The brain area responsible for facial recognition may continue to grow well into adulthood, scientists have said. This is, however, not the case with the area of the brain that deals with recognising places – this remains largely the same for children and adults.
People's ability to recognise faces – a skill that is crucial to social interactions – improves from childhood to adulthood. Yet it is not entirely clear how cortical tissue changes as brain function and behaviour improve.
"Previous work done in our lab indicated that the brain continued to grow functionally as we age. People become better able to recognise faces, and we wanted to find out whether these functional changes were linked to structural changes", study author Jesse Gomez, from Stanford University, California, told IBTimes UK.
When a baby is born, the size of their brain is only round a quarter the size of an adult's. It grows to about 80% of adult size by three years of age and 90% by age five. Brain growth is mostly due to the growth of dendrites, the branching expansions of neurons that serve as the receiving point for input from other neurons.
Then, as we age, brain development is thought to involve 'synaptic pruning' rather than growth – we are born with an excess of neurons and as we grow, and the pruning process leaves us only with what's essential.
But this study, published in the journal Science, now shows that brain function and behaviour in adulthood may result from cortical tissue proliferation rather than from pruning exclusively.
Recognising faces and places
The scientists compared the brains of 22 children and 25 adults, and their performance at tests involving the recognition of faces and places. They used quantitative magnetic resonance imaging to compare brain tissue across individuals.
They found that the region of the brain that helps people recognise faces increases in relative size in adults compared with children, but not the area responsible for recognising places. "The total number of brain cells is not increasing, but cell bodies, dendritic structures and myelin sheath may increase. We observe microstructural proliferation in this small brain tissue", Gomez explained.
"You can think about it like a forest. In the small area of the brain responsible for facial recognition, the forest's acreage is not getting bigger, but the branches of the trees are – they are getting more complex with more connections".
The adults in the study were in their 20s, so more research in older participants may now be required to see if the kind of structural changes noticed here are also seen as people age.
Another area that would be interesting to investigate is why the area that deals with facial recognition changes while the area that is linked to place recognition does not. "We are unsure what the directional is here, but it could be that we are social animals and our brains need to change to adapt to the fact we need to recognise more and more people as we grow. It could also be that it is an area of the brain that is just much slower to develop, so it continues to do so in adulthood", Gomez concluded.