Researchers from the Norwegian University of Science and Technology have been using electroencephalography (EEGs) to measure people's brain waves as they meditate. They found that during meditation theta waves were most abundant in the frontal and middle parts of the brain indicating a state of deep relaxation. Alpha waves - characteristic of wakeful rest - were more abundant at the back of the brain. There were fewer beta waves which are associated with conscious attention and problem solving.
You can find out more about this research at