The science of insomnia

LONGEST-SLEEPING MAMMALS

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Light affects the sleeping pattern of blind people, as ganglion cells are different from those that allow us to see

The science of insomnia

Why checking your phone before bed could be spoiling your sleep

Mostofusexperienceinsomniaatsome point in our lives, fi nding it diffi cult to drift off and stay asleep despite having plenty of opportunity to. Typical causes of insomnia include stress and anxiety, but did you know that your gadgets could be to blame, too?

Our sleepiness and wakefulness throughout the day and night is regulated by our circadian rhythm. This is essentially our body clock, creating physical, mental and behavioural changes that occur in our bodies over a roughly 24-hour cycle. Circadian rhythms are found in most living things, including animals, plants and many tiny microbes, and are created by natural factors in the body. However, they also respond to signals from the environment, such as light, so that we remain in sync with the Earth’s rotation.

All forms of light, both natural and artifi cial, affect our body clock, as when the photosensitive retinal ganglion cells in our eyes detect light, they send this information to the suprachiasmatic nucleus (SCN) – the group of nerves in the brain that controls circadian rhythms. When light is detected, the SCN will delay the production of melatonin, a hormone that sends us to sleep. However, the retinal ganglion cells have been found to be particularly sensitive to the blue light with a short wavelength of 480 nanometres emitted by most computer, smartphone and tablet screens. Exposure to a lot of this type of light in the hours before we go to bed has been proven to suppress melatonin levels, making it diffi cult for us to get to sleep.

Theganglionlayer

Theretinaoftheeyecontainsa layerofphotosensitiveganglion cells,whichcontaina photopigmentmelanopsin, calledtheganglionlayer.

Light sensitivity

Unliketheother photoreceptorsin theeye, photosensitive ganglioncells contributelittleto vision,buttheyare sensitivetolight.

Suprachiasmatic nucleus

The suprachiasmatic nucleus is a tiny area of neurons, located in the hypothalamus area of the brain, which controls circadian rhythms.

Light sensitivity

Howlightaffectsyourabilitytosleep

Pineal gland

The suprachiasmatic nucleus sends information from the photosensitive ganglion cells to the pineal gland, located in the epithalamus section of the brain.

Optic nerve

The photosensitive ganglion cells have long fi bres that connect to the optic nerve and eventually reach the suprachiasmatic nucleus.

Melatonin

When the photosensitive ganglion cells detect darkness, a message is sent to the pineal gland to produce melatonin, a hormone that causes drowsiness.

Blocking blue light

The best way to reduce your exposure to blue light is to avoid staring at a screen in the two hours before you go to bed. Instead illuminate the room with the warmer longer-wavelength light from regular incandescent bulbs or even candles.

However, if you just can’t resist staring at your computer or phone before bed,thentherearewaysthat you can dosoandstillgetagood night’s sleep.Wearingspecialglasses with amber-colouredlenseswillfilter out blue, low-wavelengthlight, allowing youtostareatyourscreen for as longasyoulike.Companies such as Uvex(uvex-safety.co.uk) make blue-blocking glasses and gogglesinarangeofst Alternatively,youcould computersoftwaresuc (justgetflux.com)ands appssuchasTwilight(p com)thatautomatically screentofilteroutblue sunsetandsunrise,rep softer red light.

Filter out blue light with a pair of amber-tinted glasses or by using smartphone apps