Manipulating neural connections to see how they communicate and incite certain behaviors has eluded science until now. Researchers at the Max Planck Florida Institute for Neuroscience (MPFI) have invented a new tool, called Cal-Light, that can be used to observe and manipulate the neural activities underlying behavior and hopefully to identify causality between neuronal activity and behavior. Actively firing neurons receive an influx of calcium ions that can be painted with fluorescent dye to make them easier to watch. The new device combines this calcium imaging with recent optogenetics techniques and fluorescent gene expression. Once researchers identify a population of cells implicated in a particular activity using Cal-Light, they can use optogenetics in manipulating those cells. The researchers expect the device to help them dissect behaviors in a highly precise manner for the accumulation of evidence of causal relationships.