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 precursor to neurodegenerative diseases like Parkinson's disease (PD). Research is mainly focused on identifying markers for predicting the progression of these diseases early. Some authors hypothesized a link between dream activity in RBD and biological processes underlying neurodegeneration. Therefore, our study aims to investigate oneiric features in association with sleep patterns and neuropsychological measures in a group of iRBD patients. Method: Thirty-one individuals diagnosed with iRBD at IRCCS San Raffaele in Milan (mean age: 68.03 ± 7.29) were recruited. iRBD patients will undergo a video-polysomnographic (vPSG) and a neuropsychological assessment will be conducted prior to any experimental session. Upon morning awakening, audio-recording of dream recall (DR) and completion of a questionnaire related to self-assessed dream characteristics were required. Results: Fifteen iRBD patients reported at least one dream (48.4% of the sample). Correlational analyses (Spearman's Rho) showed that (a) the number of DR was positively correlated with the percentage of stage 1 NREM Sleep (Rho = 0.684, p = 0.005); (b) the total word count of DR was positively correlated with the Mini Mental State Examination assessing the level of cognitive decline (Rho = 0.551, p = 0.033); and (c) the emotional intensity of DR, particularly characterized by negative emotions, were negatively correlated with the attentive matrices scores (Rho =  0.711, p = 0.003). Conclusion: According to the literature, our preliminary results support the 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 with poorer attentional performance. Previous studies found that unpleasant emotions and aggression were associated with frontal deficits in iRBD. Moreover, attentional skills most reliably predict neurodegenerative disorder conversion. Finally, we found that the length of dream reports is correlated with lower cognitive decline, consistent with the idea that there is continuity between cognitive functioning in wakefulness and sleep. Overall, the findings suggest that dreaming can provide relevant information about the cognitive functioning of RBD patients, providing possible markers for conversion to alphasynucleinopathies as PD.