Disputed signs of consciousness seen in babies’ brains

Infants display neural responses linked to visual awareness by 5 months of age

Babies’ brains emit electrical bursts that signal a budding awareness of the visual world by the time they are 5 months old, a new study concludes. But some researchers are skeptical that these neural surges correspond to conscious experience.

THE BABY ELECTRIC Infants, including this 5-month-old boy fitted with an electrode-covered cap and held by his mother, display electrical brain responses possibly representing visual awareness, a new study finds. S. Kouider

From age 5 months to 15 months, the brain begins to develop the ability to register and remember sights, according to the research by cognitive neuroscientist Sid Kouider of École Normale Supérieure in Paris and his colleagues. The researchers showed babies images that included faces flashed increasingly slowly on a screen. They started at a speed so fast that even adults wouldn’t consciously notice the images, and then the researchers increased the amount of time each image appeared. Infants displayed a sequence of rapid brain responses that first signaled unconscious and then conscious perception of faces, Kouider’s team reports April 18 in Science.

“We weren’t expecting to see any evidence of a neural marker for consciousness in 5-month-olds,” Kouider says. Babies at that age exhibited a weak, delayed version of a brain response that occurs when adults report seeing a face flashed just long enough to be consciously perceived, Kouider asserts.

Stronger and faster brain responses corresponding to visual awareness emerged in 12- and 15-month-olds, Kouider found, although older infants still fell well short of the adult pattern.

If further research confirms the existence of a neural marker of consciousness in babies, scientists could adapt their visual task to evaluate whether infants show brain indications of feeling pain during medical procedures or after receiving numbing drugs, he suggests.

But cognitive neuroscientist Charles Nelson of Harvard Medical School sees no clear connection between the findings in infants and the electrical responses in adults’ brains. “I would be reluctant to attribute the same mental operation, such as consciousness, to infants and adults simply because of similar patterns of brain activity,” Nelson cautions.

Electrical responses in the brain linked to sensations, thoughts and behaviors change dramatically over the first few years of life, Nelson says. The brain responses proposed by Kouider’s group as underlying infant consciousness don’t clearly correspond to those linked to visual awareness in adults, Nelson holds.

In the new study, 5-month-olds, 12-month-olds and 15-month-olds sat on their mothers’ laps while wearing an electrode-studded cap that measured electrical activity on the brain’s surface. The babies saw three scrambled images and a woman’s face, flashed on a computer screen for various amounts of time, accompanied by bell sounds for each image that created a simple melody to attract the infants’ attention.

In the same setup, adults don’t report seeing a face and don’t display a neural marker of consciousness until each image appears for nearly one-third of a second. For 12- and 15-month-olds, each image had to be presented for about three-quarters of a second — and for almost one second for 5-month-olds — for the children to indicate conscious perception by looking toward the faces and generating the proposed brain signature of visual awareness.

No one has yet confirmed that a string of electrical responses in the brains of either adults or children reflects a transition from unconscious to conscious perception, remarks cognitive neuroscientist Teodora Gliga of the University of London’s Birkbeck College. But Kouider’s team has designed a way to investigate conditions under which infants, and possibly nonhuman animals, respond to and learn from their environments, an important achievement in itself, Gliga holds.

That’s not to say that babies can’t be aware of their surroundings, as some researchers have argued. “Five-month-olds and even younger infants probably have many real-life opportunities to consciously process information,” Gliga says.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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