Sleep and brain health: what we’re learning about the glymphatic system and brain health
For years, we thought that sleep was simply a necessary break between two periods of activity. Today, we are beginning to understand that it also plays a part in maintaining and balancing the brain.
What happens in the brain whilst we sleep?
We spend about a third of our lives asleep. And yet, few bodily functions have for so long been both so commonplace and, at the same time, so difficult to understand.
For centuries, we viewed sleep primarily through its most visible effects: resting, recharging our energy and starting afresh the next day. Sleep seemed like a basic necessity whose main function was to restore enough capacity for us to carry on.
That idea remains true.
What is changing is not the value of rest. What is changing is our understanding of everything that happens whilst we rest.
Contemporary neurology is beginning to describe sleep not as a temporary interruption of brain activity, but as a highly organised biological state during which processes essential to the functioning of the nervous system continue to take place. Memory consolidation, functional reorganisation, metabolic regulation and mechanisms that we are still investigating form part of a reality far more complex than we had imagined for decades.
This new perspective has brought a seemingly simple question to the fore.
Perhaps it is no longer just a question of how much we sleep.
Perhaps the question is now beginning to be: what does it really mean to sleep well?
Dr Alejandro Melcón Villalibre, a specialist in neurophysiology and head of the Neurological Sleep Disorders Unit at the Publio Cordón Memorial Hospital, explains that this shift is also clearly evident in clinical practice. For a long time, sleep was assessed almost exclusively in terms of quantity. Today, clinical experience requires us to broaden that perspective.
“There is a widespread belief that sleeping well simply means sleeping for long enough. In clinical practice, we see something different: people who apparently sleep for many hours yet still feel they are not getting proper rest, and others who maintain reasonable sleep schedules but suffer from specific sleep disturbances that ultimately affect their memory, attention or quality of life. Sleep has a qualitative dimension that often goes unnoticed.”
And perhaps that difference between sleeping and resting is precisely one of the reasons why sleep is becoming one of the most interesting fields in modern neurology.
The glymphatic system: the discovery that changed the way we study sleep
Although it accounts for approximately two per cent of body weight, the brain consumes around twenty per cent of the body’s energy. It remains extraordinarily active even whilst we sleep and relies on complex mechanisms to maintain balance in an environment that never completely stops functioning.
For decades, there was a question that was difficult to answer.
If the brain works so hard, how does it maintain that balance?
At the start of the last decade, a series of studies opened up a line of research that continues to transform this debate.
In 2012, a group led by Jeffrey Iliff described a functional pathway through which cerebrospinal fluid appeared to flow around certain vascular structures and facilitate exchange processes with brain tissue.
That proposal gave rise to the concept we now know as the glymphatic system.
It is worth pausing here.
The glymphatic system should not be interpreted as a brain-cleaning system, nor as a definitive explanation of how the brain works. It represents an active line of research that seeks to understand how certain fluid movements might play a part in maintaining the brain’s environment.
And it was precisely sleep that turned this hypothesis into one of the most stimulating fields of modern neuroscience.
The moment sleep ceased to be seen as inactivity
In 2013, researchers at the University of Rochester published one of the most influential papers in recent neuroscience.
In animal models, they observed that during sleep there was an increase in the exchange between cerebrospinal fluid and certain spaces within the brain tissue, and they described an approximate 60 per cent increase in extracellular space compared with the waking state.
The finding had a huge impact because it suggested something we had scarcely considered until then: that certain functions related to the balance of the brain’s internal environment might behave differently during sleep.
However, as Dr Melcón points out, translating these discoveries into clinical practice requires caution.
As with many promising lines of research, understanding a physiological mechanism does not mean that a diagnostic or preventive tool is immediately available.
“We are still a long way from using these mechanisms as direct tools for diagnosis or prevention. But they do help us to understand something important: sleep is not a passive state and probably has broader implications for brain function than we thought a few years ago.”
Perhaps that is the real change. Not having found definitive answers, but having begun to ask new questions.
Sleeping poorly does not always mean having insomnia
This shift in understanding is also changing clinical practice.
We now know that sleep-related problems do not always present themselves in an obvious way, nor do they stem from a single cause.
Some people find it difficult to fall asleep. Others sleep for a sufficient number of hours but feel that they have not had a restful night’s sleep. Some experience frequent awakenings. In other cases, respiratory disorders, neurological conditions or changes in the very architecture of sleep are involved.
According to data from the Spanish Society of Neurology, between 20% and 48% of the adult population report occasional difficulties sleeping, whilst approximately 10% to 15% suffer from persistent forms of insomnia.
In this context, Dr Melcón explains that one of the most common misconceptions is the assumption that sleeping and resting are necessarily one and the same thing.
In his practice, he notes, it is not uncommon to encounter patients who arrive convinced that their sleep is normal simply because they manage to sleep for a certain number of hours.
“When we look more closely, we find repeated awakenings, daytime sleepiness, a feeling that sleep is not restorative, or gradual changes in concentration and performance. Sleep can be disrupted in far more subtle ways than we usually realise.”
And that is precisely why certain situations warrant a more detailed assessment.
How we study sleep disorders today
One of the most significant advances in recent years is that sleep can now be studied in a way that would have been hard to imagine just a few decades ago.
It is no longer simply a matter of asking how many hours a person sleeps.
The focus is on understanding how sleep is organised, how the brain responds during the night, how breathing behaves, and whether there are any abnormalities that might explain certain symptoms.
That is why, explains Dr Melcón, a significant part of clinical work involves translating seemingly non-specific symptoms into specific questions.
Many people arrive expecting to find a single answer and discover that sleep is an extraordinarily complex function. Sometimes the aim is not to identify a specific condition, but to understand patterns, recognise modifiable factors and develop strategies to restore rest and quality of life.
At the Publio Cordón Memorial Hospital, we have the Neurological Sleep Disorders Unit, which forms part of the Neurology Department and is headed by Dr Alejandro Melcón Villalibre.
The unit has diagnostic tools such as a specialist sleep clinic, polysomnography, respiratory polygraphy and neurophysiological studies, which enable us to examine different aspects of sleep from a personalised perspective.
Because understanding sleep is not simply about sleeping more.
Sometimes it is about realising that what we have for years interpreted as tiredness might actually be worth investigating.
Sleep and brain health: what we know today and what we are still investigating
We are probably still a long way from fully understanding everything that happens whilst we sleep.
But perhaps one of the most interesting developments emerging from this new era in neurology is not the discovery of a new mechanism.
Perhaps it is the realisation that sleep was never merely a pause.
And that some of the brain’s most sophisticated functions seem to require precisely that time which, for so long, we mistook for inactivity.
The information contained in this article is for general information purposes only and is not a substitute for an individual medical assessment.
Frequently asked questions
Does sleeping well mean sleeping for many hours?
Not necessarily. Although the duration of sleep is important, we now know that the quality of rest also plays a key role. Getting enough hours of sleep does not always mean that the sleep is restorative. Frequent waking, a persistent feeling of tiredness, daytime drowsiness or difficulty concentrating may indicate that your sleep is not fulfilling its function properly.
What is the glymphatic system?
The glymphatic system is a line of research in neuroscience that studies how certain fluid movements within the brain might help maintain the balance of the brain’s environment. Research into this area has attracted particular interest because some studies suggest that certain processes related to this exchange may behave differently during sleep. Although it remains an active field of research, it is helping to broaden our understanding of the relationship between sleep and brain function.
When is it worth investigating sleep?
It may be useful to assess sleep when persistent symptoms arise, such as a feeling of not having had enough rest, frequent awakenings, daytime sleepiness, difficulty concentrating, changes in usual performance, or when rest no longer results in a feeling of recovery. Not all sleep problems manifest as insomnia, and in some cases, a specialist assessment can help to better understand what is happening.
How are sleep disorders assessed today?
The assessment of sleep begins with an individualised clinical evaluation and, depending on each situation, may be supplemented with specific tests. These include polysomnography, which analyses various physiological variables during sleep; respiratory polygraphy, which focuses on the study of specific sleep-related breathing disorders; and various neurophysiological studies that help to understand how sleep is organised and whether there are any abnormalities that might explain the symptoms.
The information in this article is provided for general awareness and does not replace an individualised medical assessment.
