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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