SUCCESSFUL VERBAL ENCODING INTO EPISODIC MEMORY ENGAGES THE POSTERIORHIPPOCAMPUS - A PARAMETRICALLY ANALYZED FUNCTIONAL MAGNETIC-RESONANCE-IMAGING STUDY

The medial temporal lobe (MTL) is essential for episodic memory encodi ng, as evidenced by memory deficits in patients with MTL damage. Howev er, previous functional neuroimaging studies have either failed to sho w MTL activation during encoding or they did not differentiate between two MTL related processes: novelty assessment and episodic memory enc oding. Furthermore, there is evidence that the MTL can be subdivided i nto subcomponents serving different memory processes, but the extent o f this functional subdivision remains unknown. The aim of the present functional magnetic resonance imaging (fMRI) study was to investigate the role of the MTL in episodic encoding and to determine whether this function might be restricted to anatomical subdivisions of the MTL. T hirteen healthy volunteers performed a word list learning paradigm wit h free recall after distraction. Functional images acquired during enc oding were analyzed separately for each participant by a voxel-wise co rrelation (Kendall's tau) between the time series of the T2-signal in tensity and the number of subsequently recalled words encoded during e ach particular scan. Of the 13 participants, 11 showed voxel clusters with statistically significant, positive correlations in the posterior part of the hippocampus. Across participants, an ANOVA on the number of voxels with significant, positive correlations within individually defined volumes of interest confirmed a statistically significant diff erence in activation for anterior versus posterior regions of the hipp ocampus. However, no differences between left and right hippocampal ac tivation were revealed. Thus, these findings demonstrate that successf ul encoding into episodic memory engages neural circuits in the poster ior part of the hippocampus.