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Bernard Pillon
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Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2005) 17 (12): 1886–1896.
Published: 01 December 2005
Abstract
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When a decision between alternative actions has to be made, the primate brain is able to uncouple motor execution from mental deliberation, providing time for higher cognitive processes such as remembering and reasoning. The mental deliberation leading to the decision and the motor execution applying the decision are likely to involve different neuronal circuits linking the basal ganglia and the frontal cortex. Behavioral and physiological studies in monkeys indicate that dopamine depletion may result in a loss of functional segregation between these circuits, hence, in interference between the deliberation and execution processes. To test this hypothesis in humans, we analyzed the movements of parkinsonian patients in a go/no-go task, contrasting periods of uncertainty with periods of knowledge about the rule to be applied. Two groups of patients were compared to healthy subjects: one group was treated with dopaminergic medication and the other with deep brain stimulation; both groups were also tested without any treatment. In healthy subjects, the movement time was unaffected by uncertainty. In untreated patients, the movement time increased with uncertainty, reflecting interference between deliberation and execution processes. This interference was fully corrected with dopaminergic medication but was unchanged with deep brain stimulation. Moreover, decision-related hesitations were detectable in the movements of dopamine-depleted patients, revealing a temporal coupling of deliberation and execution. We suggest that such coupling may be related to the loss of dopamine-mediated functional segregation between basal ganglia circuits processing different stages of goal-directed behavior.
Journal Articles
Preserved Adjustment but Impaired Awareness in a Sensory-Motor Conflict following Prefrontal Lesions
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2001) 13 (3): 332–340.
Published: 01 April 2001
Abstract
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Control of action occurs at different stagesof the executive process, in particular at those of sensory-motor integration and conscious monitoring. The aim of this study was to determine the implication of the prefrontal cortex in the control of action. For that purpose, we compared the performance of 15 patients with frontal lobe lesions and 15 matched controls on an experimental paradigm generating a conflict between the action planned and the sensory-motor feedback. Subjects had to trace a sagittal line witha stylus on a graphic tablet. The hand was hidden by a mirror on which the traced line, processed by a computer, was projected. Without informing the subjects, the line traced was modified by introducing a bias to the right, which increased progressively from 2° to 42°. To succeed the task, subjects had to modify their motor program and deviate their hand in the opposite direction. The sensory-motor adjustment to the bias was evaluated by the surface between the line traced and the ideal line to compensate for the deviation. The awareness of the conflict was measured by the angle of the bias at which subjects expressed the feeling that the line they traced was not the same as the line they saw. The deviation was similarly compensated for by patients and controls until24°. Then 14 controls but only3 patients were aware of a conflict. After that, the variability of performance increased significantly for the unaware patients. These results suggest that the prefrontal cortex is required at the level of conscious monitoring of actions, but not at the level of sensory-motor integration.