title: Decoupled visually-guided reaching in optic ataxia: differences in motor control between canonical and non-canonical orientations in space.
abstract: Guiding a limb often involves situations in which the spatial location of the target for gaze and limb movement are not congruent (i.e. have been decoupled). Such decoupled situations involve both the implementation of a cognitive rule (i.e. strategic control) and the online monitoring of the limb position relative to gaze and target (i.e. sensorimotor recalibration). To further understand the neural mechanisms underlying these different types of visuomotor control, we tested patient IG who has bilateral caudal superior parietal lobule (SPL) damage resulting in optic ataxia (OA), and compared her performance with six age-matched controls on a series of center-out reaching tasks. The tasks comprised 1) directing a cursor that had been rotated (180° or 90°) within the same spatial plane as the visual display, or 2) moving the hand along a different spatial plane than the visual display (horizontal or para-sagittal). Importantly, all conditions were performed towards visual targets located along either the horizontal axis (left and right; which can be guided from strategic control) or the diagonal axes (top-left and top-right; which require on-line trajectory elaboration and updating by sensorimotor recalibration). The bilateral OA patient performed much better in decoupled visuomotor control towards the horizontal targets, a canonical situation in which well-categorized allocentric cues could be utilized (i.e. guiding cursor direction perpendicular to computer monitor border). Relative to neurologically intact adults, IG's performance suffered towards diagonal targets, a non-canonical situation in which only less-categorized allocentric cues were available (i.e. guiding cursor direction at an off-axis angle to computer monitor border), and she was therefore required to rely on sensorimotor recalibration of her decoupled limb. We propose that an intact caudal SPL is crucial for any decoupled visuomotor control, particularly when relying on the realignment between vision and proprioception without reliable allocentric cues towards non-canonical orientations in space.
authors.affiliation: School of Kinesiology and Health Science, Centre for Vision Research, York University, Toronto, Ontario, Canada.
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Granek
authors.affiliation: Impact - Centre de Recherche en Neurosciences de Lyon, Inserm U 1028, CNRS UMR 5092, Bron, France.
authors.forename: Laure
authors.initials: L
authors.lastname: Pisella
authors.affiliation: School of Kinesiology and Health Science, Centre for Vision Research, York University, Toronto, Ontario, Canada.
authors.forename: John
authors.initials: J
authors.lastname: Stemberger
authors.affiliation: Impact - Centre de Recherche en Neurosciences de Lyon, Inserm U 1028, CNRS UMR 5092, Bron, France ; Biologie Humaine, Université Lyon, Lyon, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Vighetto
authors.affiliation: Impact - Centre de Recherche en Neurosciences de Lyon, Inserm U 1028, CNRS UMR 5092, Bron, France ; Biologie Humaine, Université Lyon, Lyon, France ; Mouvement et Handicap, Hospices Civils de Lyon, Hôpital Neurologique Pierre Wertheimer, Bron, France.
authors.forename: Yves
authors.initials: Y
authors.lastname: Rossetti
authors.affiliation: School of Kinesiology and Health Science, Centre for Vision Research, York University, Toronto, Ontario, Canada.
authors.forename: Lauren E
authors.initials: LE
authors.lastname: Sergio
mesh_terms: D000328:Adult; D001259:Ataxia / Q000503:physiopathology* / Q000523:psychology*; D023381:Endpoint Determination; D005133:Eye Movements / Q000502:physiology; D005260:Female; D006225:Hand / Q000502:physiology; D006801:Humans; D008297:Male; D009949:Orientation / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology*; D013028:Space Perception / Q000502:physiology*; D013997:Time Factors; D014796:Visual Perception / Q000502:physiology*