Declan Murphy and his colleagues at King’s College London used a functional MRI scanner to watch how babies’ brains responded to sounds while they slept. The group used a modified scanner quiet enough to scan 21 infants aged between 3 and 7 months without waking them.
Murphy’s team first compared the babies’ responses to human non-verbal vocalisations â€“ such as coughs and sneezes â€“ and other sounds that the tots would be familiar with, like the sounds produced by a musical toy. They found that different regions of the babies’ brains responded more strongly to the different stimuli in the same way that an adults’ awake brain does.
The group then played the sleeping infants sad, neutral and happy human vocalisations, which included the sounds of crying and laughter. In all cases the scans revealed significant activity in several brain regions including the middle temporal gyri, right lingual gyrus and medial frontal gyri â€“ such patterns of activity are seen when adults who are awake listen to such sounds.
While the babies’ brains responded in a similar way to both happy and neutral sounds, sad sounds â€“ such as the sound of crying â€“ resulted in stronger activation in regions of the brain called the insular cortex and gyrus rectus. This pattern of activity is also seen when adults who are awake hear sad sounds.
“It’s fascinating that they can do this,” Murphy says. “You’d think that a sleeping baby wouldn’t be able to hear you, but clearly their brains are processing sounds while they’re asleep.”
The finding might send a chill down the spine of all parents that have engaged in a whispered argument over a sleeping child, but Murphy points out negative sounds might not necessarily be detrimental for the baby. “It could be a good thing â€“ the brain could be training itself to respond to these sounds,” he says.
The reason why sleeping babies tune in to the sounds around them remains a mystery. “It could be because they are hard-wired to be alert,” Murphy suggests. Emanuel DiCicco-Bloom, who researches child neurology at Robert Wood Johnson Medical School in Piscataway, New Jersey, agrees. “This might mean that certain brain regions needed for survival are already specialised very early, and are less dependent on extensive postnatal experience,” he says, adding that babies may even learn to distinguish such sounds through eavesdropping on the outside world while still in the womb.
Murphy hopes his continuing research will provide insight into social communication, and how problems in processing emotional speech develop in autism. “If we’re going to understand how people develop abnormal processes, we need to understand normal development.”
The team has begun to look at the brains of young infants with older autistic siblings. Such infants are known to have about a 20 per cent chance of developing the disorder.
“We need to see what’s happening before autism develops,” says Murphy. His team also hopes to be able to monitor the progress of at-risk children who do not go on to develop autism in order to identify protective factors in their lifestyles.