London in your head

While half of London is wondering whether the bin collection will be on time, I, SherlockMS, self-appointed Chief Inspector for Cerebral Affairs, am occupied with a more elegant question: Who actually takes out the brain’s rubbish? 🧠🚮

That is precisely the topic of a recent review in Neuron by the pioneering and legendary scientist and researcher J. Kipnis with the fitting title “Resolving the mysteries of brain clearance and immune surveillance”, a piece of work that essentially shows that our brain secretly has its own sewers, street cleaning and customs. And yes: neurology managed to overlook this for an astonishingly long time.

🏙️ The brain as a city

Imagine your brain as a big city:

• Neurons = flats, offices, pubs
• Glial cells = caretakers, electricians, cleaners
• Blood vessels = roads, bridges, ring roads
• CSF (cerebrospinal fluid) = a mix of water supply, street cleaning and waste system

For years we were told the brain was “special”: hardly any lymphatic vessels, very little immune system, everything hermetically sealed, basically an elite gated community. Sounds fancy, but it’s about as plausible as a London without sewage pipes.

In reality, this is what happens:

1. Influx 🚰

Fresh cerebrospinal fluid flows from outside into the brain along the arteries, in narrow tunnels that wrap around the vessels: the peri-arterial spaces. Think of it like water being pushed through back alleys deep into a residential area.

2. Through-flow 🧽

In the tissue, this fluid spreads between the cells and picks up rubbish: protein leftovers, metabolic by-products, little toxic molecules. Picture a combination of cleaning crew, mop and robot vacuum.

3. Outflow 🚿

The “used” fluid then leaves the brain via several routes: along veins, along nerves, through the meninges and finally into lymphatic vessels that drain into lymph nodes in the neck. There, the immune system inspects the contents like parcels at customs.

This interplay between CSF flow and glial cells is called the glymphatic system. A slightly clunky term for the simple fact that the brain does tidy up, just more elegantly than your dishwasher.

😴 Night shift upstairs – why sleep is brain hygiene

Here comes the bit that makes all the “I do fine on four hours of sleep” people slightly nervous.

During sleep, the following happens in your head:

• The blood vessels in the brain carry out slow, rhythmic widening and narrowing – vasomotion. It’s like a slow pump pushing cerebrospinal fluid through the perivascular “lanes”. 
• The space between the cells becomes a little wider, so the fluid can flow more easily. Less congestion, more throughput.
• In experiments, tracers move through the brain much faster during sleep; waste products are cleared more quickly than when we’re awake.

In humans, modern imaging techniques show huge CSF waves during deep sleep, synchronised with slow brain activity patterns. That’s not esotericism, that’s biophysics.

In everyday language:

At night your brain switches on dishwasher, hoover and drain cleaner all at once.

Good sleep = professional house-cleaning for your brain.
Chronic sleep deprivation = the bin lorry hasn’t come for weeks.

🛂 Brain customs – how the immune system reads along

The rubbish is not just dumped into nothingness. The brain’s drainage routes are cleverly wired into immune surveillance.

On its way out, the CSF stream passes several checkpoints:

• In the meninges sit immune cells that take up particles and protein fragments directly from the outgoing fluid – like security staff doing random checks.
• In the dura, the tough outer meningeal layer, there are lymphatic vessels that carry the cargo towards the cervical lymph nodes.
• In the lymph nodes, everything is analysed immunologically: Is this just normal brain activity, or is something suspicious going on?

You can imagine it as a courier service that delivers small daily samples from your brain to a very strict customs office.

If everything looks normal, it’s waved through.
If something seems off, immune responses can be ramped up or altered.

So waste clearance and immune surveillance are not two separate worlds – they’re two sides of the same system. The brain doesn’t just flush away rubbish; it sends status reports to the immune system at the same time.

🧓 When the pipes age – and why that matters for MS

Of course, such systems age. Pipes stiffen, pumping movements weaken, lymphatic drainage slows down.

There is growing discussion about how disturbances in brain clearance and lymphatic outflow may be linked to various diseases:

• In neurodegenerative diseases like Alzheimer’s, rubbish accumulates in the brain, and at the same time there are hints of disrupted fluid pathways.
• In autoimmune processes – this is where I, SherlockMS, prick up my ears – it is crucial how brain proteins are presented to the immune system. If the “rubbish stream” is misrouted, T and B cells can learn the wrong targets.
• Also in tumours, trauma, and possibly psychiatric disorders: where clearance and surveillance are altered, pathology can lurk in poorly lit back alleys.

For multiple sclerosis the message is clear: Anyone who only stares at lesions on MRI misses the hydraulic and immunological town planning in the background. The way brain material is reported to lymph nodes and the immune system may help decide whether autoimmunity arises at all – and whether it becomes chronic.

🧹 The future of brain hygiene – more than “keep your brain fit”

What follows from all this? The outlook is fascinating:

• Therapies that improve CSF flow and glymphatic activity – through vascular dynamics, breathing patterns, body position, medication.
• Approaches that specifically target meningeal lymphatic vessels to modulate immune responses.
• Sleep no longer just as a lifestyle topic, but as a genuinely neuroprotective treatment goal: “sleep as medicine”, not just “sleep as nice-to-have”.

In other words: we’re moving from “there’s a lesion” to “how are flow, waste collection and border control organised in this brain…and what can we tweak?”

So I remain in my London flat, the real rubbish lorry rattling down the street outside, and I can’t help but smile.

The city down there needs multi-tonne lorries, containers, bins and half an army in hi-vis jackets to keep its waste under control.

Your brain, on the other hand, manages with pulsating vessels, clever fluid highways, nightly cleaning waves and built-in immune customs stations.

If that doesn’t impress you, feel free to keep arguing about residual waste and recycling bins.

I’ll focus on the truly exciting question: How do we keep the upstairs flat clean..in a way that gives diseases like MS less of a chance? 🧠✨

SherlockMS
Chief Officer for Brain Hygiene, London