Early signs of autism can be detected in babies by playing peek-a-boo, research has shown.
If their brains respond less than they should to the stimulating game they are more likely to be diagnosed with an autism spectrum disorder (ASD) as toddlers.
Scientists used neuroimaging technology to compare the brain activity of infants faced with social and non-social stimuli.
Social stimuli included games such as peek-a-boo, yawning and laughter. An example of non-social stimuli was looking at pictures of cars.
Low levels of response to social stimulus relative to non-social stimulus indicated a greater risk of having autism as a toddler.
The research is the first to show that functional brain responses before the age of six months are associated with later ASD diagnosis.
Study leader Dr Sarah Lloyd-Fox, from Birkbeck, University of London, said: "We have found an early indication of different patterns of brain activity in infants who go on to develop ASD.
"Given the importance of responding to others in our social world, it is possible that different attentional biases in babies may impact on the development of social brain responses, which can continue to affect the child's developmental trajectory as they get older."
Autism, characterised by an impaired ability to communicate and interact socially and repetitive behaviour, affects around 2.8 million people in the UK.
Early symptoms of the developmental disorder are known to emerge in toddlers, but little is known about how the condition develops in the first months of life.
Dr Lloyd-Fox said: "Identifying early patterns of altered development which may later associate with ASD is important, because it will allow doctors to offer earlier interventions and provide families with earlier avenues for support.
"This might mean giving the child and parents new strategies to reengage their attention towards important social cues and learn different ways of interacting."
The research is published in the European Journal of Neuroscience.
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