How does brain imaging work and what does it mean for understanding our experiences?

Modern methods of analysing thought processes now involve special brain scanners called functional MRI (magnetic resonance imaging) and PET (positron emission tomography) scanners. These work upon the principle that brain cells have a constant need for blood, which carries with it all the vital nutritional substances that they need to work, including oxygen and glucose. So the scanners essentially detect and follow the movement of blood to various parts of the brain. This way they can tell us which part of the brain is working more actively at any time.

Watching one of these scanners can be analogised to using satellite technology, to observe the changes in the flow of water through water canals from space. A scientists would be able to tell which parts of the land were being worked on by agricultural workers at any one time simply by observing the changes in the flow of water in that region. In a similar way, brain scanners detect changes in the flow of blood to various regions of the brain, which in turn indicate which brain cells are working.

In addition to detecting changes in blood flow, specialized scanners can also detect the areas of the brain that have increased their consumption of oxygen and glucose. So by following the changes in flow of blood and the consumption of oxygen and glucose to various parts of the brain scientists can understand which areas of the brain are involved with certain thought processes. This is called 'mapping' the brain. To do this, scientists will place someone into a scanner and scan the brain while they are having certain thoughts.

Whatever we do and whatever conscious process we have, whether reading or listening to music, is accompanied by a reciprocal change in the pattern of blood flow to the part of the part of the brain involved with this sensation. If we really enjoy listening to our music and stop paying attention to other things, the areas that had been receiving more blood while will now receive less blood, but other areas will then start to receive more blood. Interestingly, brain scans have shown that for any thought many areas of the brain become active and that it is therefore multiple areas of the brain that mediate thought processes.

However, identifying blood flow changes or increased metabolism of certain parts of the brain, during an experience doesn't answer the big problem, which is: how does a physical collection of cells give rise to conscious experience? (see the mind brain problem). It also cannot detrmine if an experience is real or not (see Reality and NDE and Are religious experiences real?)