Login
New research is beginning to shed light on one of the most enduring mysteries of the human mind — when does consciousness first emerge in infants?
A new review paper argues that converging evidence points to consciousness likely being present earlier than previously thought, possibly even before birth.
The review, published in Trends in Cognitive Sciences, examined brain waves, behaviors and senses that mark the start of awareness in adults, showing that some key signs are active in newborns or appear within months after birth.
Brain responses to surprises — which signal awareness in adults — were detectable in fetuses as early as 24-26 weeks.
The authors said that taken together, the findings suggest consciousness could be present in late pregnancy, but that more work is still needed to unravel the origins of experience.
Led by Tim Bayne, Ph.D., at Monash University, Melbourne, Australia, the international team of neuroscientists and philosophers reviewed infant brain imaging studies that claim to detect consciousness and distinguish it from its absence.
Their research revealed that babies have a more immature visual sense than auditory sense, are conscious of fewer items than adults and take longer to comprehend visual cues. But infants can process diverse information, like sounds from different languages, better than older individuals.
Bayne and co-authors presented the following four lines of evidence supporting the early emergence of consciousness in infants:
1. Brain connection networks
A hallmark of consciousness is the ability to process and prioritize stimuli as they occur and to plan accordingly.
One component of this ability is the default mode network (DMN), a system of brain areas associated with mind-wandering and consciousness, which is present soon after birth.
The DMN is active when things are going on around a person but they daydream instead of mentally engaging with their surroundings.
Past research showed marginal DMN activity in infants, but a more recent examination of brain scan data showed that much more is going on.
A 2022 study found that DMN exists with two other consciousness mechanisms: DAN (dorsal attention network) and ECN (executive control network). DAN is the brain’s “prioritizer” which allocates attention or importance to events and things around us, while ECN helps us to plan, monitor and execute goals.
Bayne wrote that the existence of these networks indicates that “neural circuitry associated with consciousness might be in place at birth.”
2. Attention mechanisms
Although attention and consciousness are not the same, the latter would not exist without the former.
Children develop top-down or voluntary attention — the ability to follow things or events of interest — at between 3-6 months. But the bottom-up involuntary variety — for example, in response to a startle or physical contact — is evident from babies’ eye movements at birth.
If consciousness requires bottom-up attention, then consciousness could emerge as early as birth, Bayne argues.
3. Combining sensory cues
Also known as “multisensory integration,” combining sensory cues involves understanding the connection between two or more stimuli of different types — for example, spoken words (sounds) and lip movements (sights).
While multisensory integration occurring unconsciously is limited, an advanced form of this type of mental processing occurs in very young children. This suggests that consciousness develops no later than about 4-5 months.
4. The local-global paradigm
“Local-global” refers to the perception of complex objects or events, specifically whether an individual sees details or the big picture first.
The ability to switch from the local (details) to the global (big picture) as the situation demands is a sign of consciousness.
An early study discovered this ability at 3 months, while more recent papers report it at birth and in fetuses older than 35 weeks.
The authors noted that while signs of consciousness appear earlier than previously believed, such factors as premature birth could affect the timing of this developmental milestone.
Evidence for early emergence of bodily self-awareness
The evidence for developing consciousness in early infancy is based on externally observable or measurable signs, biomarkers and behaviors.
However, consciousness may develop much earlier than birth, even earlier than 35 weeks gestational age, through an unborn child’s awareness of and reactions to events inside his body.
Bayne uses the analogy of adults floating in sensory deprivation tanks that simulate a womb. While inside, adults experience a heightened awareness of self despite, or perhaps because of, the absence of external stimuli.
The evolution of consciousness is mostly about expanding perception — recognizing and responding appropriately to a wider variety of experiences. But “perceptual narrowing,” whereby infants lose certain discriminative abilities, also occurs.
For example at 6-10 months, most infants in English-speaking homes can differentiate Hindi consonants. But they lose that ability by 10 months.
Perceptual narrowing also occurs in facial recognition, where 3-month-olds recognize people of other races but lose much of that ability by 9 months.
Emerging methods for assessing consciousness
How and when consciousness begins remains a mystery, but methods developed to study consciousness in non-human animals and brain-injured individuals are providing clues.
Advances will depend on new ways to utilize existing brain imaging techniques and analyze their data.
Recent developments in magnetoencephalography (MEG) — an imaging method that studies brain activity through the magnetic fields arising from the brain’s electrical activity — is one method.
Functional magnetic resonance imaging (fMRI) — an offshoot of MRI imaging used to detect cancer and other abnormalities inside the body — is another.
Both methods show which areas of the brain are involved in responses to stimuli. They are used both to diagnose irregularities and to establish normally operating brain connections.
But both have shortcomings: MEG only crudely identifies which areas of the brain are involved in a response, while fMRI cannot pinpoint precisely when a response occurs.
A third imaging-based technique for measuring brain activity, perturbational complexity index (PCI), originally developed to detect consciousness in unresponsive individuals, might resolve the temporal and spatial limitations of MEG and fMRI.
PCI involves magnetically stimulating the brain and calculating the complexity of the response over time and across brain regions.
PCI claims it can give a yes/no answer as to whether consciousness exists. It differs from conventional imaging, which measures ongoing brain activity, in its ability to quantify the brain’s capacity to sustain complex internal interactions.
But there is the rub: Because its full effects on developing brains are unknown, magnetic brain stimulation in infants is unethical unless it is medically necessary.
However, in a June 2023 study, Bayne and co-authors proposed a “sensory” version of PCI that uses safer, more familiar stimuli — sights, sounds, or smells — rather than magnetic stimulation.
Unanswered questions
Bayne concluded his review with a list of unresolved questions:
- Does the transition from unconsciousness to consciousness occur suddenly, or does consciousness emerge piecemeal? Might different aspects of consciousness, like the realization of events inside and outside the body, become evident at different times?
- Do states between consciousness and unconsciousness exist?
- Can we generalize from adults to infants given the developmental and functional differences between adults and infants or fetuses?
- Do infants or fetuses dream and, if so, of what?
