As a baby develops, the brain undergoes a burst of synapse formation, the connections between different nerves. Then, over time, these synapses are "pruned" back, retaining the necessary ones.
My guess is that this may be related to why it is easier for someone who hears, and learns to speak, a language when they are young rather than when they are older. The connections are all there, but as someone ages they are lost.
The Columbia University scientists examined the brains of 26 autistic children and young people aged two to 20 who had died from a variety of causes
By late childhood, the researchers found that spine density had dropped by about half in the healthy brains, but by only 16 per cent in the brains of autistic individuals.
Lead researcher Professor David Sulzer said: ‘It's the first time that anyone has looked for, and seen, a lack of pruning during development of children with autism, although lower numbers of synapses in some brain areas have been detected in brains from older patients and in mice with autistic-like behaviours.'
He added: ‘While people usually think of learning as requiring formation of new synapses, the removal of inappropriate synapses may be just as important.