A team of researchers from Cambridge University have demonstrated that whereas synaesthesia only occurred in 7.2% of typical individuals, it occurred in 18.9% of people with autism.
Synaesthesia describes the experience of a ‘mixing of the senses’, for example, seeing colours when you hear sounds, or reporting that musical notes evoke different tastes. Autism is diagnosed when a person struggles with social relationships and communication, and shows unusually narrow interests and resistance to change.
At the level of the brain, synaesthesia involves atypical connections between brain areas that are not usually wired together (so that a sensation in one channel automatically triggers a perception in another). Autism has also been postulated to involve over-connectivity of neurons (so that the person over-focuses on small details but struggles to keep track of the big picture).