Brain Activity Underlying Lexical Access: An Event-related Functional Magnetic Imaging Study

Abstract:
Abstract: Word recognition depends on activation of word or word-like representations. To identify the brain areas involved in such lexical processing, event-related fMRI at 1.5 Tesla was used to measure left hemisphere activation in 20 individuals during a visual lexical decision task. A factorial design was employed, with lexical status (word-nonword) and orthographic neighborhood size (number of lexical neighbors) as factors. Deconvolution analysis on the time series data revealed that the hemodynamic response differed across the levels of the two factors at time lags of 4, 6, and 8 seconds after stimulus onset. The lexical effect was stronger than the orthographic neighborhood size effect, which was minimal at all time points. Across all time lags, compared to nonwords, words produced greater activation in posterior brain regions including the angular gyrus and posterior cingulate gyrus, as well as in prefrontal cortex in the superior and inferior frontal sulci. Nonwords activated the ventral premotor area, pars opercularis, supramarginal gyrus, and anterior segments of the superior temporal gyrus more than did words. These data support a role for the angular gyrus and posterior cingulate in semantic processing and suggest that the degree of semantic information associated with a stimulus predicts the location of brain activity within the overall lexical processing network.