Just a single night’s lack of sleep can make people more sensitive to pain, warns new research.
It activates neurons in an area of grey matter that senses afflictions – and switches off those that dampen them down, according to the study.
Researchers say their findings provide the first brain-based explanation for the well-established between shut-eye and physical discomfort.
And they suggest more attention should be paid to the importance of decent rest in the recovery of patients in hospital.
Disturbed nights on the noisy ward could prolong the agony of sickness and injury, say neuroscientists.
Dr Matthew Walker of UC Berkeley applied uncomfortable levels of heat to the legs of 24 healthy young adults while scanning their brains. Those who’d slept well were less sensitive to pain
Dr Matthew Walker, a self-professed ‘sleep diplomat’ of California University, Berkeley, said: ‘If poor sleep intensifies our sensitivity to pain, as this study demonstrates, then sleep must be placed much closer to the center of patient care, especially in hospital wards.’
He and his PhD student Adam Krause applied uncomfortable levels of heat to the legs of two dozen healthy young adults – while scanning their brains.
That showed the neural mechanisms that pick up, evaluate and activate relief to natural pain signals are disrupted when operating on insufficient sleep.
The fact pain sensitivity increased in the brain’s somatosensory cortex came as no surprise.
But what shocked the team was the ramped down reaction in the nucleus accumbens – reward circuitry that releases the ‘feel good’ chemical dopamine to reduce pain.
Dr Walker said: ‘Sleep loss not only amplifies the pain-sensing regions in the brain – but blocks the natural analgesia centers, too.’
The study, published in JNeurosci, sheds light on the self-perpetuating cycles contributing to the overlapping global epidemics of sleep loss, chronic pain and even opioid addiction.
A 2015 National Sleep Foundation poll in the US found that two in three chronic pain patients suffer from reoccurring sleep disruptions.
Almost four in 10 admitting they do not get the recommended minimum of seven hours a night.
Another key brain region found to slow down in the sleep-deprived brain was the insula.
This evaluates pain signals and places them in context to prepare the body to respond.
Lead author Mr Krause, a member of Dr Walker’s Center for Human Sleep Science lab, said: ‘This is a critical neural system that assesses and categorizes the pain signals and allows the body’s own natural painkillers to come to the rescue.’
To further test the sleep-pain connection in more common daily-life scenarios the researchers surveyed more than 230 adults of all ages nationwide via Amazon’s Mechanical Turk online marketplace.
Respondents were asked to report their nightly hours of sleep as well as their day-to-day pain levels over the course of a few days.
Results showed that even minor shifts in their sleep and wake patterns were correlated with pain sensitivity changes.
Mr Krause said: ‘The results clearly show even very subtle changes in nightly sleep – reductions that many of us think little of in terms of consequences – have a clear impact on your next-day pain burden.’
For the experiment each participant’s baseline pain threshold after a full night’s sleep was recorded.
The researchers did this by gradually increasing heat levels to the skin of their lower left leg while measuring brain activity in an fMRI (functional Magnetic Resonance Imaging) scanner.
The volunteers rated their thermal pain on a scale of one to 10 and reported, on average, discomfort at around 111 degrees Fahrenheit – roughly 44 degrees Celsius.
This enabled the researchers to compare how their individual pain threshold changed by repeating the procedure after a sleepless night.
The vast majority reported feeling pain sooner – at around 107 degrees Fahrenheit – after lack of sleep.
Mr Krause said: ‘Across the group, they were feeling discomfort at lower temperatures, which shows their own sensitivity to pain had increased after inadequate sleep.
‘The injury is the same, but the difference is how the brain assesses the pain without sufficient sleep.’
Meanwhile, brain imaging after a sleepless night showed marked increases in activity in the somatosensory cortex and deactivation in the nucleus accumbens and insular cortex.
This indicated malfunctions in the neural mechanisms that manage physiological responses to painful stimuli.
Dr Walker, author of the bestseller Why We Sleep, said: ‘The optimistic takeaway here is sleep is a natural analgesic that can help manage and lower pain.
‘Yet ironically, one environment where people are in the most pain is the worst place for sleep – the noisy hospital ward.’
His goal is to work with hospitals to create more sleep-friendly inpatient facilities.
He added: ‘Our findings suggest patient care would be markedly improved, and hospital beds cleared sooner, if uninterrupted sleep were embraced as an integral component of healthcare management.’