Even in the mother’s body, the human brain receives information and processes it. If a baby is born, it can see, hear and respond to touch. However, all these functions are not yet fully developed. As a result of perception and experience, the number of connections between the nerve cells increases rapidly in the first three years of life. At two years the amount of synapses corresponds to that of adults; A three-year-old has twice as many as 200 trillion. Up to the age of the child, about half of them will be dismantled again, until the amount of 100 trillion typical for adults is reached. It has hitherto been assumed that a large part of the brain development and plastic adaptation to living conditions in children is the reduction of the synapses which are not relevant to their life, the so-called “pruning” or “thinning”.
The scientists studied the functional organization and microscopic structure of brains of children and young adults for several months. The children in the study were between 5 and 12 years of age, the adults between 22 and 28 – an age where the structural and functional development of the so-called temporal lobes, a part of the cerebrum, had been considered complete. They focused on a particular brain region, the so-called gyrus fusiformis, which contains, among other things, important structures for cognitive functions such as facial and word recognition, but also for the recognition of certain spatial aspects as well as for symbols (eg letters).
All the participants looked at a series of pictures: faces, bodies, places, objects and symbols. By means of functional magnetic resonance tomography, the researchers identified the areas of the brain with the greatest specific activity for these stimuli. Thus, they localized two neighboring brain regions: one recognizes places with the other faces.
Only adults can remember faces well
A comparison of the data showed additional tissue in adults – but only in one of the two brain regions, the one for facial recognition. The researchers hypothesized that the growth of the so – called dendritic cell extensions of the nerve cells, which predominantly serve to stimulate the irritation, is responsible for the additional tissue. “Dendrites collect information from different brain regions and bring them to the individual nerve cells,” explains Karl Zilles, JARA Senior Professor at the Jülich Institute of Neurosciences and Medicine and the Department of Psychiatry at RWTH Aachen University. “We think that the dendrites and synapses as well as the myelin around the existing axons of the nerve cells develop strongly in the region for facial recognition.”
The ability to recognize faces is not yet fully developed in children. It is developed in the course of growing up. The scientists also checked this assumption. They subjected the children and adults to two different tests to determine how well they could recognize faces and places. For face recognition, they used a variant of the so-called Cambridge Face Memory test. It tests the ability to recognize once-seen faces under increasingly difficult conditions, such as pairing with similar faces, other light conditions, or superimposed image distortions. While the original form of the Cambridge test works with faces of adult men, pictures of children ‘s faces were used here, as it is more difficult for young test subjects to keep faces from adults apart. A similar test was used for the location recognition, in which houses and corridors were recognizable.
Children were similar in both tests. It was different with adults. “They were able to remember impressed faces much better than places,” explains Katrin Amunts. “This supports the hypothesis that facial recognition is an ability that is still developing in the youth age.” This development is closely related to the growth of dendrites, synapses and myelin in the corresponding region of the temporal lobe. “In the cerebral area for facial recognition, tissue growth was demonstrated, but not in the area for location detection, which is in perfect agreement with the functional findings,” notes Karl Zilles.
Similar growth processes are also to be expected in other areas, according to Amunts – for example, in the language center. “Finally, the language skills develop over a relatively long period of time.” The present publication thus shows for the first time a regional and function-specific growth of certain but not all brain regions in the period between childhood and adulthood.