Until we open our mouths to speak, it is possible for most of us to keep our thoughts to ourselves.
But computers could soon be able to predict what you are thinking by looking for distinct patterns of activity in your brain that relate to sentences.
Researchers have developed a computer program that is able to search for the brain activity related to certain words and then use this to predict a sentence being thought even it hasn't seen it before.
They say the system is able to get the predictions right around 70 per cent of the time.
Dr Andrew Anderson, a research fellow at the University of Rochester who is leading the study, said the technology could be used to help people who have suffered from a stroke to communicate.
He said: 'We found that we can predict brain activity patterns – not perfectly, but significantly better than chance.
'Not now, not next year, but this kind of research may eventually help individuals who have problems with producing language, including those who suffer from traumatic brain injuries or stroke.'
Stroke victims often suffer neuronal damage that hampers their control of the muscles that help them speak.
By looking for the brain activity related to words and sentences, they could communicate through a computer instead.
The researchers, whose study is published in the journal Cerebral Cortex, used brain scans taken with functional magnetic resonance imaging from 14 participants as they silently read 240 unique sentences.
For example, they read sentences like: 'The green car crossed the bridge', 'the magazine was in the car' and 'the accident damaged the yellow car'.
