What were you thinking about just now? Maybe you were caught in the midst of a continuous stream of thoughts. That is how we often talk about our waking lives – and it’s the way our conscious minds are often depicted in novels and discussed in philosophy. Yet, for some people, and maybe this includes you, that stream is interspersed with lulls, moments where the flow suddenly stops and the mind is left empty. If so, the chances are your honest answer to what you were thinking about just now could be: nothing.
If you have these experiences of mental emptiness, you will know what I am referring to. If you haven’t experienced them, maybe you are surprised to hear that they exist. Yet they do and, for anyone intrigued by the nature of consciousness, they are a fascinating, mysterious phenomenon that challenges conventional approaches to the subject.
Until recently, scientists approached the study of consciousness in two main ways: ‘being conscious’ and ‘being conscious of’. The first approach deals with that fact that, while we are conscious beings, we are not always conscious. For instance, when we fall into dreamless sleep, or when we are anaesthetised, our consciousness fades and then returns. The second approach is about the content of consciousness – the fact that, while we can be conscious of many things, we are certainly not conscious of everything.
Implied in this established dichotomy is the assumption that being conscious means being conscious of something. Our consciousness roams, it can be focused on the here and now, or maybe the there and then, but it is always focused on something. Yet the experience of lulls in consciousness content challenges this assumption. When you are asked the sempiternal question ‘What are you thinking about?’ and the only response that comes to your mind is ‘Nothing,’ it suggests that, while you were conscious, you weren’t conscious of anything. In a recent review, my colleagues – two neuroscientists (Athena Demertzi and Antoine Lutz) and a philosopher (Jennifer Windt) – and I defined these moments as ‘mind blanking’.
These gaps in the stream of thoughts are quite puzzling, as they suggest that consciousness is punctuated by ellipses that often go unnoticed. If this is true, then the idea that conscious life reflects a continuous flow of experiences might actually be an illusion.
To find out more about mind blanking, I’ve been taking a simple approach – interrupting research volunteers at random moments during a sustained concentration task (they have to press a button each time a digit appears on screen, but watch out for specific digits that don’t require a response). At these moments, I ask them to indicate the content of their thoughts, or absence thereof, at that moment – a method called ‘experience sampling’. When they’re offered the option to report ‘thinking about nothing’ alongside alternative options such as thinking about the task or mind wandering, participants typically choose the mind blanking option about 15 per cent of the time, which I found surprisingly high.
If you’re sceptical, you might naturally ask: how can we be sure that the participants’ minds really were blank? This is a fair question, and of course the objective study of consciousness is always somewhat limited by the fact its target phenomenon is subjective experience. However, there are ways we can scrutinise people’s subjective reports of their mind blanking – by examining their behaviour and their brain activity during these moments.
Mind blanking reflects a disruption of the stream of consciousness, similar to what occurs at sleep onset
In both these respects, mind blanking stands out. From a behavioural perspective, we find that, when someone’s mind is blank, they are also slower to respond (to the prompt to describe the content of their thoughts). This response profile contrasts with when they are task-focused, but also with mind wandering, during which they tend to respond more quickly than usual, presumably because they are less distracted by the task itself.
Brain activity is also distinct during mind blanking. Using fMRI to record the degree of activation and dialogue between brain regions, in a 2022 study, Demertzi and colleagues showed that mind blanking is associated with a specific pattern of hyperconnectivity. Instead of specific brain areas being in communication with certain other areas, there is a widespread, uniform increase in communication across the brain.
You might think that a more highly connected brain is a good thing. Up to a certain point, this is true, but hyperconnectivity can be detrimental for consciousness because it reflects a lack of functional organisation. Hyperconnectivity is a key feature of epileptic seizures, and it is also observed at sleep onset, when consciousness fades away.
In fact, mind blanking mirrors sleepiness in other ways. It is associated with signs of decreased physiological arousal, such as smaller pupils of the eye and a slower heartbeat. And in my own work that involved measuring the brain’s electrical activity, my team showed that, during mind blanking, your brain will tend to produce the slow waves of electrical activity that are reminiscent of sleep. This suggests that mind blanking reflects a disruption of the stream of consciousness, similar to the one that takes place at sleep onset. If confirmed, this could have significant implications. For example, it would mean that mind blanking should be particularly prevalent in individuals who are sleep deprived (and that’s exactly what Demertzi is finding in her research).
The idea that mind blanking might reflect a kind of sleep-like interruption of waking consciousness also helps make sense of the observation, by another research team, that adults and children with ADHD report mind blanking more frequently. At first, this may seem at odds with the idea that someone with ADHD has a mind that is too full rather than empty. However, both adults and children with ADHD frequently experience sleep difficulties, which could cause sleep-like intrusions into their waking lives. Indeed, I recently published a preprint that found the instances of mind blanking among participants with ADHD tended to co-occur with slow-wave activity in the brain, indicative of sleep intrusions within their wakefulness.
Despite these promising recent developments, the research on mind blanking is still in its early stages of trials and errors. A central question is how to grasp such an evanescent phenomenon. Mind blanking is so brief, it is usually over by the time we notice it, if ever. Catching mind blanks at random, using the experience-sampling approach, is like shooting in the dark. Maybe there is another way?
So far, I’ve been describing what Windt calls the ‘wild type’ of mind blanking: the mind blanks that occur spontaneously, perhaps because of tiredness. She contrasts these with the ‘cultivated type’: the way some meditative practices such as nirodha-samāpatti teach followers how to empty their mind intentionally, to reach a state of awareness unencumbered with an uncontrolled stream of thoughts.
Maybe mind blanking allows reparative functions to be carried out during wakefulness
Studying these states could help shed further light on the precise nature of wild mind blanking. For example, if research confirms that, during certain meditative states, people maintain self-awareness or a sense of time passing even with an empty mind, this would show that an absence of mental content doesn’t necessarily mean an absence of consciousness. In other words, when your mind goes blank of its own accord, ‘you’ are still consciously aware, even if you are not conscious of anything.
A key unresolved question is whether spontaneous mind blanking serves a function. When your mind goes blank momentarily, does this simply reflect a failure of your brain to maintain a level of arousal sufficient to keep your stream of consciousness flowing? Or, on the contrary, are your mind blanks a useful feature of your mental life that enable or prevent some other specific, beneficial process? Or maybe it is neither of those, but just an epiphenomenon without purpose or consequences.
The relationship between mind blanking and sleep intrusions might offer some clues. Sleep intrusions take the form of slow-wave brain activity, which is a key hallmark of sleep, directly implementing the restorative function of sleep. During sleep, slow waves rebalance synaptic weights, restore metabolic resources, help evacuate metabolic waste, and so on. When we are not doing anything particularly interesting, maybe mind blanking allows these reparative functions to be carried out during wakefulness. To find out if this is the case will require a combination of complex techniques to monitor not only neural activity but also brain metabolism and will likely keep me busy for the coming years.
If you occasionally find yourself blanking out, I hope you will be reassured to know that you are not alone, and that it often simply reflects a touch of fatigue. The next time it happens, you might also stop to marvel at the implications of your experience. Mind blanking challenges the long-held scientific assumption that being conscious means being conscious of something. It also invites us to reconsider what it means to be conscious, and highlights the diversity and dynamism of our mental life. Mind blanking may appear as a mere crack on the surface of consciousness, something subtle and easy to dismiss, yet this modest fissure conceals unexpected wonders.
