This involves shining a light into the brain to discern how much activity is there, and examining the corresponding oxygen level.

CNN: Brain-controlled devices may help paralyzed people

To study the neurology of tickling, Dr Blakemore and her team stuck volunteers into a magnetic-resonance-imaging machine (which monitors oxygen flow to the brain, and thus indicates the amount of activity in that organ's various parts).

ECONOMIST: Neuroscience: Tickled curiosity | The

By contrast, modest black-hole activity can stir things up and encourage the formation of the kinds of elements (carbon, oxygen and so on) that are essential for life as we know it.

WSJ: Book Review: Gravity's Engines