Carlos Solis
If you can read this, you’re probably sure of one thing: you’re conscious. Your relatives, neighbors, and friends seem conscious too — they act like people and appear to share a similar experience of the world. But what about tiny infants who don’t understand their surroundings and can’t tell us about them? We don’t remember what it’s like to be that small. Do they have consciousness? And what about those who haven’t been born yet?
Those questions have drawn growing attention from neuroscientists in recent years. “There’s surprisingly little research on when consciousness begins,” says neuroscientist Joel Frohlich. For a long time, consciousness was mainly a philosophical question; neuroscientists barely studied it until the last 10 to 20 years.
Not a single marker — a cluster of clues
Frohlich and philosopher Tim Bayne propose a tentative answer: around five months of age. At about that age, infants show a set of signs that suggest they have genuine experiences of the world.
They use what they call a “cluster” approach: instead of hunting for one universal marker of consciousness, researchers collect a range of clues — patterns of brain activity, reactions to stimuli, and signs of attentive, aware behavior. “One marker alone isn’t enough to trust completely,” Frohlich says. “But when several small markers line up, that’s a strong signal that consciousness may be emerging.”
Does that mean babies younger than five months are unconscious? Not necessarily: younger infants don’t display every sign at once, but some markers appear earlier. Intriguingly, similar signals can sometimes be detected in fetuses.
What are the main signs of a conscious brain?
One key sign neuroscientists point to is the default mode network — a group of brain regions active during rest, when people daydream, remember, or plan. Using functional magnetic resonance imaging (fMRI), researchers have found a simplified form of that network in newborns.
Another indicator is the so-called local–global effect. This effect reflects the ability to detect a change in a large pattern of stimuli, which signals working memory and perhaps conscious processing. For example, after many repetitions of a sequence, the brain begins to expect a final tone; if a new sequence breaks that learned pattern, the brain reacts even if no single element in the sequence deviates.
Frohlich sees traces of the local–global effect in newborns. And a team at the University of Tübingen found similar signs in fetuses late in pregnancy by measuring the magnetic fields generated by fetal brain activity with magnetoencephalography (MEG).
Light in the womb: can a fetus “see” faces?
Behavioral attention offers another potential sign of consciousness. Frohlich and Bayne say infants as young as four months can choose where to direct their attention. There’s also evidence that fetuses react to visual stimuli.
In 2017, Vincent Reid and colleagues at Lancaster University shone three points of light through the abdomen in a pattern resembling two “eyes” and a “mouth,” and they tracked fetal reactions with ultrasound. When the researchers moved the lights across the belly, fetuses turned their heads toward the light.
“No one knows for sure whether a fetus perceives something as a face or just as patches of light,” Frohlich says. Still, an independent team in Turin repeated the experiment and recorded fetal eye movements: the fetal eyes tracked the face-like light.
A theory of consciousness for artificial intelligence
Work by neuroscientists like Frohlich could reshape how we decide who or what counts as conscious. As artificial intelligence grows more sophisticated, Frohlich argues we should develop a theory of consciousness.
Understanding how and when human consciousness arises could provide a template for evaluating consciousness in nonhuman systems — from other animals to machines. But research continues, and many questions remain open.
Based on BBC Science Focus
Photo: Unsplash
