The neurobiology of sleep

Ah, sleep. We spend about a third of our lives at it, if we are lucky. But what exactly is it? Why do we need so much of it, and what is the relationship between sleep and health?

In this article, we explore such questions and consider one or two surprising facts about sleep. Perhaps one of our favourite pastimes, in which we adopt a stereotypical horizontal posture and drift off into a blissful state of sub-conscious rest, our sleep behaviour is as natural to us as breathing and just as crucial. From power naps to Sunday lie-ins, you snooze, you win.

Sleep behaviour

The first thing to note is that sleep is a cyclic and circadian behaviour common to many species, from human beings to fruit flies. As a behaviour, sleep remains highly conserved and important. We humans sleep approximately 8 hours per day on average, so by the time we reach the ripe old of age of 90, we will have spent about 32 years sleeping. Such a huge outlay of time must mean that sleep is vital for our survival and wellbeing, or one would assume our species would have selected out of it long ago.

So how is it that sleep helps us thrive? Sleep can be viewed as a manifestation of neurobiological processes that serve to protect us, and support our healthy functioning. A person sleeping has less motor activity and movement and is less able to respond to environmental stimuli generally, giving the body time to re-charge each night. Sleep is not a dormant state in terms of brain activity (which is shown to exhibit periods that are just as active as when we are awake), though it does act as a form of re-set for the brain, our body and our cells. For example, sleep is beneficial for stem cell regeneration, according to this study.

Pitch black

Night is key, though not the whole story. Sleep is a circadian pattern that is generated endogenously (it happens internally) and while sleep typically descends upon us sometime after sunset, circadian rhythms are a pattern set by the body in conjunction with the light-dark cycle. The brain region involved in circadian rhythms is the suprachiasmatic nucleus, or cells that form part of the hypothalamus, found next to the optic chiasm.

Since no thing in nature is accidental, this tells us that light is an important factor in our sleep-wake behaviour and equally that dark is important for us too. We tend to want to stamp out that crack in the blind in order to settle off to sleep and black-out blinds or an eye mask actually benefit the brain as well as making us feel more relaxed and cosy. We love a Desmond and Dempsey eye mask. See article and study findings here. Sleeping in the dark is most relaxing and has also been shown to have anti-ageing benefits. Studies have demonstrated that cellular regeneration is more active when the body is in a total resting state in the absence of light. This increased level of regeneration leads to anti-inflammatory and hormonal balancing effects which in turn help the body to heal faster and slow down the ageing process.

The connection between light and sleep is an interesting one. The light spectrum is electromagnetic radiation or wavelengths that are visible to the human eye, involving different colours of light, including blue light. Blue light is known to disturb our sleep patterns because it is picked up by retinal ganglion cells that influence the suprachiasmatic nucleus. Retinal ganglion cells express a photopigment named melanopsin, which feeds molecular information to the suprachiasmatic nucleus. Melanopsin is sensitive to blue light wavelengths. So we can think of sleep as being affected by rhythmical and circadian stimuli such as light, and that falling asleep happens in stages, or waves, as we slowly drift off.

Brain waves

Sleep is a much studied phenomenon and we know what kind of electrical activity is going on in the brain by recording its activity using an electroencephalogram (EEG). When a person falls asleep, activity shifts from the typical waking state pattern of desynchronised activity and alpha rhythms, to the theta range (4 Hz to 7 Hz wavelengths). As sleep deepens, the EEG rhythm drops further and super slow delta waves begin to appear, known as K-complexes or “sleep spindles”, which are flowing, waxing and waning instances of alpha-frequency EEG.

In still further deeper sleep, slower frequencies take over, with longer periods of delta activity. As our sleep state progresses, we enter periods of lighter sleep, more akin to our wakeful state, involving increased theta activity. During this time, a persons’ muscle tone changes from low but constant movement to an absence of muscle tone (atonia) and a persons’ eyes might move, describing this stage of sleep as REM sleep, or rapid eye movement sleep. This is also our dream state, where we recall events and interactions from our waking state or from our imagination.

Natural neurobiology

The transition from wakefulness to sleep is naturally governed by our neurobiology. As neurologist Antonio Damasio explains, based on both neural and chemical pathways, certain nuclei in the brain stem tegmentum and the hypothalamus, act on the cerebral cortex to enhance vigilance (resulting in wakefulness) or reduced vigilance (promoting sleep). (Antonio Damasio, “Self Comes to Mind”, pg. 197).

Specific sets of neurons in the anterior hypothalamus, particularly from the ventrolateral pre-optic nucleus, are active during sleep. These neurons produce GABA (Gamma-aminobutyric acid), an amino acid and neurotransmitter which reduces neuronal excitability in the nervous system, as well as galanin, an amino acid and inhibitory neuropeptide implicated in many functions across the central and peripheral nervous system and endocrine system, such as feeding, nociception, learning, memory and, stress response.

The activation of the pre-optic ventrolateral nucleus inhibits ascending pathway neurons that promote wakefulness, and thus induce sleep. During our waking hours, we “accumulate” the molecules such as those described above and others, that make us want to fall asleep each night. A separate molecule implicated here is adenosine, a purine nucleoside base and molecule known as adenosine triphosphate (ATP), used throughout the body in metabolic processes. Extracellular or “waste” adenosine builds up throughout the daytime and declines during sleep, when our body and brain is resting. During sleep, our body is restoring itself and so sleep is an important factor in metaregulation and homeostasis. See study here.

Glial cells in the brain begin “hoovering” up any discarded cell fragments and play a role in the re-cycling of neurotransmitter. Also, the glymphatic system, and specifically the action of cerebral spinal fluid helps to cleanse toxins from the brain at night, as described here. So all in all, our brain and body in undertaking a repair and renewal operation while we are sleeping, during which time our energy and metabolic demands are lower.

Brain anatomy

The hypothalamus is a crucial area of the brain that performs many functions, from ensuring homeostasis to regulating the endocrine system (including hormone levels) though its interaction with the pituitary gland, and the autonomic nervous system. The autonomic nervous system in turn is responsible for the regulation of automatic functions in the body such as digestion, breathing and heart-rate, as well as our emotional processing ability. Pretty fundamental stuff.

The sleep-nervous system connection is core to our healthy functioning. Not to mention that the hypothalamus works together with the hippocampus, another limbic brain structure, one that is credited with modulating learning and memory as well as metabolic and emotional processing. Sleep also promotes mRNA translation, an important step in DNA synthesis and cell renewal, including processes essential for memory encoding and consolidation.

The sleep bank

The amount of sleep recommended depends upon our age and developmental requirements. Babies sleep most of the time and toddlers and infants need 12 hours plus per day. By the time children are in junior school, they still need upwards of 10 hrs per day just to keep up. This supports this body in replenishing its energy and supports the encoding of learning and memory. Bedtime stories and reading are especially important, before little ones are too sleepy, as learning recall is higher as a result. See studies here for further information (https://pubmed.ncbi.nlm.nih.gov/24329882/). (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7305149/). (https://www.sciencedirect.com/science/article/abs/pii/S1071909115000224).

We can also view sleep as a being sort of bank, where hours are either deposited or withdrawn. Overtime, if withdrawals exceed deposits, the balance will need to be topped up. To stay happy and healthy, we need sufficient zzz’s. See guidelines for how many hours of sleep are needed at each age here: https://www.medicinenet.com/how_much_sleep_do_you_need_by_age/article.htm.

As we age, sleep patterns change, though sleep is still crucial for optimal health. The average 70 year old needs 7hrs of sleep and though does not have the same energy requirements as a younger person, nor are the cells of the body renewing at the same rate - sleep remains key and becomes increasingly diurnal as well as nocturnal.

Sleep tips

Sleep is a core activity, so making sure we dedicate some energy towards making it as blissful a possible is grand.

Here are a few tips on making your bedroom your sanctuary and encouraging a blissful nights’ sleep.

1. First of all, lighting. As we have established, the darker the room the better for our brain, so taking steps to create a pitch black space is well worth the effort. A good eye mask and/or black out blinds do the job. Unless you live in a quiet, rural area, you may need ear plugs too.

2. Next reduce or eliminate electronics from the bedroom. This means placing mobile phones outside the bedroom and creating a sanctuary of rest and a digital, blue-light free zone.

3. During the daytime, open windows to oxygenate the room and keeping the window slightly ajar at night is even better. The brain needs two things really: oxygen and glucose - so less of the sugar at night obviously, and ensuring our sleeping space is well ventilated, where air is constantly circulating, is really beneficial.

4. A good mattress is a must to support the body and ensure you are sleeping comfortably. We recommend natural organic latex mattresses, such as Heveya (https://www.heveya.com/products/organic-latex-mattress), which provide proper support and temperature control, while being free of chemicals and other problematic materials.

5. Next of course, make your space warm, cosy and inviting. A down or better still wool duvet, is cool in summer and warm in winter. We love Fogarty’s All Seasons Wool Duvet. (https://www.dunelm.com/product/fogarty-wool-all-seasons-duvet-1000077078).

Natural candles create a soft and nourishing atmosphere and keeping a nice pillow mist (https://www.norfolknaturalliving.com/products/pillow-mist ) to hand, with soothing natural fragrance helps to provide a nice aroma and relaxation before bed.

6. Try not to eat a heavy meal after 7pm, even better stick to a light protein and vegetable meal in the evenings. And of course, limit sugary or starchy foods that provide an energy hit when you are trying to wind down.

7. Try to keep to a regular bedtime, say from 10.30pm-11pm each night. The body and brain love a routine and as we have established, sleep is a rhythmic and circadian activity.

8. A little reading or breath work can help you switch off and ensure you are comfortably on your way to dropping off.

9. If you are suffering from bouts of insomnia, the first thing to do is check your vitamin and mineral levels, for example, iron, calcium, zinc and magnesium, as well as hormone levels, for example, oestrogren levels, which affect the production of melatonin. Melatonin is a hormone that is secreted by the pineal gland at night and is known to regulate sleep wake cycles.

Melatonin is a naturally occurring substance in plants and animals, and excellent sources of melatonin are nuts, mushrooms, oatmeal, eggs and fish. https://pubmed.ncbi.nlm.nih.gov/28387721/. Iron is also a big one. Iron deficiency (anaemia) can cause insomnia, low energy and low mood. Ensure your diet is providing the nutrition your body needs in order to synthesise the molecules needed for the onset of restful sleep.

Sleep disturbances and sleep deprivation impact our hormone balance, nervous system functioning and ultimately our immunity to disease, so understanding what makes us want to sleep and supporting healthy sleep patterns is key for our wellbeing and longevity.

 For more facts and tips about sleep, drop us a line here. We are more than happy to oblige.

Well, good night! and sweet dreams.

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