REM sleep behavior disorder and Parkinson's: an early sign
What REM sleep behavior disorder and Parkinson's have in common: a 1,280-patient study, and new research on how the brain responds to the heartbeat.
The 30-second summary
- In REM sleep behavior disorder, the body acts out vivid, often violent dreams. It is one of the earliest warning signs linked to Parkinson's disease and dementia with Lewy bodies.
- In a study following 1,280 patients, 73.5% had developed a clear brain disease after 12 years. A new study found their brains respond differently to the heartbeat while they are awake.
- The new study is small (only 13 patients), and this brain signal is not a diagnostic test yet.
REM sleep behavior disorder is a condition where the body reacts strongly to vivid, often violent dreams: a sleeper may hit out or shout as if living the dream. Its link to Parkinson's is well documented: it is one of the earliest warning signs of the brain changes seen in Parkinson's disease and dementia with Lewy bodies, sometimes appearing years before diagnosis.
Here we explain what a large international study found after following patients for 12 years, and what a new 2026 study adds about how these patients' brains respond to their own heartbeat. This article is for understanding, not a diagnosis for you or anyone you know.
How does it work?
In REM sleep behavior disorder, the dream doesn't stay in the head: the body moves with it. Because these dreams are often vivid and violent, the sleeper may hit out, shout or move forcefully. Scientists see it as a very early stage of a group of brain diseases, the best known being Parkinson's and dementia with Lewy bodies.
The new study looked at something else: the quiet conversation between heart and brain. With every heartbeat, the brain produces a small electrical signal that can be measured, called the heartbeat-evoked potential. In awake patients, this signal was different over the front of the brain, between 305 and 445 milliseconds after the peak of each heartbeat.
Interestingly, the difference did not show up during sleep, in either deep sleep or REM sleep. It also wasn't explained by differences in the heart recording itself, meaning the change lies in how the brain receives the heartbeat, not in the heart.
How do we know?
In 2019, Postuma and colleagues published an international study in the journal Brain that followed 1,280 patients from 24 centres, all with a diagnosis confirmed by a sleep recording. The researchers measured how many went on to develop a clear brain disease over the years: about 6.3% per year, and 73.5% after 12 years of follow-up.
In 2026, Bernasconi and colleagues published a study in npj Parkinson's Disease that recorded brain activity and heartbeat through the whole night in 13 patients and 23 healthy people, comparing the heartbeat-linked brain signal during wakefulness and different sleep stages.
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And also
The longer a patient had had symptoms, the clearer the change in how their brain responded to their heartbeat. And in everyone, patients and healthy people alike, this response was weaker during sleep than while awake.
But keep in mind
- The large study followed patients over time: it shows the disorder is linked to later disease, not that it causes it.
- The new study is very small: 13 patients compared with 23 healthy people, so its results need to be confirmed in bigger studies.
- The brain difference appeared only while awake, not during sleep. The researchers say it may become a measurable marker in the future, not that it is a diagnostic test today.
- Both studies included patients whose diagnosis was confirmed with a full overnight sleep recording, so they say nothing about ordinary sleep talking or an occasional shout.
FAQ
What is REM sleep behavior disorder?
It is a sleep disorder in which the body reacts strongly to vivid, often violent dreams, so the sleeper may move, hit out or shout. The diagnosis is confirmed with a full overnight sleep recording.
Is acting out dreams a sign of Parkinson's?
REM sleep behavior disorder is one of the earliest warning signs linked to Parkinson's disease and dementia with Lewy bodies, sometimes years before diagnosis. This link was found in confirmed patients, not in every kind of movement during sleep.
Does everyone with REM sleep behavior disorder get Parkinson's?
No. In a study of 1,280 patients, about 6.3% per year developed a clear brain disease, reaching 73.5% after 12 years. Of those, 56.5% showed parkinsonism first and 43.5% dementia first.
Can a brain test spot REM sleep behavior disorder while awake?
A small 2026 study found that the brain's response to the heartbeat differs in awake patients. The researchers see it as a possible future marker, not a test in use today.
Sources
- 1Risk and predictors of dementia and parkinsonism in idiopathic REM sleep behaviour disorder: a multicentre studyBrain (Postuma et al., International RBD Study Group) · 2019
- 2Altered heart-brain coupling in awake patients with isolated REM sleep behaviour disordernpj Parkinson's Disease · 2026
- 3Brain responses to heartbeat are altered in patients with iRBDMedical Xpress · 2026
These are the original sources; we only explain them. Read them yourself.
Science information for education only; it does not replace medical advice.
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