The big dream for neuroscientists is to be able to watch our brain cells in action, in real time. Well, new research has maybe found the most promising tool yet - a technique to watch individual neurons light up in response to a stimulus, like flipping on a light switch. Scientists at the Max Planck Institute inserted a light-sensitive protein into a lab mouse. When a neuron fires, calcium ions flood through special cell channels. And when this light-sensitive protein binds to calcium, it radiates yellow light. So when the neuron fires it glows yellow. When scientists shot a puff of air at the mouse's whiskers, the brain cells in the sensory areas of the cortex glowed yellow. They watch this via thin glass fibers inserted into that brain region. With this technique scientists now have a way to watch single cell activity in many different regions of the brain at once. The hope is to investigate how the brain forms and loses neural connections during life experiences and when suffering from illnesses such as Alzheimer's, Parkinson's and schizophrenia.