Brain learns to recognise faces through repeated exposure

Regions of the brain that are key to facial recognition form only through experience, says a new study that casts doubt on the longstanding belief that the ability to recognise faces must be innate for people and other primates.

The study, published in the journal Nature Neuroscience, showed that those brain regions for social recognition were absent in primates who did not encounter faces while growing up.

The findings suggest that sensory deprivation has a selective effect on the way the brain wires itself. The brain seems to become very good at recognising things that an individual sees often, and poor at recognising things that it never or rarely sees, said Margaret Livingstone, Professor of Neurobiology at Harvard Medical School.

"What you look at is what you end up 'installing' in the brain's machinery to be able to recognise," she added. The finding, the researchers said, sheds light on a range of neuro-developmental conditions, including those in which people cannot distinguish between different faces or autism, marked by aversion to looking at faces.

Most importantly, however, the study underscores the critical formative role of early experiences on normal sensory and cognitive development, the scientists said.

To better understand the basis for facial recognition, the researchers raised two groups of macaques -- a close evolutionary relative to humans, and a model system for studying human brain development .

The first one, the control group, had a typical upbringing, spending time in early infancy with their mothers and then with other juvenile macaques, as well as with human handlers.

The other group grew up raised by humans who bottle-fed them, played with and cuddled them -- all the while the humans wore welding masks. For the first year of their lives, the macaques never saw a face -- human or otherwise. At the end of the trial, all macaques were put in social groups with fellow macaques and allowed to see both human and primate faces.

When both groups of macaques were 200 days old, the researchers used functional MRI to look at brain images measuring the presence of facial recognition patches and other specialised areas, such as those responsible for recognising hands, objects, scenes and bodies.

The macaques who had a typical upbringing had consistent "recognition" areas in their brains for each of these categories. Those who had grown up never seeing faces had developed areas of the brain associated with all categories except faces, the study said.