February 13, 2006 Everyone knows about brain scanning, but most of us have never heard of a new technology called transcranial magnetic stimulation (TMS). Non invasive and painless, it can temporarily inactivate an area of the human brain to let brain scientists study the effect. Twenty years ago we began the scientific dream of peering into the human brain while it is working. Brain scanning devices such as fMRI and PET scans can pinpoint precisely which brain regions are active as people respond to stimuli (including brands and advertisements) or as they go about making decisions (including brand choices). It is fascinating to see just what areas of the brain light up in response to a stimulus or a particular decision task but still we have to ask, what exactly can we conclude from this? Because an area of the brain lights up doesn’t mean that it is causal in that behaviour or decision. After all, ice cream sales correlate with drownings but they don’t cause them. You cannot conclude causality from correlation because there is no way of knowing if some other, unaccounted-for variable (like weather) may be involved. To sort out causality you need to be able to do experimentation.