So what else can we do with this amazing technology? Well, it has been used experimentally to help us understand a number of brain functions. For example, in order to understand how choices are made, optogenetic techniques were used to switched on and off a flies??? preference for certain smells. This led to the amazing discovery of the fly???s inner critic, an assembly of 12 neurones that govern the decisions flies make. Scientists have also inserted light-responsive elements into more complex animals in an attempt to prove a causal relationship between certain groups of brain cells and a specific behaviour. In the video below, a mouse runs around every time a blue light is shone into its brain, meaning that the switching on of the light-activated brain cells causes the mouse to run. Another study made a mouse ???prefer??? to freeze on the spot by illuminating ??? and therefore activating ??? its reward centres every time it chanced upon a particular place in its cage. These experiments are elegant and powerful because they identify the particular set of brain cells that cause, or lead to some pretty complex actions.