Neuronal correlates of encoding and retrieval in episodic memory during a paired-word association learning task: a functional magnetic resonance imaging study

The investigation of memory function using functional magnetic resonance im aging (fMRI)) is an expanding field of research. The aim of this study was to demonstrate brain-activity patterns related to a word-pair association t ask employing a whole-brain EPI sequence. Six right-handed, healthy male vo lunteers (mean age: 27.5 years) took part in the study. fMRI was performed at a field strength of 1.5 Tesla with 26-32 slices parallel to the AC-PC li ne, depending on individual brain size. Distributed brain regions were acti vated in episodic encoding and retrieval with similarities, but also (disti nct) differences in activation patterns. Bilateral prefrontal cortical area s were involved when comparing encoding as well as retrieval to the referen ce condition (nonsense words). Furthermore, activation was observed in cere bellar areas during encoding, and activation in bilateral parietal areas (p recuneus and inferior parietal cortex) was differentially more pronounced d uring retrieval. The activation of left dorsomedial thalamus during retriev al of high imagery-content word-pair associates may point to the role of th is structure in episodic retrieval. The direct cognitive subtraction of enc oding minus retrieval yielded a differentially larger left prefrontal activ ation. There was a differentially higher right prefrontal activation during retrieval than during encoding, underlining the proposed right/left asymme try for episodic memory processes.