Spatial coding of visual and somatic sensory information in body-centred coordinates

Because sensory systems use different spatial coordinate frames, cross-moda l sensory integration and sensory-motor coordinate transformations must occ ur to build integrated spatial representations. Multimodal neurons using no n-retinal body-centred reference frames are found in the posterior parietal and frontal cortices of monkeys. We used functional magnetic resonance ima ging to reveal regions of the human brain using body-centred coordinates to code the spatial position of both visual and somatic sensory stimuli. Part icipants determined whether a visible vertical bar (visual modality) or a l ocation touched by the right index finger (somatic sensory modality) lay to the left or to the right of their body mid-sagittal plane. This task was c ompared to a spatial control task having the same stimuli and motor respons es and comparable difficulty, but not requiring body-centred coding of stim ulus position. In both sensory modalities, the body-centred coding task act ivated a bilateral fronto-parietal network, though more extensively in the right hemisphere, to include posterior parietal regions around the intrapar ietal sulcus and frontal regions around the precentral and superior frontal sulci, the inferior frontal gyrus and the superior frontal gyrus on the me dial wall. The occipito-temporal junction and other extrastriate regions ex hibited bilateral activation enhancement related to body-centred coding whe n driven by visual stimuli. We conclude that posterior parietal and frontal regions of humans, as in monkeys, appear to provide multimodal integrated spatial representations in body-centred coordinates, and these data furnish the first indication of such processing networks in the human brain.