A Parametrically Analyzed Functional MRI Study of Verbal Encoding into Episodic Memory

Abstract:
The aim of the present functional MRI study was to investigate the role of the medial temporal lobe in verbal encoding into episodic memory. Thirteen young healthy volunteers performed a single-trial word-list learning paradigm with free recall following distraction. Functional images acquired during encoding were analyzed separately for each participant by a voxel-wise correlation (Kendall's-tau) between the time series of the T2*-signal intensity and the number of subsequently recalled words encoded during each particular scan. Eleven of 13 participants showed voxel clusters with significant, positive correlations in the posterior part of the hippocampus proper. Across participants, an ANOVA on the number of voxels with significant, positive correlations within individually defined volumes of interest confirmed a statistically significant difference in activation for anterior versus posterior regions of the hippocampus. However, no differences between left and right hippocampal activation were revealed. Thus, these findings demonstrate that successful encoding into episodic memory engages neural circuits in the posterior part of the hippocampus proper.