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Free keywords:
Hippocampus; Human brain; Magnetic resonance imaging; Memory; Neuroimaging; Parahippocampus
Abstract:
Visual episodic memory encoding was investigated using echoplanar
magnetic resonance imaging at 2.0 x 2.0 mm2 resolution
and 1.0 mm section thickness, which allows for functional
mapping of hippocampal, parahippocampal, and ventral occipital
regions with reduced magnetic susceptibility artifact. The
memory task was based on 54 image pairs each consisting of a
complex visual scene and the face of one of six different
photographers. A second group of subjects viewed the same
set of images without memory instruction as well as a
reversing checkerboard. Apart from visual activation in occipital
cortical areas, episodic memory encoding revealed consistent
activation in the parahippocampal gyrus but not in the
hippocampus proper. This ®nding was most prominently
evidenced in sagittal maps covering the right hippocampal
formation. Mean activated volumes were 432±293 µl and
259±179 µl for intentional memory encoding and non-instructed
viewing, respectively. In contrast, the checkerboard
paradigm elicited pure visual activation without parahippocampal
involvement.
