Sleepwalkers who jump out of windows or fall down stairs don’t immediately feel the painful effects of their nocturnal excursions, according to a new study published in the journal Sleep. Instead, they often remain asleep for several hours following their accidents and only feel pain once they wake up.
The link between pain and sleepwalking – also called somnambulism – has invited speculation from scientists for centuries. In the late 1800s, for example, Charles Darwin’s grandfather Erasmus proposed that such unconscious expeditions may serve to relieve bodily or mental discomfort. Yet the new study, led by Dr Regis Lopez of Hospital Gui-de-Chauliac in Montpellier, has thrown up some surprising findings that highlight the paradoxical connection between sleepwalking and suffering.
Intriguingly, the paper indicates that sleepwalkers are roughly four times more likely than non-sleepwalkers to have a history of headaches, and 10 times more susceptible to migraines. This would appear to support previous studies that indicate a higher prevalence of somnambulism among sufferers of chronic pain than non-sufferers, even though the reasons for this are not fully known. However, what the researchers found most surprising was the apparent inability of sleepwalkers to feel pain while in their unconscious yet mobile state.
Of the 47 participants who claimed to have suffered an accident while sleepwalking, 79 percent said they did not feel any pain at the time, and remained asleep despite being injured – in some cases rather severely. For instance, among the participants in the study was a patient who had sustained several fractures after jumping from a third-floor window, yet felt nothing until waking up several hours later. Another fell from the roof of his house, breaking his leg in the process, but did not become aware of his injury until morning.
Because of this, the researchers have suggested a connection between dissociated brain activity and the dysregulation of nociceptive pain – meaning the pain caused by the stimulation of the nerves found in body tissue. Dissociation is something that has often been correlated to sleep and nocturnal disorders, and refers to the disruption of the integration of consciousness, memory, and perception. In other words, the parts of the brain that are responsible for these separate functions become subdivided, enabling some to be activated independently of the others.
In the case of sleepwalking, the study authors hypothesize a dissociated arousal state in the motor and cingulate cortices, which are partially responsible for nociceptive regulation. As a result, the transfer of sensory information to the brain is blocked, enabling sleepwalkers to injure themselves without feeling any pain.