Neuroscientists have been searching for signs of consciousness in electrical brain activity for decades. These signs could determine whether minimally conscious or anesthetized adults are aware, and when consciousness begins in babies.
When an adult's senses detect something like a moving object, the vision center of the brain activates, even if the object is moving too fast to notice. When the object remains in the visual field for long enough, the signal travels from the back of the brain to the prefrontal cortex, which holds the image in the mind for long enough to notice.
There is a spike in brain activity when the senses first notice something, and another signal, the "late slow wave" when the prefrontal cortex receives the message. The entire process takes less than one-third of a second.
A team of scientists in France conducted research to determine if the two-step process occurs in infants. The infants' brain activity was monitored through caps fitted with electrodes. More than 240 babies participated but two-thirds moved too much for the movement-sensitive caps. The remaining 80 were shown a picture of a face on a screen for a fraction of a second.
Cognitive neuroscientist Sid Kouider of CNRS, the French national research agency, watched for changes in electrical activity, called event-related potentials (ERPs). The research found ERP patterns similar to adults in babies as young as five months, although the signals are weaker and more drawn out than in the older babies. Kouider speculates that the late slow wave may be present in babies as young as two months.
The late slow wave may indicate conscious thought, because it suggests that the image is stored briefly in the baby's temporary "working memory." And consciousness is composed of working memory, according to Kouider.
Although the team showed remarkable patience in gathering data from infants, says cognitive neuroscientist Lawrence Ward of the University of British Colombia, the work may not be conclusive. "I expect we'll find several different neural activity patterns to be correlated with consciousness," says Ward, who was not involved in the study.
Comparing infant brain waves to adult patterns is difficult, says Charles Nelson, a neuropsychologist at Harvard Medical School in Boston. "ERP components change dramatically over the first few years of life. I would be reluctant to attribute the same mental operation (i.e., consciousness) in infants as in adults simply because of similar patterns of brain activity."
"He's right, the ERP components are not exactly the same as in adults," says Kouider, but the ERP signature he saw had the same characteristics.
Kouider hopes to explore how these signs of consciousness relate to learning, especially language development. "We make the assumption that babies are learning very quickly and that they're fully unconscious of what they learn," he says. "Maybe that's not true."
