There is something obviously different in the brains of people with autism, and one of the chief symptoms of that is the difficulty they have in understanding other people's emotions and intentions.
But exactly what causes that is still being debated among neuroscientists -- and the debate only got sharper on Wednesday.
That's when scientists from New York and Pittsburgh published a study in the journal Neuron that concludes that one of the most prominent theories for what causes social problems in autism is flatly wrong.
The theory involves brain cells known as mirror neurons, which were first discovered in monkeys' brains about 15 years ago, and have since been identified in the human brain.
Mirror neurons are active not only when someone performs an action, like grabbing a cup, but when he sees someone else do the same thing.
That led to the idea that mirror neurons might be the basis of empathy -- understanding someone else's motives and goals -- and that notion was strengthened by some studies that seemed to show less activity in mirror neurons in people with autism.
The Neuron study, however, found just the opposite.