attributes
  are processed via the left prefrontal regions.
 Organization in working memory serves as
  input to the parahippocampal gyrus and the
  medial temporal memory system.
 Left prefrontal and temporal processes will
  tend to produce more memorable verbal
  events.
              Strengths
 Limited confounds
  Reaction times
 Were able to identify many brain
  regions that were involved in
  remembering
             Limitations
 Small sample size
         Future Research
 Instead of words they could use
  pictures
 Age, sex differences
            References
Wagner AD, Schacter DL, Rotte M,
   Koutstaal W, Maril A, Dale AM,
   Rosen BR, Buckner RL (1998)
   Building memories: remembering
   and forgetting of verbal
   experiences as predicted by brain
   activity. Science, 281(5350), 1188
   –1191.

								
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