Why does sleep deprivation have so many negative effects, ranging from irritability and the inability to concentrate to seizures, dementia and, death? Researchers studying waking and sleeping mice may have found the answer. Maiken Nedergaard of the University of Rochester Medical Center in New York and her colleagues have discovered that during sleep, the space between brain cells increases, so that fluid containing toxins can flow through these spaces. During sleep, toxins are removed from the brain.
In a study published in Science, the researchers looked at the glymphatic system, a pathway for cerebrospinal fluid (CSF). Waste from the central nervous system (CNS) passes through the glymphatic system, which plays the same role in the CNS as the lymphatic system does in other parts of the body.
Nedergaard’s team, who discovered the glymphatic system, found that brain cells called glia control the flow of CSF through cells. Because moving CSF takes energy, the team thought it wouldn’t be possible for the brain to transport CSF and process sensory information at the same time.
To test their hypothesis, they injected dye into the CSF of waking and unconscious mice. They found that when the mice were awake, the CSF hardly moved. However, when the mice were asleep or anesthetized, the CSF flowed rapidly.
When the researchers measured the spaces between brain cells, they found that it increased from 14% of brain volume when the mice were week to 23% of brain volume when they were asleep or anesthetized. When the mice were awake, CSF only flowed on the surface of the brain, but when they were awake, it flowed through the brain’s deep tissues.
The team was able to increase the space between brain cells by injecting waking mice with drugs that block noradrenaline, and so induce unconsciousness. This showed that the sleep-wake state itself, rather than the circadian cycle, was controlling the amount of space.
Because neurodegenerative conditions like Alzheimer’s disease are associated with the buildup of toxins in the brain, the researchers examined how sleep, or the lack of it, could affect such buildup. They injected mice with beta amyloid, a protein that builds up in the brains of people with Alzheimer’s. They discovered that the beta amyloid cleared from the brain twice as quickly when the mice were asleep as when they were awake.
Although this research explains one way that sleep can is good for us, it does not necessarily explain why sleep evolved in the first place. Sleep has many other benefits. During deep NREM sleep, for example, your immune system is strengthened and damaged tissues are repaired, while memories are consolidated during REM sleep. Sleep might have evolved to enable us to conserve energy or to keep us from moving and so avoid the attention of predators.
Original research: Xie, L., Kang, H., Xu, Q., Chen, M. J., Liao, Y., Thiyagarajan, M., … & Nedergaard, M. (2013). Sleep Drives Metabolite Clearance from the Adult Brain. Science, 342(6156), 373-377.
The ocean is the source of life on Earth, and odd, mysterious creatures still live in its depths. In a dream, the ocean can represent the basic, primitive emotions that lurk inside the unconscious.
Ocean dreams are often about strong emotions, like love, contentment, fear and anger – emotions that we experience fully even when we are very young and haven’t yet done much logical or rational thinking. In a dream about an ocean, these feelings come to the fore.
The condition of the ocean in your dream is a sign of how you truly feel. A calm ocean is a sign of inner calmness, while a stormy turbulent ocean means that something in your life is troubling you. Regardless of how calm the ocean may seem, ocean waves are always moving, just as our lives are always changing, although some changes are easier to handle than others are.
When you wade in the ocean, you leave the stability of the shore and find yourself amid the ever changing waves, so wading in a dream can mean that you feel confident that you can handle an uncertain situation. However, you are still cautious.
A dream that you are swimming in the ocean can signify you are ready to involve yourself fully in a new endeavor. This can also be a sign that you are getting in touch with your emotions. However, you may be making yourself vulnerable.
If you dive into the ocean, your dream could be saying that you are ready to “dive into” a new project. You are full of confidence and ready to take on whatever life brings you.
Are you taking a voyage in a ship across the ocean in your dream? Traveling in a dream is usually a symbol of your journey toward a goal or your journey in life, so this dream is about the emotions you experience as your circumstances change. Don’t be surprised to see exciting, possibly even terrifying, things during your dream journey. Experiencing new things and moving on to new stages in life can be frightening, but also exhilarating.
Is the ship sinking? This is a sign that you are worried that your plans will fail. The important thing about such a dream is how you react. Do you run around in a panic, worried that you are going to drown, or do you take charge, guiding the other passengers to lifeboats and making sure everyone is calm and safe? This is a sign of how you might react to the difficult situations that occur in your passage through life. If you panic in your dream, it is a sign that you tend to allow your emotions to take control when things get tough. Try to stay calm and allow reason as well as intuition to guide you during difficult times.