Functional asymmetry of human prefrontal cortex in verbal and non-verbal episodic memory as revealed by fMRI

Functional neuroimaging studies have demonstrated preferential involvement of bilateral prefrontal cortex during episodic memory encoding and retrieva l. The aim of the present study is to address the question whether left pre frontal model for encoding holds when highly non-verbal material is used, a nd which region of the brain is critically related to successful retrieval. To do this, seven normal subjects were investigated using functional magne tic resonance imaging (fMRI) during encoding and retrieval of word and chec kerboard pattern. Our results revealed that word encoding activated the lef t prefrontal cortices and right cerebellum, whereas pattern encoding activa ted the bilateral middle frontal gyrus, superior parietal lobule, premotor area, and occipital visual cortex. Word-specific activation was found in th e ventral prefrontal cortices, and pattern-specific activation located in t he right dorsal prefrontal cortex. Conjunction analysis during encoding of word and pattern showed that activity in the left dorsal prefrontal cortex and the right cerebellum might relate to common neural network for encoding regardless of the type of material. Finally, the present study demonstrate s strong association between the left ventral prefrontal cortex and retriev al success for word. The evidence, that both encoding and retrieval of word s activated the left ventral prefrontal cortex, indicates that this area is involved in active and strategic operation of the mnemonic representation. A lack of the right prefrontal activation during retrieval was interpreted as that activity in this region might relate to retrieval effort rather th an success. (C) 2000 Elsevier Science B.V. All rights reserved.