My first memory is of my family moving house when I was 3 years old. I can picture the removal van at the gate with my brother in the front seat, and I remember worrying about how his pet rabbit would fare on the journey.
Before this moment, my autobiography is a blank page. At some point between my conception and that morning we moved house, I must have gained the ability to think, with an awareness of my body and its surroundings all knitted together into something we loosely call consciousness – but I have no idea when that occurred.
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Most parents would assume that their newborn is conscious from the moment they hold them in their arms, but how do we really know? It is a problem that has been troubling philosophers for decades. “There’s this general issue of, when did we begin? When did this stream of consciousness first emerge, if I can’t remember it?” says at Monash University, Australia.
The answers, however, haven’t been forthcoming, with some researchers claiming it is already present at birth and others arguing it arises after our first year or later. Now, improvements to infant brain imaging are bringing clarity to the debate – suggesting an early origin of consciousness, perhaps even emerging just before birth.
Besides helping us imagine what life is like during those first moments of infant awareness, these insights help us to understand what consciousness is. “If you know when consciousness emerges, you can know what type of brain structures are necessary and sufficient,” says , a bioethicist at New York University.
First, some definitions. The inner life that you are experiencing now as a waking adult is a fusion of many different elements, including a sense of self. This is often assessed through the mirror test. A parent may put a little mark on a baby’s nose, for instance, and place them in front of a shiny surface. If the child notices the mark and rubs it off, they have succeeded in recognising their own reflection – a sign that they have a sense of self.
Most babies fail this test, while toddlers between around 18 months and 2 years of age can generally identify the mark successfully. Clearly, some of the experiences of consciousness that we take for granted need time to develop, even after we have been born.
Core consciousness
Bayne and his colleagues are more interested in the origins of primary, or “core”, consciousness. They define this as a subjective perspective comprised of distinct experiences of phenomena such as the taste of coffee or the scent of lavender. Crucially, the contents of each conscious moment are integrated into a single experience. When watching a violinist, for example, we experience the sight and sound together rather than feeling that they are part of two separate perspectives.
The origin of this core consciousness occurs when we start to be aware of any events inside and outside our bodies – such as the pain of colic or the calming sound of a parent’s voice – and are able to distinguish between them.
For most of us, the point at which this happens may seem obvious. Babies cry when they are hungry and sleep when they are content. But in the not-so-distant past, the medical profession treated infants as if they had no inner world. Until the 1980s, for instance, surgeons would operate on babies without any analgesic or anaesthetic. The assumption was that painkillers weren’t necessary, since babies couldn’t truly feel discomfort. The protocol has now changed – but the question of when conscious awareness appears remains unresolved.
This is largely because we can’t really know about a baby’s inner life until they can talk and tell us what they are thinking or feeling. We can try to draw , such as the fact that newborn babies are more likely to turn their heads towards their mother’s voice, compared with a stranger’s. To some, this is evidence that consciousness has an early onset – but others remain sceptical that this reflects anything more than an automatic reaction, without any awareness.
Bayne and his colleagues suggest a practical approach to settle the debate. They point to recent research identifying four patterns of brain activity and behaviour associated with conscious awareness in adults. While none of these consciousness markers can, by itself, guarantee the presence of an inner life, taken together, they give a strong indication that someone is aware of their surroundings. And if we can identify the same markers in babies, then we might assume that they also possess core consciousness.
“We may, in the fullness of time, develop a kind of crucial test that can act like a thermometer for consciousness,” says Bayne. “But we’re a million miles away from that right now, and so I think the best way to go is to look for lots of different tests, and if they all point in roughly the same direction, then you know you’re onto something.”
The four tests of awareness
The first consciousness marker that Bayne and his colleagues considered concerns the ways that different brain regions temporarily link up into working networks. Brain scans reveal that, when we are at rest and daydreaming, the default mode network (DMN) takes over. If something captures our attention, the executive control network (ECN), which is a set of brain areas responsible for goal-oriented thinking, comes online in combination with the dorsal attention network (DAN). People who are asleep and dreaming, which is considered by most to be a conscious state, show this ebb and flow of activity between the DMN and the ECN and DAN, but those under anaesthesia don’t – leading Bayne and his colleagues to select it as a marker of consciousness.
Measuring brain activity in babies is no mean feat. In the past, fMRI scanners required the subject to sit very still, but babies have an annoying habit of wriggling. “Movement degrades the image quality,” says at Trinity College Dublin, Ireland. Improved algorithms, however, allow scientists to correct for the baby’s motion, resulting in a much better view of their brain activity.
In 2022, Naci and her colleagues of more than 280 full-term newborns as they slept in an fMRI scanner, finding that the hallmarks of the DMN, DAN and ECN – and the reciprocal activity between them – were already in place. Interestingly, this was also true of preterm babies once they had reached the equivalent age, but not before. “There was a lower limit,” says Naci. This suggests that, in a typically developing fetus, the networks may develop in the very last stage of pregnancy.
The mere presence of these networks doesn’t reveal much about the contents of a baby’s awareness or the way they are perceiving the world. This comes from the team’s second marker, which concerns the neural activity associated with a shift in attention. A core element of conscious awareness is the ability to move our focus from object to object in our surroundings. Measuring this is simple – just observe the changes in participants’ gaze as they look at different stimuli. In adults, the shift tends to correspond to heightened activity in the frontal cortex, a brain region responsible for many higher-level cognitive functions. Crucially, in 2021, researchers found very in 3 to 12-month-olds.
The McGurk effect
Bayne and his colleagues’ third marker is “multisensory integration”. Our brains often combine incoming information from different organs, meaning that signals from one sense can influence the conscious perception of signals from another. In experiments with adults, for instance, participants were asked to watch a video of someone saying one sound (such as “ba-ba”) but listen to the audio of them saying another (such as “ga-ga”). Most people perceive “da-da” as a mental compromise between the conflicting stimuli – a phenomenon known as the .
It is trickier to do this test on babies as they can’t tell us if they are perceiving “ba”, “ga” or “da”. But they often show a preference for sounds that feel familiar and remain focused on the source of such sounds for longer. So, if an infant experiences the McGurk effect, this should increase the familiarity of the “da” sound – enhancing their attention when it is played. In 2004, at Western Sydney Univesity and at the University of Queensland, both in Australia, used this method to show that babies . This strongly suggests that their brains are integrating the information from the different senses into a single, unified experience.
There is a question mark over whether fetuses are conscious in late pregnancy
Bayne and his team’s final marker of consciousness comes from an experiment using the oddball paradigm, which tests the mind’s ability to keep track of patterns. It involves playing a series of tones, with intermittent variation over both short and longer periods. If you imagine it as a simple musical score, you might have a series of bars with three Cs, for example, followed by a D. That bar is then repeated multiple times until, one time, you have a new bar of four Cs – the oddball.
Research in 2009 found that awake travelling across the cortex around 300 milliseconds after the short and long-term patterns have been violated with the oddball. This so-called P300 response to both pattern violations suggests the brain is keeping track of these sound sequences, and only appears to occur when people are conscious of what they are hearing.
To find out if young babies show the same neural reaction, at the University of Tübingen in Germany and her colleagues placed 20 newborns in a cradle of magnetic sensors that were able to measure small fluctuations in their brain activity as they listened to the sequence tones. Quite remarkably, they showed a neural response that was very similar to the P300, although the time lag between the oddball and the brainwave was longer than in conscious adults.
In a , Bayne and his colleagues argue that, taken together, these four lines of evidence would certainly seem to suggest that very young babies have conscious awareness. “The critical networks involved in consciousness were present and seem to be active much earlier than anyone had thought,” says Bayne.
If consciousness is present at birth, it is reasonable to speculate whether it might also be present during the last few weeks of gestation. There is limited evidence supporting that idea. Using very sensitive magnetic sensors, it is possible to detect brain activity in the uterus. One study suggests that 35-week-old fetuses do – although there are enough differences from the patterns seen in conscious adults that this conclusion remains controversial. Either way, the research has few implications for the debate on abortion, as interventions so late in pregnancy are rare.
Passos-Ferreira is open to the possibility that consciousness arises before birth, though she suggests the fetus might be . These may inhibit neural activity without necessarily eliminating conscious awareness of external stimulation entirely. “My best bet is that they are , but there is a question mark over whether they have the capacity for consciousness in late pregnancy,” she says.
Emergence of experience
The debate is far from settled, however. In a to Bayne and his colleagues’ paper, philosopher and psychologist , both at the University of Birmingham, UK, question whether it is fair to focus solely on the indicators of basic perceptual awareness without considering more sophisticated mental abilities. These might include intentionality, which is the capacity to complete an action in order to meet a goal, and explicit memory – the ability to recall an event and then replay it at a later point.
“If you think that consciousness is linked to some high-level cognitive abilities, which quite a lot of people believe, then you can make the case that newborn infants are unconscious,” says Taylor. Unsurprisingly, your view on when consciousness emerges depends on how you define consciousness in the first place.
To try to find a more objective set of consciousness markers, Taylor and Bremner suggest looking more closely for correlations between the different markers. It could be that certain markers are present or absent independently of the others, which would suggest that they are less reliable as an indicator of consciousness, so can be discounted.
Alternatively, we may find that two markers always appear together, or that the emergence of one strongly predicts the development of others at an older age. This might reveal consciousness to be a gradual process, with the building blocks slotting together as the child’s brain develops. “I’m pretty convinced that when you disambiguate all those different kinds of consciousness, you’re going to find them coming online at different times,” says Taylor.
Such investigations may help refine our definitions and theories of consciousness more generally. Integrated information theory (IIT), for instance, argues that subjective experiences emerge from the way data is processed and combined in the brain, so that the integrated total is more than the sum of its parts. Although the idea remains controversial, some researchers argue it is possible to that is being integrated from measures of neural activity – including those of young babies. Comparing this with the other markers of emerging consciousness and seeing how they change as a baby ages, could offer evidence for IIT – or indeed for , which abound.
Such advances may allow us to better understand what a baby’s experience feels like. The research so far suggests that, if they have conscious experience, it may be very different from our own. Whereas adults have a very fine focus of attention, that of babies may be much more diffuse. In the words of the developmental psychologist Alison Gopnik at the University of California, Berkeley, it may be , with a conscious experience that comprises a huge amount of sensory detail distributed more evenly across their environment. Or in other words, suggests Bayne, “perhaps everything’s conscious all at once”.
