Neural correlates of semantic matching in indirect priming

Abstract

Electrophysiological and functional neuroimaging studies have demonstrated the role of a left temporo-parietal brain network in prospective processing during direct priming (“body” – “hand”) using a short stimulus onset asynchrony (SOA). In contrast, indirect priming (“lion” – “stripes” related through “tiger”) has been related to the activation of right hemisphere regions such as the supramarginal and middle frontal gyri and the insula involved in automatic semantic processing. Postlexical retrospective strategies like semantic matching, compound cue or episodic retrieval have been largely neglected even though there is consistent evidence of their contribution to direct and indirect priming. The present study was designed to map the brain regions participating in semantic priming based on postlexical retrospective semantic matching. 16 right-handed Spanish speakers (ages 20–40, 50 % male) were given a visual lexical decision task in a 1.5 T scanner with a TR of 3.5 s to obtain BOLD activations. In order to reduce the effects of automatic spreading activation on priming we used a long SOA (800 ms). To minimize the effects of expectancy, we increased the related-unrelated ratio to 1:2 (20 related, 40 unrelated, 20 pseudowords) and employed an indirect priming paradigm with weakly associated targets to enhance the effects of semantic matching. Each 3500 ms trial consisted on a fixation screen for 1000 ms followed by a 100 ms black screen, then the prime word for 600 ms, another black screen for 200 ms, the target word/pseudoword for 600 ms and finally a response screen for 1000 ms. Response time was longer for pseudowords compared to related and unrelated targets. An increased activity was found in lIFG for related pairs and pseudowords, whereas a large cluster of activation was found in left fusiform gyrus for unrelated pairs. Right insula was also activated for unrelated and pseudoword conditions. Furthermore, all conditions showed a decreased activity in left precuneus/parieto-occipital sulcus. These data addressed the role of frontal, temporal, parietal and insular regions in retrospective semantic matching with a differential pattern according to the lexical retrieval, selection and inhibition processes required to make a lexical decision.