title: Spatial attention and interhemispheric visuomotor integration in the absence of the corpus callosum.
abstract: In the lateralized simple reaction time (SRT) task with unimanual responses (Poffenberger paradigm), reaction times (RTs) are faster with ipsilateral (uncrossed) than with contralateral (crossed) response hand-target hemifield combinations. The difference between crossed and uncrossed responses (CUD) has typically been interpreted to reflect callosal transfer time. Indeed, acallosal subjects and split-brain subjects have longer CUDs than control subjects. However, a few recent studies have demonstrated that, contrary to classical findings, the CUD is also affected by non-anatomical factors. Here we show that the CUD is also affected by non-anatomical factors in patients with agenesis of the corpus callosum and complete commissurotomy where interhemispheric transfer must be subcallosal. We tested acallosal subject M.M. and split brain patient A.A. on a lateralized SRT task with their arms alternately uncrossed (natural arms position) or crossed (unnatural arms position) across blocks of trials. The results revealed a significant effect of arms crossing on the size and direction of the CUD as previously found in normal subjects [Mooshagian, E., Iacoboni, M., & Zaidel, E. (2008). The role of task history in simple reaction time to lateralized light flashes. Neuropsychologia, 46(2), 659-664]. This suggests that non-anatomical factors that modulate interhemispheric visuomotor integration may occur in absence of the corpus callosum. Anterior commissure and interhemispheric cortico-subcortical pathways are likely implicated in these effects.
authors.affiliation: Department of Psychology, University of California, Los Angeles, Los Angeles, CA 90095, United States. mooshage@ninds.nih.gov
authors.forename: Eric
authors.initials: E
authors.lastname: Mooshagian
authors.forename: Marco
authors.initials: M
authors.lastname: Iacoboni
authors.forename: Eran
authors.initials: E
authors.lastname: Zaidel
mesh_terms: D000328:Adult; D061085:Agenesis of Corpus Callosum; D001288:Attention; D003337:Corpus Callosum / Q000503:physiopathology* / Q000601:surgery; D007839:Functional Laterality; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009039:Motion Perception; D009434:Neural Pathways; D011597:Psychomotor Performance; D011930:Reaction Time; D013028:Space Perception; D014796:Visual Perception