Brain activation during automatic and controlled processing of semantic relations: a priming experiment using lexical-decision.

Semantic relations may be studied using the experimental technique known as semantic priming, in which a word 'primes' the processing of a related target (e.g. lion-tiger), following a short delay. Priming may be automatic or, with longer delays, under more controlled processing. This study used functional magnetic resonance imaging (fMRI) to examine the cerebral activation during two lexical-decision semantic priming experiments, with a short and long delay, representing automatic and controlled processing, respectively. A further two un-primed lexical-decision tasks were performed to distinguish cerebral activation specific to semantic priming itself from those utilised during lexical-decision processes. Distinct regions of anterior cingulate cortex (ACC) were critical to automatic and controlled semantic priming, whilst the putamen and hippocampal complex responded differently to unrelated and semantically related prime-target pairs. Lexical-decision alone revealed activation in posterior temporal cortex especially on the left, in agreement with previous neuroimaging studies. The results provide a plausible neural substrate for common semantic relations independent of task demands and further emphasise the regional functional specialisation of the ACC.