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 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 finding was most prominently evidenced in sagittal maps covering the right hippocampal 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 without parahippocampal involvement. NeuroReport 12:1415-1420 (C) 2001 Lippincott Williams & Wilkins.