An event-related fMRI investigation of phonological versus semantic short-term memory

Studies with normal and brain damaged subjects have indicated that there are semantic as well as phonological contributions to verbal short-term memory. An event-related functional MRI study was carried out to determine if different brain regions would be activated during the delay period in a phonological vs. a semantic retention task. A recognition probe procedure was used in which memory load and task (i.e. rhyme judgment vs. synonym judgment) were manipulated. A left inferior parietal region overlapping the supramarginal gyrus was more activated in the phonological than the semantic task. A large left inferior and mid-frontal region and another left parietal region showed a load effect that was common to the phonological and semantic tasks. No region showed significantly greater activation in the semantic than the phonological task, though there was a trend towards a more anterior localization of the frontal load effect in the semantic task compared to the phonological task.