Functional imaging of mirror and inverse reading reveals separate coactivated networks for oculomotion and spatial transformations.

Abstract

Echoplanar functional magnetic resonance imaging (fMRI) was used to localize the cortical areas involved in the analysis of spatially transformed letter strings. Significant increases of the blood oxygen level-dependent (BOLD) signal for transformed vs normal reading were observed in the superior parietal lobule (SPL), along the intraparietal sulcus (IPS), in the frontal eye fields (FEF), and in the latero-occipital area LO. The respective contributions of oculomotor and spatial transformation areas to this activation pattern were separated by means of a control condition involving the execution and suppression of eye movements. Areas activated in association with the control of eye movements included the superior parietal lobule and the frontal eye fields. The cooperation of different brain areas was analysed by correlating the time course of task-dependent BOLD signal changes in these areas. This correlation analysis revealed coactivation of occipitotemporal object recognition areas and a spatial transformation area in the intraparietal sulcus during the reading of transformed letter strings. We suggest that cortical systems that are coactivated during complex cognitive tasks can be differentiated by the correlation analysis of BOLD signal time courses in spatially separate brain areas.