Do newborn babies consciously hear sounds and feel pain? In the past, infant boys undergoing circumcision were often not given anaesthetic, partly because it was thought that their brains were immature and they couldn’t consciously feel pain. Even today, there remains much uncertainty. Babies cannot tell us what they are experiencing, so it is hard to know what they are conscious of.
Recently, neuroscientists have uncovered suggesting newborn infants perceive the world consciously. When newborns encounter certain surprising stimuli, their brain reacts strikingly similarly to the way conscious adult brains react.
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One method to investigate uses the oddball paradigm. First, you hear the same sound a few times in a row (like be-be-be). The next sound can either be another be or a different sound, like bo. When the final sound is different (be-be-be-bo), it surprises you because it breaks the pattern you were expecting, and your brain reacts with an electric signal, called the P300 wave, that reflects a violation of your expectations. This is known as a “local oddball” reaction.
In a more complex version, you hear a sequence like be-be-be-bo repeated several times and start expecting this pattern. If the sequence then changes to be-be-be-be, it surprises you again, and your brain again reacts with the P300 wave. This more complex change in the pattern is called a “global oddball” reaction.
In adults, local oddball reactions occur even when they are unconscious. Sleeping adults and comatose patients can produce the P300 wave in response to local oddballs. The more complex global oddball reaction, however, only happens when adults are conscious, not when they are sleeping or anaesthetised.
As a result, the global oddball P300 reaction is used as evidence of consciousness in those unable to communicate verbally. The task requires people to keep track of complex patterns, and tracking these patterns seems to require consciousness. If someone emerging from a coma shows the P300 response to global oddballs, this indicates they might be conscious.
Studies that 3-month-old infants have brain responses to global oddball stimuli, including a P300-like response. This suggests these infants detect both local and global oddballs. Another found similar responses in awake newborns in the first week of life. Insofar as global oddball detection is a sign of consciousness, these results suggest that newborns are conscious of the stimuli.
What about consciousness before birth? Researchers have also applied the oddball paradigm to measure brain responses in fetuses. One study fetuses after 35 weeks of gestation show a similar brain response to global oddballs. This suggests fetuses in the final weeks of gestation may be capable of consciously processing stimuli from outside the uterus. Any implications for the abortion debate are limited, as the results show evidence for consciousness only after 35 weeks, when abortions are very rare.
But there may be implications for areas such as infant care. If newborns can be conscious, they can also consciously experience pain. If so, they should receive anaesthesia for procedures such as circumcision. Similarly, if fetuses over 35 weeks of gestation can be conscious, we should take this possibility into account in fetal surgery and in childbirth to ensure appropriate pain management.
Infant consciousness is still poorly understood, but work like this shows it is possible to make progress. By applying insights from the science of consciousness in adults to infants, we may eventually have a scientific understanding of how infants experience the world.
Claudia Passos-Ferreira is a professor of bioethics at New York University
