IMAGINE being able to watch your baby's mind starting to work. That has now been achieved by looking at electrical activity in the very young brain. Insights from the study may help us monitor babies under anaesthesia and improve our understanding of consciousness in adults – and perhaps in animals, too.
The human brain develops dramatically in the first year of life, transforming a baby from being unaware to fully engaged with its surroundings. To capture this change, Sid Kouider at the École Normale Supérieure in Paris, France, and colleagues used electroencephalography (EEG) to record electrical signals in the brains of 80 very young children.
In adults, becoming aware of a stimulus is linked to a two-stage pattern of brain activity. After a visual stimulus, for example, areas of the visual cortex fire, followed about 300 milliseconds later by areas such as the prefrontal cortex, which deals with higher-level cognition. Studies show that conscious awareness – the moment when adults can verbally confirm a stimulus – kicks in only when this second stage of neural activity reaches a specific threshold.
To investigate whether small children respond in the same way, Kouider's team put EEG caps on babies aged 5, 12 and 15 months, recording brain activity as they were shown rapidly changing images. Most of these were of random ovals, but among them was a face.
Each group responded to the face with the two-stage pattern of brain activity. But the second stage took much longer to reach in 5-month-old babies than in the older groups. In 12 and 15-month-old babies the second stage arrived 800 to 900 milliseconds after the face was displayed. In the youngest infants, there was a delay of about 1200 milliseconds (Science, doi.org/k95). "Babies have the same mechanisms as adults, but they are very slow," says Kouider.
The activity is consistent with anatomical studies which show that the neurons in babies' brains are not yet fully covered with a fatty insulating sheath. This physiological immaturity could explain the delayed signals, says Kouider.
"The results give a really good handle on visual awareness in infancy," says Natasha Sigala at the Brighton and Sussex Medical School, UK. It may also explain why we are unable to form memories at a very young age. "My personal view would be we cannot have memory without perception in place."
Ron Chrisley at the Sackler Centre for Consciousness Science at the University of Sussex in Falmer, UK, suggests that if animals show similar two-stage patterns of brain activity, then we would have good grounds for attributing consciousness to non-humans. But "there might be more than one way in this universe to be conscious", he says.
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