An oculomotor and computational study of a patient with diagonistic dyspraxia.
Diagonistic dyspraxia (DD) is a behavioural disorder encountered in split-brain subjects in which the left arm acts against the subject's will, deliberately counteracting what the right arm does. We report here an oculomotor and computational study of a patient with a long lasting form of DD. A first series of oculomotor paradigms revealed marked and unprecedented saccade impairments. We used a computational model in order to provide information about the impaired decision-making process: the analysis of saccade latencies revealed that variations of decision times were explained by adjustments of response criterion. This result and paradoxical impairments observed in additional oculomotor paradigms allowed to propose that this adjustment of the criterion level resulted from the co-existence of counteracting oculomotor programs, consistent with the existence of antagonist programs in homotopic cortical areas. In the intact brain, trans-hemispheric inhibition would allow suppression of these counter programs. Depending on the topography of the disconnected areas, various motor and/or behavioural impairments would arise in split-brain subjects. In motor systems, such conflict would result in increased criteria for desired movement execution (oculomotor system) or in simultaneous execution of counteracting movements (skeletal motor system). At higher cognitive levels, it may result in conflict of intentions.
Pouget
Pierre
P
INSERM U975, Movement Disorders and Basal Ganglia, Hôpital de la Salpêtrière, 47 boulevard de l’Hôpital, Paris, France.
Pradat-Diehl
Pascale
P
Rivaud-Péchoux
Sophie
S
Wattiez
Nicolas
N
Gaymard
Bertrand
B
D000328:Adult; D055964:Alien Limb Phenomenon / Q000209:etiology / Q000473:pathology / Q000503:physiopathology*; D001925:Brain Damage, Chronic / Q000150:complications* / Q000473:pathology / Q000503:physiopathology; D003337:Corpus Callosum / Q000473:pathology*; D003657:Decision Making; D007839:Functional Laterality; D006801:Humans; D008297:Male; D008959:Models, Neurological; D009069:Movement Disorders / Q000150:complications / Q000473:pathology / Q000503:physiopathology*; D009433:Neural Inhibition; D009434:Neural Pathways / Q000503:physiopathology; D011597:Psychomotor Performance; D011930:Reaction Time; D012438:Saccades