Nighttime brain cleaning and headaches

The lymphatic system

This important waste clearance task is handled by our lymphatic system. It consists of a network of fine-walled vessels that transport a yellowish-white fluid, known as "lymph," into the venous system. This lymph fluid helps to flush dead cells, proteins, foreign substances, bacteria, fats and metabolic end products out of the body. The lymphatic system extends throughout almost the entire body – but interestingly, it does not reach the brain. Instead, it ends at the meninges (the membranes enveloping the brain and spinal cord).

How does our brain clean itself?

The absence of lymphatic vessels in the brain has puzzled researchers for generations. The brain, after all, is a hotbed of metabolic activity, producing a significant amount of waste. And nerve cells (neurons) are notoriously sensitive to accumulated toxins and waste. Scientists have long suspected that there must be a waste disposal mechanism within the brain itself.

Until a decade ago, however, there were no clues about what these structures might be like and how they might work. Many experts assumed that the brain’s cells handled waste clearance on their own.

This view changed fundamentally in 2012. That’s when a team of researchers led by Danish scientist Maiken Nedergaard discovered a mechanism in the brain’s glial cells, which they named the “glymphatic system” (a portmanteau of "glia" and "lymphatic system"). They were the first to describe these structures and their functions.

An exciting discovery: the glymphatic system

The system operates similarly to a “pipe-in-pipe" setup seen in technical applications such as water or heating installations.

The inner pipe consists of small arterial blood vessels that permeate the brain. An outer layer of specialized nerve cells (glial cells) and their projections surrounds these vessels like a second skin. In this outer space flows a brain fluid composed of various elements. This fluid crosses into the brain tissue, picking up both dissolved and undissolved substances. The flow is driven by pulse waves from the arterial walls. Once the fluid reaches tiny venous vessels, it transports waste to larger veins and releases its load into the body's lymphatic vessels. The waste flow from the brain unites with the body's lymphatic system at this point. The waste is eventually eliminated through the liver and kidneys.

This process provides the brain with a clearance system akin to the lymphatic system serving the rest of the body. The efficiency of this system is impressive: recent estimates suggest that the brain produces about seven grams of waste per day – approximately two and a half kilograms per year, nearly double the brain’s mass. The waste disposal system usually works just fine.

But what happens when the process is disrupted, ineffective or temporarily stops working?

Cleaning only happens at night

Waste disposal in the body occurs at night, making deep sleep essential for the nervous system’s proper functioning. According to current research, poor sleep might contribute to a range of neurological disorders. Studies in animals have shown that sleep deprivation leads to a greater accumulation of harmful protein particles.

The glymphatic system and headaches

There is a close relationship between sleep and headaches. According to a Spanish survey, about half of people who get tension headaches or migraines also experience sleep disorders. Many headache sufferers notice the impact of a poor night’s sleep the next day, as headaches often follow a bad night.

Another finding suggests a link between brain cleaning and migraines. Before a migraine attack, especially with aura, a wave of neural excitation spreads through the brain. During this state, the fluid spaces in the glymphatic system may close for several minutes. This could halt the movement of brain fluid needed to clear toxins. Toxins are not cleared during this time, which can be very dangers for neurons. The result is damage to nerve cells, which can trigger a migraine attack.

Chronic migraine and medication overuse: the glymphatic connection

A 2024 study from Taiwan used advanced imaging techniques to better understand the role of the glymphatic system in migraines and medication-overuse headaches. Researchers examined the structures and functions of the glymphatic system and the draining lymphatic vessels in the meninges, where (as stated above) the brain's cleaning flow meets the body's lymphatic system. They found reduced functionality in the areas where these systems join in patients with chronic migraines, more so than in those with episodic migraines. This impairment was most pronounced in people who had developed medication-overuse headaches in addition to chronic migraines. These findings align with observations that the impact of migraines on brain cleansing worsens with the frequency of attacks.

There was also a correlation between headache intensity, the degree of migraine-related disability, and sleep quality. The study also suggested that high usage of headache medications might interfere with brain cleaning.

Proven strategies for prevention and treatment

These insights raise new questions. For instance, could treating sleep disorders improve brain cleaning and in that way help prevent headaches? Further research might uncover additional treatment approaches to support the work of the glymphatic system. In the quest for effective and sustainable headache prevention, the research on the brain's ingenious cleaning mechanism supports the idea that people with headaches should aim for regular, restorative sleep.