What do you think is happening in the images below? Maybe the man is reaching for a glass of water on the bedside table, or perhaps he is moving to adjust his pillow?

You might be surprised to find out that this man is actually punching someone; or at least, he thinks he is.

He’s suffering from REM sleep behaviour disorder (RBD). These images are taken from a video recording showing a patient having a dream that he was fighting an attacker.

RBD is a parasomnia, a term describing abnormal behaviour during sleep. Notably, RBD has been linked to Parkinson’s disease and could be a potential early manifestation of the disease (Schenck and Mahowald, 1995).

In fact, researchers at the University of Minnesota found that 48 per cent of the patients they tested for RBD also had a neurodegenerative disorder.

Other studies looking at RBD have found even higher instances at 73 per cent and 92 per cent.

In these studies, Parkinson’s disease was one of the most common disorders associated with RBD. Other findings report that on average there is a gap of 10-13 years between being diagnosed with RBD and the later development of Parkinson’s symptoms (Schenck and Mahowald, 1995).

This data shows a close relation between the two disorders and suggest that RBD could be an important precursor to a more life altering disease.

One of the main features of RBD is a loss of the usual muscle paralysis that accompanies REM sleep. REM (Rapid Eye Movement) sleep is the stage of sleep when the most vivid dreaming occurs.

So anytime you wake up and remember your dreams, they most likely occurred during this phase of the sleep cycle.

In fact, brain activity during REM sleep is very similar to waking brain activity, which means that lots of different areas of the brain are highly active just like when we are awake.

During REM sleep, the activity of motor neurons in our nervous system, which usually send signals from the brain to the muscles, is suppressed when we sleep so that our bodies don’t move. This is called atonia.

In addition to this loss of REM atonia, the content of the dreams experienced in RBD is different to what you and I may usually experience.

We may have arguably more ‘normal’ dreams, like going on an adventure through the Amazonian rainforest with the cute professor from university you had a crush on (definitely not a personal account).

Unfortunately for patients with RBD, dreaming is a much more unpleasant experience.

A comprehensive literature review conducted by Schenck and Mahowald (1995) found that 87 per cent of patients reported dreams to be more vivid, full of action and violent compared to normal dreams.

In actuality, the dreams experienced by patients with RBD are usually severe nightmares, with one patient describing his experience of the condition as “violent moving nightmares”.

The most common storyline the dreams follow is one where the patient is defending themselves against another person or an animal. It is not uncommon for patients to shout, swear, punch, have a conversation and even run, all in their sleep during episodes of RBD.

Because of this, RBD can often cause injury both to the sufferer and the bed partner. Many patients report instances in which they were dreaming of protecting their wife against an attacker, only to wake up and realise that they were the ones attacking their wife.

Couples usually work out an alternative sleeping arrangement, such as different beds, so that one of them doesn’t get whacked in the head whilst snoozing.

Some patients have even used homemade solutions such as tying themselves to their bed using belts and ropes to avoid unconsciously throttling their partners.

So what exactly causes RBD? The short answer is we still don’t know.

Although the exact cause remains unclear, current research implicates the pons and the medulla, two areas that make up part of what is known as the brain stem.

Research suggests that there is a loss of brain cells in these areas, which then leads to the lack of
muscle atonia during REM sleep, which leads to dream enactment.

To further understand the mechanisms underlying RBD, scientists have turned to a source surprisingly close to home.

Cats have been used in experiments investigating REM-atonia because their sleep cycles can be easily identified using brain imaging techniques.

Like humans, they also have periods of REM and non-REM sleep, although these phases are shorter.

Experimenters inflict a lesion to a specific area of the brain stem to observe its effects on how the cats sleep.

If they behave differently compared to cats without the lesion (controls) then it can be inferred that this difference in behaviour was due to the lesion.

Studies using this method have found that lesioned cats experience a permanent loss of REM-atonia and even show ‘hallucinatory-type’ behaviour that is similar to the behaviour shown by humans acting out their dreams (Schenkel and Siegel, 1989).

Although there are obvious issues with relating data from cats to humans, this provides good evidence for the idea that the brainstem is involved in keeping the muscles paralysed during REM sleep.

The inability to voluntarily control your movement is also characteristic of Parkinson’s disease.

Parkinson’s is a neurodegenerative disorder- that means that there is a loss of neurons in the brain which are the cells responsible for communication.

More specifically, there is a death of the neurons involved in movement, known as dopamine neurons, which is what makes it harder and harder to control your movement.

This is why some patients will have an incessantly shaky hand- this is known as a tremour.

Dr Sixel-Doring and his colleagues in Germany investigated Parkinson’s patients who also had RBD.

They found that patients with RBD were older, had longer disease duration, were in more advanced stages of Parkinson’s, had more falls and experienced more psychotic symptoms.

Dr Sixel-Doring and his colleagues suggest that RBD could be important in signalling the advancement of Parkinson’s.

Compared to other neurodegenerative diseases, RBD is hard to diagnose in the early stages of Parkinson’s so it is important for future research to focus on designing treatments that are sensitive to the dynamics of RBD.

Although drug therapies exist for patients with RBD, so far nothing has succeeded in stopping it altogether.

Considering a large majority of RBD patients are likely to develop a neurodegenerative disease later on in life, the need for further research is fundamental to developing our understanding of disorders like Parkinson’s.

Future questions to be investigated include whether RBD could be used as an early predictor of neurodegenerative disease and why it is related to more severe Parkinsonian symptoms such as longer disease duration.

With the continuing advancement of neuroscientific research, we will be able to gradually uncover the complexities involved in shadowboxing in your sleep.

Sara Din is a cognitive rehabilitation assistant at BIS Services and holds a masters in Cognitive Neuroscience.