Functional MRI with reduced susceptibility artifact: high-resolution mapping of episodic memory encoding

Visual episodic memory encoding was investigated using echo-planar magnetic resonance imaging at 2.0 x 2.0 mm(2) resolution and 1.0 mm section thickne ss, which allows for functional mapping of hippocampal, parahippocampal, an d ventral occipital regions with reduced magnetic susceptibility artifact. The memory task was based on 54 image pairs each consisting of a complex vi sual scene and the face of one of six different photographers. A second gro up 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 finding was most prominently evidenced in sagittal maps covering the right hippoca mpal formation. Mean activated volumes were 432+/-293 mul and 259+/-179 mul for intentional memory encoding and non-instructed viewing, respectively. In contrast, the checkerboard paradigm elicited pure visual activation with out parahippocampal involvement. NeuroReport 12:1415-1420 (C) 2001 Lippinco tt Williams & Wilkins.