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Abstract:
Source memory depends on associative learning mechanisms that
bind distinct event features into an integrated memory trace such
that the features can be later consciously remembered. To explore
the neural substrates of associative encoding, event-related fMRI
indexed whether encoding activation predicts later source
recollection when item memory is held constant. During scanning,
subjects were presented individual adjectives. For "scene" encoding
trials, subjects imagined a visual scene that corresponded to each
adjective (e.g., imagining a garbage dump when presented "dirty").
Prior data suggest that scene imagery elicits activation in
posterior parahippocampal gyrus. For "read" encoding trials,
subjects silently read each adjective backwards. Approximately 18
hrs after scanning, memory for the studied adjectives was assessed
via yes-no recognition. For recognized items (hits), subjects
further indicated the encoding source (scene or read). Results
revealed greater posterior parahippocampal, hippocampal, and left
prefrontal activation during "scene" relative to "read" encoding.
When subsequent item memory was held constant following "scene"
encoding, comparison of source hits to source misses revealed
greater MTL and PFC activation. These effects were selective as
they were not observed in the "read" encoding condition.
Collectively, these findings indicate that PFC and MTL regions
subserve associative encoding processes that support subsequent
recollection of semantic and visuospatial source knowledge.
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