Science widely acknowledges the healing effects of sleep. It restores every part of the body. It can even help alleviate neuropsychiatric conditions stemming from chronic stress. Studies show that sleep heals the mind by increasing the production of brain-derived neurotrophic factor (BDNF). BDNF induces brain cells to multiply or re-organize around unused neural networks.

In this article, we talk about the basic science of sleep. We also explain how good sleep increases BDNF levels and the evidence for its role in maintaining and restoring brain health.

What Is Sleep, and Why Do You Need It?

Sleep is unconsciousness from which you can wake up when stimulated. It is characterized by rhythmicity and balance.

Sleep’s rhythmicity is controlled by the circadian rhythm, which relies on light perception. At daytime, light enters your brain through the retinas and optic nerves. Some of the neural pathways connected to the optic nerves stimulate your Reticular Activating System (RAS), waking up the rest of your brain. At night, the RAS rests while other brain regions take over and start to facilitate sleep. 

On the other hand, sleep balance or “sleep homeostasis” is the tendency to sleep more when a person stays awake longer than usual. It causes rebound sleep.

Sleep is divided into two major stages: non-REM (NREM) and REM sleep. 

During NREM sleep, both your brain and body are relaxed. It has the following sub-stages:

• NREM1 is where very light sleep occurs. You spend only a few minutes in this stage.

• NREM2 is the stage where your brain goes into a deeper sleep. Your heart rate and breathing slow down further, and your body temperature slightly falls. You spend most of your sleep hours in NREM2.

• NREM3 is the most restful sleep stage. Here, your brain secretes growth hormone, and growth and repair mechanisms peak. You can have dreams during NREM3, but you will not remember them when you wake up.

By comparison, REM sleep is associated with active dreaming. Your brain is fired up, but it paralyzes most of your body to keep you from acting your dreams out. You also experience rapid eye movement (REM) at this time, hence the name. You can easily recall your REM dreams.

It is normal for you to sleep less as you grow older. You may even have fewer hours of good-quality sleep as you spend increasingly less time in NREM3 and more time in NREM2. On the other hand, sleep disturbance can cut NREM3 and REM short without compensation during the same sleep-wake cycle. These changes affect BDNF production and brain function differently.

 You need sleep because it has vital functions in your body. It helps to:

• Conserve your energy.
• Reverse oxidative stress in your brain so it can regain its speed and clarity.
• Restore your muscles’ strength.
• Relax your other organs so they can recover their efficiency. 
• Deep sleep promotes growth hormone secretion. This contributes to the healing of injuries and overall growth.

When your body cannot do these things, you become vulnerable to illness, inflammation and burnout. Sleep disturbance results from chronic physical or mental stress, though it can also be a symptom of mental health problems.

How Does Sleeping More Heal Your Mind?

Evidence that BDNF could mediate the therapeutic effects of sleep on the brain is growing. Below, we summarize what is known today about the relationship between sleep, BDNF and mental health enhancement.

Acute and Chronic Forms of Sleep Deprivation Have Different Effects on Serum BDNF Level

Serum BDNF is an indirect measure of the brain’s BDNF level. Research shows that acute stress increases serum BDNF. Meanwhile, chronic stress reduces it by increasing blood cortisol.

How does this relate to sleep?

Serum BDNF rises after a person experiences some form of acute stress, such as a short period of fasting or aerobic exercise. Similarly, it has been found that people who skip a day of sleep have higher serum BDNF concentration the next day. Rebound REM sleep and greater growth hormone secretion are also observed in the next sleep-wake cycle. 

In contrast, depressed patients and people with insomnia have lower serum BDNF. Habitual sleep deprivation subjects the body to chronic stress.

Chronic Stress Is Linked to Poor Sleep, Low BDNF, Cognitive Dysfunction and Depressive Brain Changes

People experiencing chronic stress have elevated blood cortisol, low blood BDNF, sleep problems and poor cognitive function. They are also at risk for developing an anxiety or mood disorder later on. Research on the effects of stress on the human brain is limited, although the findings among depressed patients are rather revealing.

Untreated depression is marked by a small hippocampus and thinning of the prefrontal cortex on MRI. Cognitive dysfunction, demotivation, sleep disturbance and low serum BDNF are common among patients. Meanwhile, postmortem hippocampal BDNF is higher among depressed patients on therapy.

BDNF Level is a Predictor of Sleep Duration and Quality 

Sleep disorders variably affect morning serum BDNF concentration. However, it has been found that people with insomnia tend to have lower morning serum BDNF. In contrast, those with narcolepsy usually have higher morning serum BDNF. This suggests that sleep duration may directly affect brain BDNF levels.

This trend may be explained by the positive feedback loop between serotonin and BDNF. Normally, your brain secretes serotonin right before you sleep, and this induces BDNF secretion. Conversely, BDNF raises serotonin levels. This mechanism helps prolong sleep.

Meanwhile, sleep studies also show that morning serum BDNF goes up when either NREM3 or REM gets longer. The body is most relaxed during these stages, so increasing BDNF levels may also be an indicator of restful sleep.

Circadian Rhythm Shifts Provide Quick Relief of Depressive Symptoms

Interventional research shows that BDNF may play a larger role in the evolution of depressive symptoms than previously thought. Conventional antidepressants take weeks to act, and their effects on sleep and cognitive function are also inconsistent. Meanwhile, experimental therapies like partial sleep deprivation (PSD) and ketamine infusion improve symptoms within hours.

The difference?

Conventional treatments target the neurotransmitters serotonin, norepinephrine and dopamine. They increase BDNF in the hippocampus, but that is now seen as merely an indirect antidepressant effect. Meanwhile, PSD and ketamine alter the circadian rhythm and increase BDNF directly, thus the rapid changes in the brain.

Immediate symptomatic relief is life-saving for depressed patients with suicidal tendencies. That is why other BDNF-focused antidepressants are in the pipeline. However, BDNF modulation is also currently being explored to treat other conditions affecting cognition and sleep, e. g. Alzheimer’s disease, burnout and insomnia.

Adaptive Brain Changes Result from Combining BDNF Action and Sleep 

Various factors influence daytime BDNF production. However, just like many substances in the body, it’s now known that this neurotrophin’s secretion also follows a diurnal pattern. This information is significant in light of the roles that BDNF and sleep play in neuroplasticity.

Your brain’s plasticity allows you to learn from new experiences. Adaptive changes occur because new brain cells grow, especially in the hippocampus, and neuronal connections adjust. BDNF stimulates these processes. It acts when you are wide awake and exposed to your experiences. However, only when you sleep do the changes become permanent.

You can observe this among students taking a test. Those who have good sleep habits after studying tend to score better than those who sleep poorly. Memory consolidation is attributed mostly to REM sleep.

Neuroplasticity is also the reason why physical therapy can rehabilitate people with neuronal injury, or why psychotherapy works for stress-related conditions. It is usually hard to replace a damaged neuron. However, by adapting to new habits and thought patterns, intact nerves can rewire, allowing the nervous system to reprogram.   

Stress can blur your mental focus and derail you from your goals. The next time you feel stressed, do yourself a favor—step back and get a good night’s sleep. And help yourself to natural brain-detoxing fixes like eating healthfully, taking BDNF-stimulating vitamins and going for a nature walk. Taking care of your mind is not only okay but imperative to your overall health.

Conclusion

The health benefits of restful sleep are well-established. However, the mechanisms that allow it to restore brain health are only now being understood. Recent studies show that BDNF mediates many of sleep’s brain-healing effects, and that normalizing BDNF levels improves brain function. This information paves the way to safer and more effective mental health interventions.

References:

1. https://doi.org/10.1073/pnas.2008004117
2. https://doi.org/10.1677/joe-07-0376
3. Benca, R. M., Cirelli, C., & Tononi, G. (2017). Basic Science of Sleep. In Sadock, B. J., Sadock, V. A. & Ruiz, P. (Eds.). Kaplan and Sadock’s Comprehensive Textbook of Psychiatry. (10th ed.), pp. 339 – 353. Wolters Kluwer Health.
4. https://dx.doi.org/10.1037%2Fneu0000396 
5. https://doi.org/10.1111/jsr.12577
6. https://doi.org/10.1016/j.cobeha.2019.12.008
7. https://doi.org/10.1371/journal.pone.0076050
8. https://www.clinicalkey.com/#!/content/book/3-s2.0-B9780323597128000606?scrollTo=%23hl0000055