Priming within and across modalities: Exploring the nature of rCBF increases and decreases

Neuroimaging studies suggest that within-modality priming is associated wit h reduced regional cerebral blood how (rCBF) in the extrastriate area, wher eas cross-modality priming is associated with increased rCBF in prefrontal cortex. To characterize the nature of rCBF changes in within- and cross-mod ality priming, we conducted two neuroimaging experiments using positron emi ssion tomography (PET), In experiment 1, rCBF changes in within-modality au ditory priming on a word stem completion task were observed under same- and different-voice conditions. Both conditions were associated with decreased rCBF in extrastriate cortex. In the different-voice condition there were a dditional rCBF changes in the middle temporal gyrus and prefrontal cortex. Results suggest that the extrastriate involvement in within-modality primin g is sensitive to a change in sensory modality of target stimuli between st udy and test, but not to a change in the feature of a stimulus within the s ame modality. In experiment 2, we studied cross-modality priming on a visua l stem completion test after encoding under full- and divided-attention con ditions, Increased rCBF in the anterior prefrontal cortex was observed in t he full- but not in the divided-attention condition. Because explicit retri eval is compromised after encoding under the divided-attention condition, p refrontal involvement in cross-modality priming indicates recruitment of an aspect of explicit retrieval mechanism. The aspect of explicit retrieval t hat is most likely to be involved in cross-modality priming is the familiar ity effect. (C) 2001 Academic Press.