Neural substrates of orthographic lexical access as demonstrated by functional brain imaging

Objective: To delineate regions involved in visual word recognition. Background: The processes and regions involved in visual word recognition have been somewhat controversial for over 100 years. Methods: This study used regional cerebral blood flow as assessed by functional magnetic resonance imaging to study normal subjects (N = 9) on an individual within-subject basis while they were actively engaged on-line in a visual lexical decision task. Standard analysis techniques were used for identifying regions of activation. Results: Across subjects, the task activated a number of regions, including the occipital pole, lateral and basal occipitotemporal (including lingual and fusiform) regions, superior and middle temporal gyri, and supramarginal and angular gyri. Typically, these regions were activated bilaterally; when activation was unilateral, it was on the left. Some of the areas activated (e.g., inferior parietal regions) have not been previously reported to be involved in such types of processing by activation studies but have been implicated in lesion studies. Conclusions: These results broaden the areas known to be involved in visual word recognition. The bilateral activation associated with visual word recognition is in some respects analogous to the 'what' system in visual recognition described in subhuman primates. In addition, the study raises several methodologic issues. The within-subject analysis showed variability in the specific regions activated when subsequently comparing across individuals, raising implications for future functional imaging studies.