Functional specialization for semantic and phonological processing in the left inferior prefrontal cortex

Neuroimaging and neuropsychological studies have implicated left inferior p refrontal cortex (LIPC) in both semantic and phonological processing. In th is study, functional magnetic resonance imaging was used to examine whether separate LIPC regions participate in each of these types of processing. Pe rformance of a semantic decision task resulted in extensive LIPC activation compared to a perceptual control task. Phonological processing of words an d pseudowords in a syllable-counting task resulted in activation of the dor sal aspect of the left inferior frontal gyrus near the inferior frontal sul cus (BA44/45) compared to a perceptual control task, with greater activatio n for nonwords compared to words. In a direct comparison of semantic and ph onological tasks, semantic processing preferentially activated the ventral aspect of the left inferior frontal gyrus (BA 47/45). A review of the liter ature demonstrated a similar distinction between left prefrontal regions in volved in semantic processing and phonological/lexical processing. The resu lts suggest that a distinct region in the left inferior frontal cortex is i nvolved in semantic processing, whereas other regions may subserve phonolog ical processes engaged during both semantic and phonological tasks. (C) 199 9 Academic Press.