Cognitive control and the underlying mechanisms in restless legs syndrome

Restless legs syndrome (RLS) is a sensory-motor disorder characterized by abnormal circadian rhythm with an increase in the severity of sensory and motor symptoms at night. Even though many neurological diseases have shown a strong nexus between motor and cognitive symptoms, to date, cognitive functions especially cognitive control in RLS has been poorly understood. Given that cognitive control is a key to leading a self-serving and successful life, including many aspects of employment, social life, and attaining long-term goals, this thesis aimed to examine cognitive control and the underlying mechanisms in RLS. Thalamic gamma aminobutyric acid (GABA), which has been linked to RLS sensory-motor symptoms, also plays an important role in cognitive control. Therefore, the potential relationship between thalamic GABA level and cognitive control in RLS was examined (Study I). RLS patients displayed reduced working memory-based control performances as compared to healthy controls. Elevated thalamic GABA was found to attenuate the observed control deficits in RLS, even though changes in thalamic GABA levels might not be the ultimate causes of these deficits. According to the modulatory effect of thalamic GABA on thalamic activity and thalamo-cortical connectivity, relatively higher GABA levels may have helped RLS patients compensate for their pathological changes such as thalamic hyperactivity and hypoconnectivity, which may underpin the observed control deficits. The critical feature of RLS, abnormal circadian rhythm is thought to be related to nocturnal striatal dopamine deficiency. Concerning the dopaminergic modulation of cognitive control, the circadian variation of cognitive control processes has been investigated (Study II & III). RLS patients displayed reduced attentional control (Study II) and automatic response activation (Study III) at night, which resulted from decreased activation within the extra-striate visual cortex, the superior parietal cortex, and the premotor cortex. As there were no activity changes within the prefrontal cortex, it is likely that cortico-basal ganglia cognitive loops were less prone to RLS. Instead, striatal dopamine deficiency at night may have influenced the cortico-cortical functional connectivity and cortico-basal ganglia motor loops in RLS. These findings not only shed light on the underlying mechanisms of cognitive control, but also advance early clinical treatment possibilities for cognitive changes in RLS patients. Furthermore, recent insights into daytime-related cognition may help patients develop a suitable daytime schedule to minimize the detrimental effects induced by cognitive deficits