sciencemag | For everyone who's looked into an infant's sparkling eyes and
wondered what goes on in its little fuzzy head, there's now an answer.
New research shows
that babies display glimmers of consciousness and memory as early as
5 months old.
For decades, neuroscientists have been searching for an unmistakable
signal of consciousness in electrical brain activity. Such a sign could
determine
whether minimally conscious or anesthetized adults are aware—and
when consciousness begins in babies.
Studies on adults show a particular pattern of brain activity: When
your senses detect something, such as a moving object, the vision center
of your brain
activates, even if the object goes by too fast for you to notice.
But if the object remains in your visual field for long enough, the
signal travels from
the back of the brain to the prefrontal cortex, which holds the
image in your mind long enough for you to notice. Scientists see a spike
in brain activity
when the senses pick something up, and another signal, the "late
slow wave," when the prefrontal cortex gets the message. The whole
process takes less than
one-third of a second.
Researchers in France wondered if such a two-step pattern might be
present in infants. The team monitored infants' brain activity through
caps fitted with
electrodes. More than 240 babies participated, but two-thirds were
too squirmy for the movement-sensitive caps. The remaining 80 (ages 5
months, 12 months,
or 15 months) 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, in Paris watched for swings in electrical activity,
called event-related
potentials (ERPs), in the babies' brains. In babies who were at
least 1 year old, Kouider saw an ERP pattern similar to an adult's, but
it was about three
times slower. The team was surprised to see that the 5-month-olds
also showed a late slow wave, although it was 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 2 months.
This late slow wave may indicate conscious thought, Kouider and colleagues report online today in Science. The wave, feedback from the prefrontal cortex, suggests that the image is stored briefly
in the baby's temporary "working memory." And consciousness, Kouider says, is composed of working memory.
