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Abstract:
Detection of hippocampal activity using fMRI during encoding
of novel environmental scenes is likely mediated by stimulus
properties of the comparison condition. The present study
investigates whether the anterior and posterior hippocampus
differentially encode novelty and stimulus configuration during
novel scene encoding. Whole brain fMRI was performed on 33 subjects
while encoding pictures of novel scenes, repeating scenes, and
novel scrambled scenes. Anterior and posterior hippocampal regions
of interest (ROI) were created by averaging hippocampal masks drawn
on each individual's high-resolution anatomy. The effect of
stimulus novelty was tested with a voxel-wise t-test between
encoding of the novel and repeating scenes. Similarly, comparing
novel scene encoding with novel scrambled scene encoding tested
stimulus configuration effects. Positively thresholded voxels
within each ROI were tallied on an individual basis. A three factor
ANOVA (Hemisphere, Anterior/Posterior, and Comparison Task)
resulted in a significant Comparison Task by Anterior/Posterior
interaction. Comparisons of means demonstrate more anterior
hippocampal voxels were active for the stimulus configuration
contrast and more posterior hippocampus voxels active for the
stimulus novelty comparison. Results suggest that both anterior and
posterior hippocampus are involved in encoding novel environmental
scenes. However, these two regions may encode different properties
of the novel scenes, with posterior hippocampus encoding novelty
and anterior hippocampus encoding stimulus configuration.
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