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Abstract:
Abstract: Both inferior and dorsal regions along inferior
frontal gyrus (IFG) play a role in episodic encoding of words
(Buckner et al., 1999 Nature Neurosci.), but their individual
contributions to this domain have remained elusive, even though
evidence for dissociations between regions has been reported
(Buckner et al., 1995 J. Neurophy.). Using fMRI, regional
activation during multiple encoding conditions was examined to
determine whether distinct regions of frontal cortex make separate
contributions to episodic memory formation. 18 younger adults
performed three encoding tasks: shallow incidental encoding, deep
incidental encoding, and intentional encoding. During each task
subjects viewed words (~2.5 sec apart) separated by extended
fixation blocks. Importantly, the deep and shallow encoding tasks
were both constructed to require similar amounts of processing time
(Demb, et al. 1995). Results indicated a clear dissociation between
separate frontal regions. All tasks activated the dorsal portion of
IFG (BA 44/6), consistent with a highly general role of this region
in the representation of verbal stimuli, perhaps based on
phonology. The inferior portion of IFG (BA 44/45/47) was most
active during meaning-based processing (deep incidental) and
minimally active during the shallow incidental encoding task.
Memory performance was significantly better following deep over
shallow processing suggesting inferior (and not dorsal) IFG is
selectively involved in verbal episodic memory formation.
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