This 5-month-old boy helped scientists figure out when consciousness… (Image courtesy of Sid Kouider/Science )
Babies wise up fast. By the time infants are 3 months old, their unfinished brains are laced with a trillion connections, and the collective weight of all those firing neurons triples in a year.
But the indecipherable babbling and maladroit wiggling so beloved by parents just leave scientists in baby labs scratching their heads. What do those little people know, and when do they know it?
A team of French neuroscientists who compared brain waves of adults and babies has come up with a tentative answer: At 5 months, infants appear to have the internal architecture in place to perceive objects in adult-like ways, even though they can't tell us.
"I think we have a pretty nice answer," said Sid Kouider of the Ecole Normale Superieure in Paris, whose findings were published Friday in the journal Science. "Babies as early as 5 months, and probably earlier, are displaying the same neural aspects of consciousness as adults."
The findings hint at an early shift from a largely passive biological process shared with other animals to the uniquely human ability to ponder ourselves and our surroundings in complex and abstract ways.
Researchers spent the better part of five years fiddling with fussy babies — at 5, 10 and 15 months of age — who had to sit still while wearing a cap with 128 electrodes and watching images flicker before them at eye-blink intervals.
"This was heroic," said UCLA developmental psychologist Scott Johnson, who was not involved in the study. "It must have taken them forever."
Said Kouider: "We had to be very patient."
Researchers have spent decades observing infants' eye movements, attempting to delve into such issues as memory, cognition and perception. But there is a limit to what they can infer.
"Four-month-olds can predict trajectories of objects, but do they have a conscious projection of a ball? Does she wonder, 'Where is that thing?'" Johnson said. "It's a question we wrestle with."
Kouider relied on studies of adult brain waves recorded while subjects were presented with images that flashed for milliseconds. Some images were recognizable, such as a numeral, while the rest were indecipherable. The study volunteers were asked if they had "seen" anything.
In adults, the brain processes fleeting images — presented for less than 200 milliseconds — in a way that prevents us from consciously perceiving them. That finding that has broadened scientists' understanding of subliminal suggestion and priming of human behavior.
But when images flash for at least 300 milliseconds — roughly the duration of an eye blink — brain activity increases exponentially, like a seismometer needle responding to a tremor. That's also when adults can report that they consciously perceived the image.
The French team recorded equivalent brain waves in the 80 infants who could sit still while wearing their electrode caps. While the adult-like wave forms were somewhat weaker and delayed in 5-month-olds, they were strong and sustained in the older babies, the researchers reported.
Charles Nelson, director of developmental medicine at Boston Children's Hospital, cautioned that the French scientists may be over-interpreting data.
"The study is well done," said Nelson, who wasn't involved in the Science study but has done similar research. "They just take the inference too far."
Brain wave data and brain activity measured by functional MRI scans alone cannot imply a behavioral state, Nelson warned.
"If that were true, I should be able to look at your [electroencephalogram and MRI] response and know what you're thinking or feeling, and we know that is not the case," he said.
Kouider acknowledged that the study describes brain function, not the content of the babies' thoughts.
Further research may unveil what babies actually know but just won't tell us, he said.