Differential activity in left inferior frontal gyrus for pseudo and real words: an event-related functional MRI study on auditory lexical decision

Abstract

Objective To study lexical processing of pseudo words and real words by using a fast event-related functional MRI (ER-fMRI) design. Methods Participants did an auditory lexical decision task on a list of pseudo-randomly intennixed real and pseudo Chinese two-character (or two-syllable) words. Pseudo words were constructed by recombining constituent characters of the real words to control for sublexical codes properties. Results The behavioral performance of fourteen participants indicated that response to pseudowords was significantly slower and less accurate than to real words ( mean error rate: 9. 9% versus. 3.9%, mean reaction time: 1618 ms versus 1143 ms ) . Processing of pseudo words and real words activated a highly comparable network of brain regions, including bilateral inferior frontal gyrus, superior, middle temporal gyrus, calcarine and lingual gyrus, and left supramarginal gyrus. Mirroring a behavioral lexical effect, left inferior frontal gyrus (IFG) was significantly more activated for pseudo words than for real words. Conclusion The results indicate that the processing of left inferior frontal gyrus in judging pseudo words and real words is not related to grapheme-to-phoneme conversion, but rather to making positive versus negative responses in decision making.