In 2008 Brian Thomas got out of bed in the middle of the night and strangled Christine, his wife of 40 years, while she slept. In December 2010, an inquest declared her death was accidental, even though Brian had admitted to killing her. How? Brian Thomas was actually the tragic victim of a night terror and had killed his wife in his sleep.



The couple had been on a caravanning holiday when a group of youths had made them feel threatened earlier in the day. Later that night, Thomas had a terrifying nightmare and began to sleepwalk.

Thomas had told police that he thought he saw a man wearing jeans and a black fleece laying on top of Christine. He said he’d screamed at the man and grabbed him round the throat. But as he woke up, he found his hands were around Christine’s neck. When he realised what he’d done, it was too late, and he immediately rang the police.

Because of the extraordinary circumstances surrounding Thomas’s arrest, Dr Chris Idzikowski, the director of the Edinburgh Sleep Centre, was called in to examine him and try to determine exactly what happened that night. “We took sensors in and set up a sleep study in the prison,” says Idzikowski. “We measured brain waves, eye movement, chin and leg muscle tone, nasal airflow, respiratory effort and his oxygen levels.”

In these sleep recordings, Idzikowski was looking for any sleep behaviours that indicated Thomas’s account of events was plausible: that he was in fact sleepwalking. “I was looking for the triggers in sleep that can lead to sleepwalking events,” says Idzikowski, “things like obstructive sleep apnea – where your breathing is interrupted – or periodic limb movements where your legs or arms start to move in a fit-like manner. And in Mr Thomas’s case, these sorts of signs were pretty straightforward to find.”

More like this

This, together with witness accounts of his sleepwalking, helped to build a picture of someone suffering from an ambulatory parasomnia – an umbrella term that accounts for walking behaviours during sleep. Of course, this on its own wasn’t enough to deem someone innocent of murder.

“One never really has any absolute certainty in each case,” says Idzokowski, a regular expert witness in cases where parasomnias are involved. “After the sleep recordings, the case has to be dealt with like any other. Was there a motive? Witness accounts that show a lack of awareness or consciousness, or any that show confusion help – as do unusual stresses or sleep deprivation. There is, of course, the opportunity for malingering [exaggerating or feigning the condition] and I’m called in for the prosecution as much as I am for the defence.”

On his own

In Thomas’s case the evidence stacked up in his favour and he was acquitted. The Crown Prosecution Service at his trial made it clear that the psychiatrists treating him felt that a reoccurrence was very unlikely, but his release provided a rather unique problem. “Brian Thomas was rightly acquitted,” says Idzokowski. “But now the system won’t pick him up and there’s still an issue of whether it could happen again.”

Now, it’s up to Thomas to find treatment for his sleepwalking on his own. Although as Idzikowski goes on to explain there are worse outcomes. “There’s an old case, 60 or 70 years old, where a French detective on holiday was brought on board on a murder investigation. He ended up deducing that he’d committed the murder in his sleep. So when he was sentenced he was allowed to continue his work as a policeman, but had to sleep in the prison by night.”

Sleep circuitry

Cases like Brian Thomas’s are not uncommon. The last decade has seen a growing number of crimes involving sleepwalkers, including a well-publicised case where a man drove 20km, stabbed his mother-in-law to death and injured his father-in-law, all while asleep.

In fact, in the US, they’ve become so frequent that Dr Michel Cramer Bornemann, at the Minnesota Sleep Institute, set up the world’s first Sleep Forensics Lab to help settle cases where a sleepwalking defence is used.

According to Cramer Bornemann, a sleepwalker’s brain effectively ‘short circuits’ during the early hours of sleep allowing them to get up and start walking around. During sleep, the brain oscillates between different stages of activity, known as REM (Rapid Eye Movement) and non-REM sleep. During REM sleep, the brain stem paralyses the body to prevent us from acting out our dreams while the mind churns through the day’s events. To transition from this state to non-REM, a state of reduced activity, the brain’s synapses – the connections between neurones – start to ‘switch over’. In the average person, this change between phases happens smoothly four to six times a night. But for reasons we don’t yet understand, sleepwalkers suffer from what’s known as a ‘switching error’.

“Something in the switch between phases goes wrong, creating an aberrant electrical impulse that triggers an overlap between states,” says Cramer Bornemann. “You’re not fully in REM, so your muscles are relaxed, not paralysed, and you’re not fully in non-REM, so you can still be dreaming. In this state some of the brain’s processes will be awake while others are offline.”

But why does this lead to such peculiar, often violent, behaviour? “As with many things in neuropathology it’s to do with real estate.” says Cramer Bornemann. “Brain structures like the hypothalamus that regulate sleep sit next to the mid-brain where early evolved behaviours lie. So when this electrical impulse is sparked it also wakes up this part of the brain, leaving the moral areas, like the frontal cortex, asleep. This leaves nothing to inhibit your rage reaction while you’re sleepwalking.”

Headless chickens

These ‘primal’ areas in the mid-brain control automated behaviours. It’s the same type of brain structure that allows chickens to run around after their heads have been cut off. These brain areas are also responsible for ‘Highway Hypnosis’, in which people can drive a familiar route without remembering any details of the journey. The structures are known as central pattern generators. During the day, they’re usually controlled by the higher functions of the brain, but aren’t reliant on them.

“These pattern generators in primitive animals produce behaviours that maintain survival, like predatory, feeding and sexual behaviours,” says Cramer Bornemann. “Our highly evolved brain has been able to override these purely automated instincts, but they’re still definitely there. They’re activated in epilepsy too, which is why sleep fits look very similar to epileptic fits.” These primitive behaviours fall directly in line with the stereotypical acts carried out by sleepwalkers: feeding, sex and searching for objects.

The most violent murders tend to occur together with a night terror or after someone has tried to wake them, triggering an uninhibited rage response. In fact, on the rare occasions that a sleepwalker has been put into a brain scanner – a tricky task in itself – it’s revealed that while the frontal cortex remains dormant, the amygdala and limbic system – the emotional control centres of the brain – are over-active.

It seems that the faulty brain circuitry underlying this imbalance is inherited. While just two per cent of the population report sleepwalking as an adult, the children of sleepwalkers have a 50 per cent chance that they’ll do the same as adults. Though, it seems we are all at risk to an extent. About 12 per cent of children sleepwalk up to the age of 18. In most, as their brains mature, these errors are corrected, and they never do it again. Although remnants show up occasionally as twitches or jerks during sleep. In fact, Cramer Bornemann goes as far as to suggest that everyone has the potential to sleepwalk. “Sleepwalking could be a condition that resides within all of us. Under certain conditions the sleepwalking ‘werewolf’ is in us all, and we’re all prone to have an isolated episode of sleepwalking if a switching error occurs. All we need is something to destabilise our sleep.”

Sleep clean

It’s when normal sleep patterns are disrupted by stress, sleep deprivation, noise or other disturbances that we’re most at risk of sleepwalking. In his sleep clinic at the James Cook University Hospital, Dr Paul Reading can even trigger a sleepwalking event. “In the lab we can very reliably spark sleepwalking episodes, by depriving someone of sleep and then playing a loud noise in the middle of the night,” says Reading. “So maintaining good sleep hygiene is crucial to avoiding sleepwalking episodes.”

In particular, alcohol consumption can be a serious factor. Not because of the intoxication itself, but the secondary effects like a full bladder, a late night’s sleep or even a night on the sofa can create enough disruption to leave you susceptible to switching errors.

For the partners of sleepwalkers, Dr Reading recommends caution. “The first hour of sleep is crucial, if you can avoid any disturbances in this hour then all should be well. But if you still catch them sleepwalking then don’t wake them.” And for sleepwalkers themselves, Reading has one invaluable piece of parting advice. “Wear pyjamas to bed. You’d be amazed how many people that know they’re sleepwalkers still sleep in the nude. Especially if you’re on holiday at a hotel, where your sleep will naturally be disruptive, it can save everyone a lot of embarrassment.”


Follow Science Focus on Twitter, Facebook, Instagram and Flipboard


Daniel BennettEditor, BBC Science Focus

Daniel Bennett is the Editor of BBC Science Focus. He is an award-winning journalist who’s been reporting on science and technology for over a decade, writing about the science of serials killers, sandwiches, supernovae and almost everything in between.