Thoughts consist of more than words
When we think about familiar objects such as a hammer, the thought does not only cause activity in the language centres of the brain. It produces a specific activity pattern in several brain regions, which process actions related to the object. The word hammer discharges neurons in the frontal lobes, which have to do with motor functions, as the word makes us think about how to hold a hammer, etc. By decoding the pattern, scientists can read our minds.