PREFRONTAL CORTEX INVOLVEMENT IN SELECTIVE LETTER GENERATION - A FUNCTIONAL MAGNETIC-RESONANCE-IMAGING STUDY

Cerebral responses to alternating periods of a control task and a sele ctive letter generation paradigm were investigated with functional Mag netic Resonance Imaging (fMRI). Subjects selectively generated letters from four designated sets of six letters from the English language al phabet, with the instruction that they were not to produce letters in alphabetical order either forward or backward, repeat or alternate let ters. Performance during this condition was compared with that of a co ntrol condition in which subjects recited the same letters in alphabet ical order. Analyses revealed significant and extensive foci of activa tion in a number of cerebral regions including mid-dorsolateral fronta l cortex, inferior frontal gyrus, precuneus, supramarginal gyrus, and cerebellum during the selective letter generation condition. These fin dings are discussed with respect to recent positron emission tomograph y (PET) and fMRI studies of verbal working memory and encoding/retriev al in episodic memory.