Babies' 'busy' brains create new knowledge even while sleeping

It might look like all what babies did was eat, sleep and cry, but in reality their brains are constantly working and creating new knowledge even while they sleep.

Scientists from the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig worked with the researchers from the University of Tubingen, and discovered that babies of the age from 9 to 16 months remember the names of objects better if they had a short nap. And only after sleeping could they transfer learned names to similar new objects. The infant brain thus forms general categories during sleep, converting experience into knowledge.

The researchers also showed that the formation of categories is closely related to a typical rhythmic activity of the sleeping brain called sleep spindles: Infants with high sleep spindle activity are particularly good at generalizing their experiences and developing new knowledge while sleeping.

Sleep means much more than just relaxation for our brain. The flow of information from the sensory organs is largely cut off while we sleep, but many regions of the brain are especially active. Most brain researchers today believe that the sleeping brain retrieves recent experiences, thereby consolidating new knowledge and integrating it into the existing memory by strengthening, re-linking or even dismantling neuronal connections. This means that sleep is indispensable for memory.

The analysis of brain activity showed that the infants had learned the names of the individual objects during the training session, irrespective of their age. The situation with categorization, however, was different: At the end of the training session, they were unable to assign new objects to the names of similar objects which they had heard several times.

During the subsequent testing session, the brain activity of the infants who had slept after the training session was markedly different from that of the group who had stayed awake. While the group who had stayed awake had forgotten the names of the individual objects, the children in the sleep group remembered the object-word mappings. There were also radical differences in their abilities to categorize the objects.

While the children's age had no effect, a particular type of brainwave called the sleep spindle has a significant impact on learning outcomes. "The greater an infant's spindle activity, the better it can assign category names to new objects after sleep", explained Manuela Friedrich.

Head of the study Angela Friederici, Director at the Max Planck Institute said that the waking infant brain quickly forgets newly learned names, but during sleep, words are more durably linked to objects and imprinted.