A mother holds a 5-month old baby wearing an electrode cap to measure the child's conscious experiences.
Credit: Sid Kouider
Infants have a conscious experience of the world at as early as 5 months of age, new research finds.
New parents may raise an eyebrow at the idea that their baby might not be a conscious being, but scientists have, until now, not been able to clearly show that infants react with awareness rather than reflexively. Even in adults, much of the brain's processing of the world occurs without conscious awareness, said Sid Kouider, a neuroscientist at the Laboratoire de Sciences Cognitives et Psycholinguistique in Paris and the Technical University of Denmark.
One odd phenomenon, "blindsight," occurs in people with damage to part of their visual cortex. Although they cannot consciously see, they're able to "guess" the location of a visual stimulus or even catch objects tossed at them. Blindsight reveals that even unconscious processing in the brain can result in seemingly goal-directed behavior. [9 Bizarre Medical Conditions]
So when babies look toward a face or grasp an object, they, too, might be doing so without a conscious experience of what they're seeing.
"Infants might be responding in a kind of automatic manner," Kouider told LiveScience. Unfortunately, since babies don't talk, scientists can't test consciousness by asking infants what they experience.
Baby brain patterns
So Kouider and his colleagues turned to brain activity for a peak into babies' awareness. When adults are shown a subliminal image, their brains show a spike in electrical activity in sensory regions — even though they may not consciously register that they've seen such a brief image.
When the image does consciously register, however, the brain shows a second leap in activity, typically about 300 milliseconds after the presentation of the image. This pattern reveals visual consciousness, Kouider said, which means that not only does the brain respond to the image, but also the owner of that brain perceives that response and has a conscious experience of the image.
The researchers wanted to know whether babies would show this same brain pattern. They recruited 30 5-month-olds, 29 12-month-olds and 21 15-month-olds and fitted the babies with electrode caps that measure the brain's electrical activity through the scalp.
Next, the babies sat on their mother or father's lap while watching a screen with a patterned image. For a fraction of a second (ranging from as quick as 17 milliseconds up to 300 milliseconds), the researchers flashed a photo of a face on the screen.
The scientists then analyzed the babies' brain activity to search for the two-phase pattern that would indicate consciousness. They found it: Babies did indeed show a secondary spike in neural activity, just like adults.
But there was one important difference between the babies' neural patterns and those seen in adults, Kouider said. In 5-month-olds, it took 1.3 seconds for the second flurry of brain activity to show up. In adults, the timing is closer to three-tenths of a second, or 0.3 seconds.
"It's about four times slower, actually, in the younger infants," Kouider said. [11 Things Parents Should Know About Their Babies' Brains]
Older babies show snappier processing, though still not as quick as adults, the researchers found. In 12- to 15-month-olds, the second phase is stronger than in 5-month-olds and occurs around eight-tenths to nine-tenths of a second.
The reason for this delay probably has to do with the undeveloped nature of a baby's brain, Kouider said. The second phase of activity that accompanies consciousness arises because the visual parts of the brain send information to the prefrontal cortex, which sits in the front of the skull. The prefrontal cortex directs and maintains attention and is crucial to consciousness. This part of the brain also develops slowest, going through major changes at about a year of age.
Babies' brains also lack myelin, a fatty substance that sheathes nerve fibers in the brain. Myelin acts as insulation, speeding up signals from one area of the brain to another. Before the brain is fully myelinated, neural impulses don't move as quickly from the visual brain regions at the back of the brain to the prefrontal cortex as the front.
Conscious of pain?
The findings will be published Friday (April 19) in the journal Science. While parents can rest assured that their babies have a conscious experience of mom, dad and probably Elmo, the results have broader implications for medicine.
For example, Kouider said, researchers may be able to use similar brain-monitoring methods to determine when babies develop a conscious experience of pain. Until the 1980s, pain-relieving anesthesia was not automatically given to infants undergoing surgery, because doctors believed that infant pain was merely a reflex, not a conscious experience. (Surgeons weren't trying to be heartless: Anesthesia brought extra risk of death to the infant, a risk doctors didn't want to take given the accepted notion that babies weren't bothered by pain anyway.)
"Our study suggests that babies are much more conscious than we believed before, and they're probably much more conscious of pain when they experience [it]," Kouider said. Researchers might also be able to detect abnormalities in conscious experience before babies learn to talk, he added, perhaps leading to earlier diagnoses of disorders such as autism.
The researchers now plan to use even more inviting stimuli, such as toys babies like, to test whether familiar objects garner a quicker brain response. They also plan to test babies as young as 2 months old for consciousness.