OBJECTIVE: The restless legs syndrome (RLS) is characterized by sensory-motor symptoms which usually occur predominantly at rest in the evening and at night. It is assumed that this circadian rhythm is caused by low dopamine levels in the evening. Yet, it has never been investigated whether RLS patients show diurnal variations in cognitive functions modulated by dopamine and what neurophysiological and functional neuroanatomical processes underlie such modulations. METHODS: We used a Simon task combined with EEG and source localization to investigate whether top-down response selection and/or automatic visuo-motor priming are subject to diurnal changes in RLS patients, as compared to matched healthy controls. RESULTS: We found that RLS patients showed better task performance due to reduced visuo-motor priming in the evening, as reflected by smaller early lateralized readiness potential (e-LRP) amplitudes and decreased activation of the superior parietal cortex and premotor cortex. Top-down response selection and early attentional processing were unaffected by RLS. CONCLUSIONS: Counterintuitively, RLS patients show enhanced task performance in the evening, i.e. when experiencing dopaminergic deficiency. Yet, this may be explained by deficits in visuo-motor priming that lead to reduced false response tendencies. SIGNIFICANCE: This study reveals a counterintuitive circadian variation of cognitive functions in RLS patients.

Cognitive Neurophysiology Department of Child and Adolescent Psychiatry Faculty of Medicine of the TU Dresden Schubertstr 42 01307 Dresden Germany

Cognitive Neurophysiology Department of Child and Adolescent Psychiatry Faculty of Medicine of the TU Dresden Schubertstr 42 01307 Dresden Germany; Experimental Neurobiology National Institute of Mental Health Topolová 748 25067 Klecany Czech Republic

Cognitive Neurophysiology Department of Child and Adolescent Psychiatry Faculty of Medicine of the TU Dresden Schubertstr 42 01307 Dresden Germany; MS Centre Dresden Faculty of Medicine of the TU Dresden Blasewitzer Str 43 01307 Dresden Germany

Department of Neurology Technische Universität Dresden Fetscherstraße 74 01307 Dresden Germany

Department of Neurology Technische Universität Dresden Fetscherstraße 74 01307 Dresden Germany; German Center for Neurodegenerative Diseases Dresden Arnoldstraße 18 01307 Dresden Germany

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