THE ROLE OF THE LEFT PREFRONTAL CORTEX IN VERBAL PROCESSING - SEMANTIC PROCESSING OR WILLED ACTION

THIS study was designed to test the various proposed explanations (sem antic processing, willed action, production of a spoken response) for the unilateral activation of the left prefrontal cortex noted in PET s tudies of verbal processing. Twenty subjects underwent O-15-water PET scans while undertaking a lexical task (detecting the letter 'a' in vi sually presented words) and a semantic task (categorizing nouns into l iving/non-living). The semantic task resulted in a significant unilate ral left dorsolateral prefrontal activation. This finding suggests tha t the left inferior prefrontal cortex is the anatomical region involve d in 'working with meaning', and that the activation does not reflect willed action, is not task-specific and is not attributable to the req uirements of a spoken response.