Spatial orienting by left hemisphere language areas: a relict from the past?

During evolution, the human brain developed remarkable functional differences between left and right hemispheres. Due to this lateralization, disorders of spatial orienting occur predominantly after right brain damage and disorders of language after left brain damage. In contrast to this general pattern, few individuals show disturbed spatial orienting (spatial neglect) after left brain damage. Using a voxel-based lesion analysis approach, we found that neglect after acute left brain damage is represented in areas typically serving language functions, namely the superior and middle temporal gyri, inferior parietal lobule and insula. Since all except one of these patients also suffered from aphasia, we conclude that lateralization is not just reversed but that both functions (language and spatial orienting) rather are represented in the same left hemisphere regions. We speculate that a representation of spatial orienting in left hemisphere language areas might be a phylogenetic relict in humans, though this representation stays subdominant in the vast majority of individuals.