Dreaming in RBD: A window into neurodegenerative mechanisms?

Introduction: Isolated Rapid Eye Movement Sleep Behavior Disorder(iRBD) is a condition where muscle atonia during REM sleep is lost,leading to individuals acting out their dreams. It is considered a precursorto neurodegenerative diseases like Parkinson's disease (PD).Research is mainly focused on identifying markers for predicting theprogression of these diseases early. Some authors hypothesized a linkbetween dream activity in RBD and biological processes underlyingneurodegeneration. Therefore, our study aims to investigate oneiricfeatures in association with sleep patterns and neuropsychologicalmeasures in a group of iRBD patients.Method: Thirty-one individuals diagnosed with iRBD at IRCCS SanRaffaele in Milan (mean age: 68.03 ± 7.29) were recruited. iRBDpatients will undergo a video-polysomnographic (vPSG) and a neuropsychologicalassessment will be conducted prior to any experimentalsession. Upon morning awakening, audio-recording of dream recall(DR) and completion of a questionnaire related to self-assessed dreamcharacteristics were required.Results: Fifteen iRBD patients reported at least one dream (48.4% ofthe sample). Correlational analyses (Spearman's Rho) showed that(a) the number of DR was positively correlated with the percentage ofstage 1 NREM Sleep (Rho = 0.684, p = 0.005); (b) the total wordcount of DR was positively correlated with the Mini Mental StateExamination assessing the level of cognitive decline (Rho = 0.551,p = 0.033); and (c) the emotional intensity of DR, particularly characterizedby negative emotions, were negatively correlated with theattentive matrices scores (Rho =  0.711, p = 0.003).Conclusion: According to the literature, our preliminary results supportthe hypothesis that a shallower sleep promotes DR. Not surprisingly,we found a high percentage of negative emotions in patients'dreams, and greater emotional intensity appears to be associated withpoorer attentional performance. Previous studies found that unpleasantemotions and aggression were associated with frontal deficits iniRBD. Moreover, attentional skills most reliably predict neurodegenerativedisorder conversion. Finally, we found that the length of dreamreports is correlated with lower cognitive decline, consistent with theidea that there is continuity between cognitive functioning in wakefulnessand sleep. Overall, the findings suggest that dreaming can providerelevant information about the cognitive functioning of RBDpatients, providing possible markers for conversion to alphasynucleinopathiesas PD.