title: Interhemispheric visuo-motor integration in humans: the role of the superior parietal cortex.
abstract: We used event-related functional magnetic resonance imaging (fMRI) to investigate the neural correlates of basic interhemispheric visuo-motor integration. In a simple reaction time task, subjects responded to lateralized left and right light flashes with unimanual left and right hand responses. Typically, reaction times are faster for uncrossed responses (that is, visual stimulus and response hand on the same side) than for crossed responses (that is, visual stimulus and response hand on opposite sides). The chronometric difference between crossed and uncrossed responses is called crossed-uncrossed difference (CUD) and it is typically taken to represent a behavioral estimate of interhemispheric transfer time. The fMRI results obtained in normal right-handers show that the crossed conditions yielded greater activity, compared to the uncrossed conditions, in bilateral prefrontal, bilateral dorsal premotor, and right superior parietal areas. These results suggest that multiple transfers between the hemispheres occur in parallel at the functional levels of sensory-motor integration (posterior parietal), decision-making (prefrontal) and preparation of motor response (premotor). To test the behavioral significance of these multiple transfers, we correlated the individual CUDs with the difference in signal intensity between crossed and uncrossed responses in the prefrontal, dorsal premotor, and right superior parietal activated areas. The analyses demonstrated a strong correlation between the CUD and signal intensity difference between crossed and uncrossed responses in the right superior parietal cortex. These data suggest a critical role of the superior parietal cortex in interhemispheric visuo-motor integration.
authors.affiliation: Department of Psychiatry and Biobehavioral Sciences, Ahmanson Lovelace Brain Mapping Center, Neuropsychiatric and Brain Research Institute, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095-7085, USA. iacoboni@loni.ucla.edu
authors.forename: Marco
authors.initials: M
authors.lastname: Iacoboni
authors.forename: Eran
authors.initials: E
authors.lastname: Zaidel
mesh_terms: D000328:Adult; D002540:Cerebral Cortex / Q000502:physiology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D010296:Parietal Lobe / Q000502:physiology*; D010775:Photic Stimulation; D017397:Prefrontal Cortex / Q000502:physiology; D011597:Psychomotor Performance / Q000502:physiology*; D011930:Reaction Time; D012016:Reference Values; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology