Deactivation of Extrastriate Cortex in Unimodal Auditory Priming but not in Cross Modal Priming.

Abstract:
Neuroimaging studies have reported that repetition priming is associated with deactivation in extrastriate cortex. However, all previous studies have used visual stimuli. It is therefore unknown whether the observed deactivation is associated specifically with some aspect of visual perceptual processing or with more general aspects of priming. Moreover, cortical areas involved in nonvisual priming are unknown. We studied unimodal and crossmodal priming using an auditory word stem completion task. In the unimodal condition, subjects first heard a list of words. Later, they said aloud the first word that came to mind in response to word stems (first syllables) of studied (priming) and nonstudied (baseline) words. PET images were obtained during stem completion and a fixation task. Auditory priming was associated with deactivation in the extrastriate cortex (BA 19) bilaterally. Additional deactivations were observed in the right angular gyrus, right precuneus and medial prefrontal cortex. In cross-modal priming, the study list was presented visually and subjects completed auditory word stems. Priming was associated with deactivation in left angular gyrus, but not in any of the above areas, and also with activation in medial prefrontal cortex. It appears that cross-modal priming has a distinct cortical mechanism and that extrastriate cortex is associated with unimodal priming in both visual and auditory modalities.