Cortical activation evoked by visual mental imagery as measured by functional MRI

One of the major controversies in cognitive neuroscience is whether primary visual cortex and nearby areas are involved in visual mental imagery. In a functional magnetic resonance imaging (fMRI) study we examined the brain activity of 10 healthy subjects under different task conditions: in the perception condition subjects saw complex geometrical shapes and had to decide whether other highlighted stimuli fall inside or outside the figure. In the imagery condition subjects saw only the highlighted stimuli and were instructed to imagine the previously studied geometrical shapes to solve the same task. Although the behavioral data show a distance effect that would be expected based on topographically organized mental images, the functional imaging data do not show increased activity in primary visual cortex in the imagery condition. In occipital cortex a slightly increased activity was found only in visual association cortex (BA, 19), whereas the highest activation was observed in parietal cortex (BA 7 and 40). The results of the study do not support the assumption that primary visual cortex is involved in visual mental imagery, but rather a network of spatial subsystems and higher visual areas appears to be involved