Cortical afferent inhibition is reduced in patients with idiopathic REM sleep behavior disorder and cognitive impairment: A TMS study

ObjectivesImpaired cognitive profile and electroencephalography (EEG) slowing have been reported in patients with REM sleep behavior disorder (RBD), but the neurobiological significance of these findings remains unknown. The cholinergic system is known to play a key role in all attentional processes and cognitive functions. A transcranial magnetic stimulation (TMS) protocol may give direct information about the function of some cholinergic circuits in the human brain; this technique relies on short latency afferent inhibition (SAI) of the motor cortex. The objective of this study was to test the hypothesis that cognitive performance and cortical activation in RBD patients are associated with a dysfunction of the cholinergic system.MethodsWe applied the SAI technique in a group of 10 patients with idiopathic RBD (iRBD) and compared the data with those from a group of 15 age-matched healthy subjects. All the iRBD patients and the control subjects also underwent an extensive neuropsychological evaluation.ResultsMean SAI was significantly reduced in patients with iRBD when compared with controls. Neuropsychological examination showed mild cognitive impairment in six out of the 10 iRBD patients. SAI values correlated strongly with tests measuring episodic verbal memory and executive functions.ConclusionsThese results support the hypothesis of cholinergic dysfunction in some patients with iRBD who develop cognitive impairment. Our findings raise the possibility that the presence of SAI abnormalities may indicate increased risk of cognitive impairment in patients diagnosed with iRBD.