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Abstract:
Encoding novel pictures has been used as a model task for
observing increased activation in medial temporal lobe structures
in functional neuroimaging studies. In this task, participants are
shown novel pictures and instructed to memorize them (e.g., Stern
et al., 1996). Increased activity in parahippocampal cortex has
been observed consistently for study of novel pictures compared
with study of repeated, familiar pictures (Wagner et al., 1998;
Brewer et al., 1998). In addition, it has been suggested that the
posterior portion of the hippocampus is particularly involved in
this task relative to the anterior portion (Gabrieli et al., 1997).
Here, fMRI data were collected from five volunteers performing the
standard encoding task. Participants were shown 3 blocks of 12
novel pictures (full-color photographs of complex scenes; 3 s
presentation) each alternating with blocks of a familiar picture
shown repeatedly (12 times; 3 s presentation) while instructed to
memorize all pictures. Each participant completed 3 scanning runs
while whole-brain fMRI data were collected using a 1.5 Tesla GE
SIGNA scanner fitted with a local gradient coil (20-22 6mm sagittal
slices, gradient-recalled EPI with TE=40 ms, TR=3.6s). Increased
activity during encoding was observed within the hippocampal
formation, particularly on the right side, in both anterior and
posterior areas. This result indicates that previous failures to
observe increased activity within the hippocampal formation may
have been due to insufficient sensitivity in the neuroimaging
method rather than a lack of involvement of the hippocampal
formation in the encoding of novel memories for this task.
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