Asked by: Lily Stringer, St Andrews
What an impossible question! If I could answer it I would have solved a great philosophical puzzle - how activity in a brain can be 'about' something, such as wanting a strawberry ice cream or solving an equation. This is known as the problem of 'intentionality'.
We do know that brain areas are involved in thinking. For example, parts of the visual cortex at the back of your brain use more energy when you imagine seeing the ice cream, and parts of the sensory cortex when you think about its feel and taste. When you are doing mental arithmetic a different set of brain regions is involved, including areas in the parietal lobe, prefrontal cortex and cingulate, deep inside the brain. Although maths is popularly supposed to be a left-brain skill, both hemispheres are involved, with the left hemisphere more important when thinking about numbers as words.
These examples show that we can correlate brain activity with thinking, but we are a long way from fully answering your question.