Subsequent research has generally shown that the circulation of cerebrospinal fluid through the glymphatic system:

• is much higher during sleep and is
• suppressed by wakefulness, particularly in response to noradrenaline, a hormone and neurotransmitter that is associated with the sympathetic nervous system.
• is suppressed by sleep deprivation
• is reduced in older people
• is reduced in people with neurodegenerative diseases, that are characterised by the build up of protein waste such as amyloid-ß, tau and synuclein, e.g. Alzheimer's.

Is this one of the reasons that we, and all animals, need to sleep?

And one reason why chronic stress is so debilitating?

Certainly, helping our glymphatic system to work as efficiently as possible can only promote the best health in our main control centre, our brain.

Optimising the cleansing of our brain

• Sleep
• promote good sleep habits
• no search engines or social media scrolling for at least an hour prior to bed
• cool room, comfortable bedding
• warm shower or bath before bed (not too hot, we need to be a little cooler to drop off to sleep
• use a body brush or shower spray to gently stroke up your legs and arms towards your body to aid relaxation of your nervous system and promote lymphatic drainage
• visualisation relaxation e.g. visualise your Tai Chi routine in your mind
• Lymphatic drainage,
• good breathing techniques
• gentle movement 
• incorporate a simple lymphatic drainage routine into your nightly ritual
• Stress reduction
• noradrenaline impedes the glymphatic system and chronic stress is particularly hard on your body.
• Meditation or movement therapy
• Tai Chi is a wonderful means to promote the enhancement of your natural electromagnetic field, which has a balancing effect on your whole body and mind.
• Optimise
• nutrition
• hydration
• exercise
• recuperation
• Cranial osteopathy
• may help to promote good CSF circulation

• Eat enough ◊ Move enough ◊ Rest enough ◊ Live enough = play, party, potter, pamper, progress...
  

It's all about achieving a healthy balance:

• For example we actually need noradrenaline for good focus and attention (it is low in ADHD sufferers), as well as for effective use of our muscles when exercising.

So stress can be healthy, but everyone is different!

• Do something exciting, scary, fun… for you, every day.

Relaxation is healthy, but everyone is different!

• Do something calming, relaxing, soothing… for you, every day. 

Moderation in everything.

The circulation of CSF around the brain

Image: CSF Circulation. OpenStax, CC BY 4.0, via Wikimedia Commons

The brain is covered with three layers of coverings, the meninges, that help protect it. The outer most layer is connected to the bony skull and is called the dura mater. It is lined by the arachnoid mater, which has a web-like consistency that helps support the blood vessels that surround the brain. The entire undulating surface of the brain is covered in a thin covering called the pia mater - the deepest of the three meningeal coverings of the brain. Between the arachnoid mater and the pia mater is the subarachnoid space.

The subarachnoid space carries the arteries and veins carrying blood to and from the brain substance and is also filled with cerebrospinal fluid (CSF). The CSF is produced in reservoirs, called ventricles, within the brain and flows continuously around the brain and spinal cord. It helps to support the brain - the brain literally floats within the skull, and it assists with fluid and electrolyte balance within the brain tissues.

The Blood-Brain Barrier

Arteries and veins penetrate deep into the brain in order to supply the billions of neurons it contains with oxygen and vital nutrients including glucose, vitamins and minerals. 

The pia mater that tightly covers the surface of the brain, also coats these penetrating arteries and veins forming a 'perivascular space' that is continuous with the subarachnoid space and that is also filled with cerebrospinal fluid.

The csf-filled perivascular space continues along the blood vessels, but as the vessels infiltrate into deeper structures they branch and become finer and finer, and the pia mater surrounding them gradually becomes thinner. Finally at the level of capillaries the pia is no longer present. With the absence of the pia mater in this level there is a need for a barrier that restricts the passage of molecules from the blood to the nervous tissue. This is achieved in two ways:

1. The capillaries within the brain tisssue are formed from highly specialised endothelial cells that have much tighter 'pores' that the cells that form the capillaries in the rest of the body. These pores tightly limit the type of substances that can enter the extracellular spaces around the neurons of the brain substance.
2. since they are no longer separated from the brain by the pia mater, they are instead wrapped by astrocytes, which form a membrane around the vessel wall with the use of their end-plate processes. Astrocytes are non-nerve cells that live amongst the neurons of the brain, playing a varied supporting role.

The astrocyte end-plates also restrict entry of many molecules and ions, and the combination of the specialised capillary walls and the astrocyte end-plate covering forms the 'blood-brain barrier'.

The Glymphatic System

As the central nervous system is so well protected by the blood-brain barrier, it used to be thought that larger protein waste products from the cells of the brain were degraded locally by the glial cells that support the neurons, the 'main workers' of the brain. This was in contrast to the cells and organs of the rest of the body, much of whose waste is transported away by the lymphatic system.

However, in 2012, Maiken Nedergaard and colleagues, working at the University of Rochester and University of Copenhagen, discovered that the astrocyte membranes of the blood-brain barrier contain large protein channels that allow water from the cerebrospinal fluid to flow into the extracellular (interstitial) fluid that bathes the neurons that make up the substance of the brain.

Image: Glymphatic clearance. Neuroscience: Exploring the brain, 5th ed. 2025

This fluid washes the neurons of the brain and is then collected again in the perivascular space that surrounds the veins

• so the perivascular space around the venous capillaries acts in exactly the same way that the lymph vessels of the body collect waste lymph fluids (see box below).

From the perivascular space around the collecting veins, it is drained back into the cerebrospinal fluid of the subarachnoid space, but is kept separate by a membrane (the subarachnoid lymphatic-like membrane, or SLYM) before finally draining into the body’s lymphatic system, which collects debris and toxic metabolites from all the cells in our bodies.

Nedergaard called this novel brain-washing machine the glial-lymphatic, or glymphatic system.

Lymphatic system of the body

The lymphatics of the body collect waste fluids that can't get back into the blood capillaries

• some small proteins and particulate can't easily diffuse back into the high-pressure environment of a blood capillary
• if they stayed there, they would increase the osmotic pressure of the tissue, trapping even more water and causing massive swelling (oedema)
• this is a relatively common problem when the lymphatic system doesn't function effectively e.g. after breast cancer surgery to remove axillary lymph nodes

The lymphatic system is a very low-pressure environment, making it the path of least resistance for excess fluid so it can be filtered by lymph nodes and eventually dumped back into the veins near the heart.

• this also acts as  a security system. By forcing a portion of the interstitial fluid through the lymphatic system, your body ensures that tissue fluid is constantly being sampled by your immune cells in the lymph nodes.