We know relatively little about why we sleep but researchers are finding that it is as important to our health as diet and exercise, and a lack of it has been linked with diseases such as diabetes, writes CLAIRE O'CONNELL
SLEEP: WE CAN spend as much as a third of our lives doing it. If something disrupts our usual patterns – maybe a new baby, a snoring partner or plain insomnia – we soon feel the effects. And there’s growing evidence that sleep disruption is associated with various diseases. Yet we still know relatively little about why we sleep in the first place.
“For something that we spend a very big period of our lives doing it’s really remarkable that in physiological terms there’s really no unifying theory on why we sleep,” says Dr Andrew Coogan, a lecturer in psychology at NUI Maynooth. “The strongest theory for why we sleep is to do with allowing our brains to integrate information that we have acquired throughout the previous day.”
Studies on memory point to sleep’s enhancing effects on cognition, he adds. “When you get individuals to learn a task then allow them to sleep and retest them the following day, they perform significantly better than those who aren’t allowed to sleep.”
As diurnal creatures, we tend to be awake in the day and sleep during the night, but why are we primed to do this?
Two systems are thought to play roles: the “sleep homeostat” and our internal circadian clock, explains Coogan. The sleep homeostat refers to how levels of various chemicals – including neurotransmitters in the brain – build up and act as a signal to the body about how long it has been awake.
Meanwhile, our circadian clock cycles over the course of about 24 hours and, although it can be affected by external factors such as light, there is also an inherent internal rhythm to it. “If you think about the sleep homeostat as the hourglass and the circadian [machinery] as a clock, when the two talk together it determines when we go to sleep,” says Coogan.
Yet while it’s straightforward to think of slumber as downtime for the brain, it turns out there’s quite a bit going on in the land of nod.
“Being asleep is not just not being awake,” says Coogan. “Sleep is an active process, there are specific patterns of activity in the brain that are associated with sleep.”
We cycle through various stages of sleep, including phases of slow-wave sleep that appear to be restorative, and rapid-eye-movement or REM sleep.
“We dream mostly during REM sleep,” says Coogan. “Then we tend to go back into slow-wave sleep, and slow-wave sleep tends to be highly amnesic – so to remember a dream you have to wake up during or very soon after.”
So much for normal sleep. But what about when things go awry with sleeping patterns? Poor sleep is associated with conditions such as depression, bipolar disorder, schizophrenia and Alzheimer’s disease, says Coogan, who also points out a link between shortened sleep and the risk of diabetes. “If you are not getting enough sleep, that is predisposing you to developing type-two diabetes,” he says.
His team has been looking at links between circadian rhythms and adult attention-deficit hyperactivity disorder.And in a recent study published in Molecular Psychiatry, Dr Coogan’s group found that circadian rhythms were unusual in adult patients with ADHD.
“Their clock was out of sync,” he says. “We have a feeling that this might be an important component of the symptomatic picture in adult ADHD.”
Sleep is quite literally the “sleeping giant” of health research, according to Dr Conor Hanley, CEO of BiancaMed, a company that has developed non-invasive technology to get the measure of a person’s sleep.
“Sleep is recognised as a major component of health, alongside diet and exercise,” says Hanley. “While diet and exercise are now well tracked and managed, sleep has remained the only major health metric to be poorly monitored.”
Hanley co-founded BiancaMed with Prof Conor Heneghan and Dr Philip de Chazal from University College Dublin, who were looking for a way to help doctors screen for the condition sleep apnoea, in which a person has abnormal pauses in breathing during their sleep.
“Most of the current sleep-apnoea diagnosis is currently done in a hospital, and they were looking at how to enable the doctor to perform a convenient home test,” says Hanley.
The approach they came up with uses sensitive radio-frequency motion sensors to detect breathing and movement. “The technology is based on ultra-low power radio waves that are transmitted and then reflected off a person’s skin, and the resulting echo is used to determine the person’s movement, respiration and heart rate.”
Crucially, the sleeper doesn’t need to wear or be hooked up to any device, so they can just sleep as they usually do, with the device nearby. “It automatically measures your data without any contact,” says Hanley.
“It reports on your sleep in the morning and also can send the data to the cloud where it can be further analysed, trended and stored. For people with chronic disease, we hope that by measuring sleep and breathing in the home we will help doctors to have information about the status of a patient’s condition so they can be better managed, resulting in better outcomes.”
The meaning of dreams
DREAMS CAN BE vivid, scary, enlightening or simply odd: and often scurry away like mice when we wake, becoming hard to recall.
But why do we do it? “We don’t know exactly why we dream, but some interesting research has demonstrated that the more we dream of emotional events from our lives, the better equipped we are to handle and cope with those events,” says Dr Caroline Horton, a senior lecturer in psychology at Leeds Metropolitan University. “So there is likely to be some emotional function of dreaming.”
Recent research, including work in Dr Horton’s own lab, suggests that dreaming may have links with the processes of memory consolidation in sleep. “When we sleep, we re-activate and re-jumble experiences and information that we have recently learned. So sleep helps us to set down this new information into newly re-organised, long-term memory structures – in other words, sleep helps us to remember,” she says. “Dreaming may well add to this, but we do not know yet as to whether dreaming simply reflects these processes – that is, as our experiences are re-activated we experience them as thoughts, which we sometimes then recall as dreams. Or whether the dream process adds something unique and special to these processes.”
Horton is currently looking at the role of dreaming in a series of diary studies. She wants to see whether dreaming of events from our waking lives helps us to better remember those events.
“Preliminary results indicate that we dream of and better recall emotional events, so the function of dreaming may well be to enable us to remember particularly salient aspects of our waking lives, so we can remember them and know how to behave in future emotional situations,” she says.
