Finding the point at which babies’ reactions change from being purely reflexive to reflecting more intention is leading researches to focus on the first glimmers of conscious thought in infants as young as 5 months old.
“We can prove that the same neuromarkers of consciousness found in adults can be found in babies as early as five months of age,” says lead author Sid Kouider, a researcher at the École Normale Supérieure in Paris, of his new study on the earliest signs of conscious thought in infants that was published in Science.
To look for consciousness in babies too young to talk, the authors took advantage of research on visual perception, which showed that the brain processes a great deal of visual information before any of it reaches a level of conscious awareness. EEG signals, which are measured by placing electrodes on the head, can clearly distinguish between visual data that is consciously seen and that which is simply taken in by the brain. These signals show a major change when a person first becomes consciously aware of an object that has previously received only subliminal attention.
“There are two stages of perceptual processing,” explains Kouider. “The first stage is basically activation of neurons in the sensory cortex. Just a little visual stimulation — even if you can’t see it consciously — is going to activate [this brain region].” The brain still shows electrical activity on an EEG, for example, even if images or words flash by so quickly that they aren’t consciously perceived. (This information registers somewhere in the brain, however, because such “subliminal” data can affect responses to later tasks).
The second stage, which can be reported verbally by adults, comes with a different signal and is essentially either “all” — when you can see it — or “none,” if the object isn’t visible at all, indicating a conscious level of attention and processing.
To better understand how, and when these different levels of perception might be engaged in babies, the researchers placed EEG caps on 30 5-month-olds, 29 1-year-olds and 21 15-month-old toddlers and had them look at images of faces to determine whether they would generate the signals associated with the second, more intentional type of processing. And indeed, Kouider says they found that the babies’ brains traced the same signature of consciousness as adult brains.
“What changes basically is that the neural signal of consciousness we observe is weaker at five months,” he says, “It’s less stable and it’s much slower.” Indeed, a 5-month-old must see an image for four times longer than adult would to show a signal of conscious visual awareness — and this takes three times longer for 12- and 15-month-olds.
“It’s intriguing,” says Lise Eliot, associate professor of neuroscience at the Rosalind Franklin University of Medicine and Science in Chicago and author of What’s Going On in There?, which examines infant-brain development. Eliot notes that while previous research suggested that there might be signals of consciousness in infants, “This is a much more elegant, carefully controlled study and they do have a lot of the adult parallels to relate this to.”
Kouider and his colleagues plan to look at even younger babies next, as they try to determine at what age the signal first appears. The results could have implications for expanding our understanding what consciousness is and how it develops in the brain. “It would be neat if you could use infants to figure out what consciousness is because it suddenly appears at some age,” says Eliot.
Kouider says he’s not surprised that consciousness is not as well developed in infants as it is in adults because it requires interplay between the prefrontal cortex (PFC) and sensory brain regions — and during the first three years of life, the connections between those regions aren’t very robust since the PFC and the wiring of those connections are still developing. “If [a perception is] not going to be subliminal, it has to involve the PFC,” he says, “We know from anatomical studies that the PFC is underdeveloped until the second year of life. It’s not nonexistent, it’s just not fully functional.”
The research also has more practical implications. Ideally, the infant studies would enable scientists to trace a trajectory of how consciousness generates. “You can start to use this method very early to basically try to check whether there is normal or abnormal development,” Kouider says. “We know that autistic children can have trouble being aware of faces, and you could imagine this kind of method to diagnose early on whether someone is reacting in a normal way to objects or faces.”
So while the youngest babies may not be conscious of much, they can provide valuable information about how conscious thought emerges, and how it develops over time. And with that understanding, we may learn a great deal about what it means to be aware.