There can be few feelings more comforting than the warm, fuzzy envelopment of sleep as you drift off after a hard day’s work.
Now researchers may have found a clue as to why sleep can make us feel so good.
They have discovered a key brain circuit that acts as a ‘sleepiness switch’ but is also a major component of our internal reward system.
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Scientists have discovered a key brain circuit in helping us drift off to sleep (stock picture). The ventral tegmental area is also involved in our reward system that helps motivate us to do tasks, but when it is inhibited, mice were found to quickly fall asleep
The circuit of neurons, known as the ventral tegmental area, helps to motivate us to perform behaviours like looking for food, having sex or fleeing from predators.
THE DISCOVERY COULD LEAD TO NEW SLEEP TREATMENTS
By using drugs that counter the amount of dopamine produced by the neurons in the ventral tegmental area, it may be possible to help those suffering from sleeping disorders.
The researchers behind the new study say that drugs targeting these nerve cells could also help people suffering from neurological conditions such as schizophrenia or bipolar disorder, which are characterized by sleep-wake cycle disturbances.
“It could be that merely solving the sleep-wake part will clear up a lot of symptoms,” said Dr Luis de Lecea.
‘We have plenty of drugs that counter dopamine.
‘Perhaps giving a person the right dose, at just the right time, of a drug with just the right pharmacokinetic properties so its effect will wear off at the right time would work a lot better than bombarding the brain with benzodiazepines, such as Valium, that knock out the entire brain.’
But it also appears to play an important role in helping us prepare for bed.
Researchers studying mice found that when they inhibited this part of the brain, the animals spent their time meticulously building nests before conking out.
Dr Luis de Lecea, a psychiatrist at Stanford University’s school of medicine, said this could be a key part of our brain’s preparations to drift off to sleep.
By reducing our motivation to do other things, our brains can help us to slip into a more peaceful sleep.
He said: ‘This has potential huge clinical relevance.
‘Insomnia, a multibillion-dollar market for pharmaceutical companies, has traditionally been treated with drugs such as benzodiazepines that nonspecifically shut down the entire brain.
‘Now we see the possibility of developing therapies that, by narrowly targeting this newly identified circuit, could induce much higher-quality sleep.’
The ventral tegmental area, or VTA, is known to be the origin of a number of nerve fibres that produce dopamine – the hormone involved in reward and happiness.
A number of these fibres lead to the nucleus accumbens, a forebrain structure implicated in feelings of pleasure due to anticipation or in response to obtaining an object.
The ventral tegmental area, or VTA (show in image above), is known to play a role in the brain’s reward system, helping to motivate us to seek out food or sex. But a reduction in its activity appears to play a key role in helping us prepare for bed
In the study, which is published in the journal Nature Neuroscience, the scientists bioengineered mice so they could excite, suppress and monitor these nerve cells.
When the mice woke up and were awake, activity levels of these dopamine-secreting nerve cells in the VTA were elevated.
The activity decreased as they fell asleep and remained low during their sleep.
Researchers say this makes sense as otherwise we would find our sleep being disturbed by sudden cravings for food or other desires.
When the scientists activated the cluster of neurons in slumbering mice, they woke up and stayed awake for long periods.
If the researchers suppressed the activity of these nerve cells, the mice quickly fell asleep and would not rouse even if they were given presented with the smell of food, a female or fear-inducing fox urine.
Watching TV or using a smartphone before bed can make it harder to drop off (stock picture of woman asleep in front of the television) for some people and the researchers say the role of the VTA in this process may be important
When the mice were placed in a new case, if their VTA activity was suppressed, they would spend 45 minutes building nests before going to sleep.
Dr Ada Eban-Rothschild, who was the lead author of the study and also works at Stanford University, said: ‘They were really careful about it.
‘If we put the nest they’d already built in their usual cage into the novel cage, they climbed in and went right to sleep.’
Crucially, the ‘sleepiness switch’ is involved in production of dopamine, the brain chemical behind the buzz of hard drugs, junk food and falling in love.
A pill that turns down the switch should cut dopamine levels and make it easier to fall asleep.
Dr de Lecea added the findings could help to explain why exposure to smartphones or other screens just before bed can make it harder to drop off.
He said: ‘This is the first finding of a sleep-preparation starter site in the brain. It’s likely we humans have one, too.
‘If we’re disrupting this preparation by, say, reading email or playing videogames, which not only give off light but charge up our emotions and get our VTA dopaminergic circuitry going, it’s easy to see why we’re likely to have trouble falling asleep.’
SLEEPING NAKED COULD HELP YOU HAVE A BETTER KIP
Skip the flannel pajamas and over-sized t-shirts – experts say sleeping au naturel is better for your health.
Researchers found that sleeping naked is not only comfortable, but it regulates your skin temperature, preventing you from waking in the middle of the night.
Forgoing clothes at bedtime also keeps bacteria that thrive in warm moist areas at bay, and it boosts your immune system if you sleep naked with your partner.
Only 12 percent of Americans sleep naked, according to a poll from the National Sleep Foundation, but it is highly recommended by both researchers and doctors.
The human body is designed to decrease in temperature during sleep, and not only does sleeping in the nude keep you comfortable through the night, but it determines when your body is ready to fall asleep and when it is time to wake up.
One study found that even the slightest cooling of the skin helps individuals fall into a much deeper sleep, according to Seeker.
Cooling the body is especially beneficial to the elderly, and this research confirms previous studies that found warmer skin, in both humans and animals, disrupts sleep.