The Development of Consciousness in Infants

Post by Laura Maile

What is consciousness?

Scientists have long attempted to understand where consciousness resides, whether it involves a network of brain areas, and when in development it emerges. Current theories of human consciousness state that consciousness develops as the brain becomes capable of integrating information, making us aware of ourselves and our environment. There are many different theories, however, on how and where consciousness is represented. Higher-order theories, for example, require that one be able to represent an external experience in the mind, and place importance on the prefrontal cortex. In contrast, integrated information theory places more emphasis on posterior cortical areas, and rests on the ability of the brain to integrate different stimuli to generate information by the whole. In general, it is agreed that consciousness is represented in the brain, likely as an integration of signals across multiple brain areas.  

How do you measure consciousness?

It is of critical importance to develop and agree upon measures of consciousness, specifically for infants, as they are unable to follow directions or communicate verbally. Infants do possess the ability to respond to stimuli such as the sound of their mother’s voice, different facial expressions, and noxious stimuli. Their responses can be measured both behaviorally, through limb withdrawal, facial grimacing, eye movement, vocal and sucking activity, and physiologically, with changes in heart rate and neural activity in brain areas that respond to environmental stimuli. Most current theories of consciousness are based on physical processes that can be measured via electroencephalogram (EEG) recordings and fMRI, and behavioral indicators of consciousness, such as the capacity to respond to environmental stimuli. fMRI studies, which record high-resolution hemodynamic activity in the brain that respresents neural activity, have identified cortical “hubs” and networks of brain regions that are active during different activities and states. By studying brain activity across different states of development, scientists have determined how functional networks change over time. Conceptually similar to EEG, which uses a net of electrodes fitted to the skull to record brain activity, magnetoencephalography (MEG) is a less invasive alternative that can be used to measure fetal brain activity. 

When does consciousness emerge?

There are conflicting theories about when exactly consciousness appears during development. Some theories, for example, require that individuals have a sense of self and an understanding of their own mental state in order to be qualified as “conscious,” which would mean that humans are not conscious until some time after their first birthday. Other recent evidence indicates that consciousness may appear in early infancy or even before birth, as soon as thalamocortical activity appears in the brain at about 24-26 weeks gestation. Rather than base our understanding of the emergence of consciousness on a specific theory or set of conflicting theories, some scientists suggest that the field measure markers of consciousness in adults and observe when they first emerge in infants. 

Activity in the brain shows that the primary cortical areas that process vision, auditory, and sensorimotor information are active in response to external stimuli at birth, indicating that newborn babies can process many sensory inputs. Some of these areas are also present and active prior to birth in the developing fetus. Those brain areas involved in more complex processes such as attention, executive function, and memory appear less complex at birth and develop over the first two years of life. Some specific functional activity networks have been linked to the capacity for or recovery of consciousness after injury in adults. Three of these networks, the default mode network, dorsal activity network, and executive control network, have recently been identified as distinct and functional networks in newborn babies.  

Behavioral data shows that shortly after birth, infants can process auditory and visual inputs that allow them to recognize their mother’s voice, show sensitivity to music, and even show preference for their native language. Visual acuity is low at birth, but brain imaging data shows responses in the visual pathway to distinct visual inputs at two months of age. While most perceived senses expand and develop as the infant ages, there is also data indicating that young infants aged 4-6 months can perceive more distinct sounds and faces than older infants and adults. Additionally, multisensory integration that requires conscious perception of individual stimuli has been demonstrated in 4-5 month old infants. 

What's next?

The study of infant consciousness has become an increasingly important and studied topic in the field of consciousness research. Continued improvement in methods to measure brain activity and other markers of consciousness in fetuses and infants is needed. A more complete understanding of the neural correlates and functional basis of consciousness will also require a tightening of the many theories of consciousness into one universally accepted theory. 

The takeaway

A definitive answer on when human consciousness begins has yet to be identified, but the increase in studies on conscious experience in infants and preterm fetuses is bringing us closer to one. Recent evidence points to an earlier onset of consciousness than was previously described in human infants, indicating some level of consciousness is present at birth, and potentially even in the late stages of gestation when brain activity and behavioral responses to external stimuli can be measured. 

References +

Bayne, T et al., Consciousness in the cradle: on the emergence of infant experience. Trends in Cognitive Sciences. 2023.

Padilla, N et al., Making of the mind. Acta Paediatrica. 2020.

Seth, AK et al., Theories of consciousness. Nature Reviews Neuroscience. 2022.