text: For most of us, the actions we perform in dreams stay safely in our inner dreamworlds. REM (rapid eye movement) sleep, in which the majority of dreams occur, is characterized by the relaxation of skeletal muscles (muscle atonia), except those controlling the eyes. Hence, even when we are involved in vigorous activity in our dreams, our bodies stay almost totally still.
  
  Except in cases of REM sleep behavior disorder, or RBD. Individuals with RBD lack muscle atonia during REM sleep, and often appear to be acting out their dreams. These dreams are, for unknown reasons, disproportionately frightening or violent in nature; someone awakened from an episode of dream enactment will often report that they were being attacked or chased. It is not uncommon for people with RBD to seriously injure themselves or their bed partners.
  
  There has been very little research on the prevalence of RBD; studies suggest that it may affect between .02 and .5% of the population. RBD has many potential causes: it may be associated with brain lesions, narcolepsy, alcohol withdrawal, post-traumatic stress disorder, and the use of certain drugs. When the cause of RBD can be determined, it is referred to as secondary or symptomatic RBD. However, there are many cases where the cause of the disorder cannot be discovered; this is called idiopathic RBD. For unknown reasons, those who suffer from idiopathic RBD are overwhelmingly male.
  
  On one hand, treatment of RBD is fairly straightforward: the disorder seems to respond well to clonazepam, a benzodiazepine. On the other hand, over 50% of people diagnosed with RBD will go on to develop Parkinson’s disease in the 12 years after their diagnosis. Parkinson’s disease has no cure and treatments like L-Dopa only work for a limited period of time. Thus, RBD may be less of a disorder in its own right and more of a harbinger of Parkinson’s or other neurodegenerative disorders.
  
  This idea seems to be borne out in recent research. Parkinson’s disease is caused by the death of dopamine-producing neurons in a brain region called the substantia nigra. A recent study using advanced neuroimaging techniques found that over 50% of individuals with RBD had hyperechogenicity of the substantia nigra, indicating that neurons there were dying. Furthermore, they found reduced presynaptic striatal dopamine transporter binding in 36% of participants, which is characteristic of Parkinson’s disease.
  
  When better treatments for Parkinson’s are developed, early and seemingly unrelated disorders like RBD may be used to diagnose Parkinson’s before too much damage has been done. Early treatment may help to slow the course of the disease and improve quality of life for many people. Until then, research on RBD raises new questions about the role of dopamine and the substantia nigra in mediating both pathological and normal REM sleep behavior.
  
  Sources
  
  Boeve, F. (2010). REM Sleep Behavior Disorder: Updated review of the core features, the RBD-neurodegenerative disease association, evolving concepts, controversies, and future directions. Annals of the New York Academy of Sciences, 1184: 15-54.
  
  Manni, R., Ratti, P.L., & Terzaghi, M. (2011). Secondary “incidental” REM sleep behavior disorder: do we ever think of it? Sleep Medicine; 12 Suppl 2: S50-53.
  
  Rupprecht, S., Walther, B., Gudziol, H., Steenback, J., Freesmeyer, M., Witte, O.W., Gunther, A., & Schwab, M. (2013). Clinical markers of early nigrostriatal neurodegeneration in idiopathic rapid eye movement sleep behavior disorder. Sleep Medicine, EPub.