EFFECTS OF PREFRONTAL LESIONS ON LEXICAL PROCESSING AND REPETITION PRIMING - AN ERP STUDY

The role of left prefrontal cortex in lexical-semantic processing rema ins a matter of some debate. Functional neuroimaging experiments have reported blood flow changes in left inferior prefrontal cortex (LIPC) during tasks that involve word retrieval and semantic processing. Some of these studies have also implicated LIPC in repetition priming. To determine the necessity of prefrontal cortex for these types of memory and to elucidate their time-course, behavioral and event-related pote ntial (ERP) correlates of lexical processing and repetition priming we re examined in 11 stroke patients with lesions centered in dorsolatera l prefrontal cortex (areas 9 and 46). Damage extended inferiorly and p osteriorly to areas 6, 8, 44, and 45 in some subjects, so patients wer e subdivided into anterior and posterior frontal subgroups. Visually p resented words and pronounceable non-words were repeated after one of three delays. Subjects categorized stimuli as either words or non-word s in a lexical decision task. Controls showed significant word priming at all three delays. Old words elicited more positive-going potential s than new words, beginning at 300 ms and lasting until 500-700 ms. Th is ERP repetition effect was reduced, but not eliminated, by both ante rior and posterior frontal lesions. However, behavioral priming was in tact in the patients, suggesting that prefrontal cortex may modulate t he neural generators in posterior cortical regions that are critical f or priming. Left posterior frontal lesions resulted in impaired perfor mance in the lexical decision task and a reduction in the amplitude of the late positive component (LPC). These latter findings suggest that left posterior prefrontal cortex is important for the categorization and selection processes required by lexical-semantic tasks. (C) 1998 E lsevier Science B.V. All rights reserved.