Verbal fluency as a prefrontal activation probe: a validation study using Tc-99m-ECD brain SPET

This study aimed to investigate the feasibility of brain single-photon emis sion tomography (SPET) in the letter and category fluency paradigm of the C ontrolled Oral Word Association (COWA) test in healthy volunteers. Two grou ps each comprising ten right-handed healthy volunteers were injected twice with 370 MBq technetium-99m ethyl cysteinate dimer following a split-dose p aradigm (resting and activation condition). Statistical parametric mapping (SPM96) was used to determine voxelwise significant changes. The letter flu ency and the category fluency activation paradigm had a differential brain activation pattern. The posterior part of the left inferior prefrontal cort ex (LIPC) was activated in both paradigms, with the category fluency task h aving an extra activation in the anterior LIPC. In the category fluency tas k, but not the letter fluency task, an activation in the right inferior pre frontal cortex was found. These findings confirm to a large extent the resu lts of previous functional magnetic resonance imaging and positron emission tomography studies in semantic and phonological activation paradigms. The choice and validity of various methodological characteristics of the experi mental design leading to these results are critically discussed. It is conc luded that brain SPET activation with the letter fluency and category fluen cy paradigm under standard neuropsychological conditions in healthy volunte ers is both technically and practically feasible.