Frontal dysfunction in patients with restless legs syndrome performing a visual oddball task: an event-related potential source imaging study

Restless legs syndrome (RLS) is a sensorimotor neurological disorder that is accompanied by the compelling urge to move one's legs, and unpleasant, disturbing sensations in the legs. Several neuropsychological studies have shown that RLS is associated with deficits in cognitive functions, such as attention, working memory, and frontal executive function, presumably due to abnormal frontal activities. However, the mechanism underlying the cognitive deficits in RLS patients is mostly unknown. To investigate the cortical origin of cognitive dysfunction in RLS, we analyzed the P2 and P3 event-related potential (ERP) components evoked by a visual oddball task using distributed cortical source localization via low-resolution brain electromagnetic tomography (LORETA) algorithm. A total of 17 female drug-naive RLS patients and 13 healthy volunteers were enrolled. Multichannel ERPs were recorded while performing a visual oddball task. We identified that the P2 and P3 ERP components were significantly reduced in RLS patients. These patients showed a reduction of the cortical current source densities in temporal periods corresponding to P2 and P3, compared to normal controls. Significant differences between RLS patients and normal controls were mainly found in the frontal region; that is, in the medial prefrontal cortex at the P2 epoch and the anterior cingulate cortex at the P3 epoch. Our neurophysiological results imply that the abnormal activities in the frontal region results in a cognitive deficit in RLS patients, which should be compared with neuropsychological evaluations in a further study.