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Abstract:
Neuroimaging studies have identified brain regions in medial
temporal and frontal cortical areas that support memory encoding
and retrieval. However, previous studies have usually studied each
of these processes separately. In order to directly compare the
activity associated with encoding, recognition, and source memory
retrieval, we designed a protocol combining study trials and both
recognition and recency memory judgments in an event-related
design. Participants performed five fMRI scanning runs (1.5T
Siemens Vision, 24x6mm axial slices, TR=2.0s) each containing 79
abstract visual stimuli to be studied, 36
two-alternative-forced-choice test trials and 40 fixation-point
trials. Two types of memory test were used: recognition ("indicate
which picture you have seen before"; 18 questions) and recency
("indicate which picture you have seen most recently"; 18
questions). All trial types were displayed for 3s. Memory test
trials were interspersed among study trials such that recognition
was tested for items seen 1-25 trials previously. Recency
discrimination involved two stimuli each seen from 1-25 trials
previously. Direct comparison of encoding and retrieval showed
greater activation during encoding, particularly in the anterior
and posterior MTL, occipital-parietal cortex and lateral temporal
cortical areas. Compared with recognition, source memory retrieval
elicited stronger activity in the right dorsolateral prefrontal
cortex, bilateral fronto-polar cortex, and both dorsal and ventral
visual processing areas.
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