Neglect-like behavior in healthy subjects

Evidence has been reported favoring the view of a dual mode of space representation for action and spatial cognition. While the dorsal system seems to be mainly involved in direct coding of space for action by means of several effector-specific representations, the ventral system appears to be responsible for more enduring and conscious representations underlying spatial cognition and awareness. In accordance with this view are recent studies documenting dissociations between exploratory and goal-directed movements in patients with brain damage. Patients with neglect exhibit a spatial bias of exploratory movements to the ipsilesional side, while goal-directed movements land precisely on target. The exploratory bias was found susceptible to asymmetric sensory stimulation such as caloric vestibular stimulation, inducing transient reduction of contralateral neglect. The present study compared exploratory and goal-directed hand movements in healthy subjects following cold caloric stimulation of the right vestibular organ. We observed a rightward shift of tactile exploration, while goal-directed pointing remained unaffected. Asymmetric vestibular stimulation in healthy subjects thus produced a neglect-like behavior with a similar dissociation between impaired exploratory and nonimpaired goal-directed hand movements. The stimulation provoked a further, very characteristic symptom of neglect patients: a deviation of spontaneous head orientation toward the right. The present observations strengthen substantially the assumption of different modes of space representation for action and spatial cognition in humans.