Geographic mental imagery recruits a network of early visual areas

Using functional MRI (fMRI), we studied brain signal changes in 17 volunteers that accompanied performance of a visual mental imagery task. Subjects were required to name states within the continental US, in clockwise or counter-clockwise order based on location, and starting from a target state. Signal increases were compared to a rest control state and to an auditorally-cued verbal naming task. Group analyses of the geographic imagery condition showed extensive bilateral recruitment of cuneus, posterior and anterior (R>L) cingulate. A predominantly right-sided focus was observed in the right lateral geniculate. When contrasted with the verbal task, geographic imagery showed greater fMRI signal near the occipito-parietal junction, including BA 18 and 19 and 39. The activity in the anterior cingulate did not appear in this contrast, however. Taken in context, these data support the hypothesis that mental imagery tasks activate brain regions that would otherwise be involved in computations on sensory information in order to perform comparable tasks. The geographic imagery condition, in particular, requires re-representation of topologic features onto early visual areas, which are then interrogated for spatial relations. Striking in their absence, were activation foci in hippocampal or parahippocampal regions that might be engaged in memory components. This suggests that subjects performed the task based primarily on visual analyses.