Temporal sorting of neural components underlying phonological processing.

Event-related haemodynamic responses (EHRs) were recorded in subjects performing phonological tasks to test whether distinguishable temporal involvement of corresponding neural components would show through. A sequence of activation leading from primary auditory cortices to premotor regions emerged in the fast repetition and the phoneme monitoring tasks used. EHRs peaked significantly earlier in Wernicke's area (phonological decoding) than in Broca's area, the left supramarginal gyrus and the precentral gyrus (phonological rehearsal). Moreover, the sensitivity of within cluster temporal gradients to the nature of the tasks indicated either sensory to association cortex synchronization for fast repetition or delayed analysis for phoneme monitoring. These results are consistent with previous findings on working memory and show that fMRI permits temporal tracking of cognitive activations.