However, these methods do not allow to sample neurons at the level of networks. Any brain area is comprised of hundreds of thousands or millions neurons, and sampling one neuron at a time is impossibly slow. Last two decades have seen a revolution in technology that we can use to map the neuronal circuits and their function in the brain, and our laboratory has been at the forefront of these investigations. “Systems neuroscience”, which is the best way to describe our approach, allows us to record the activity of thousands of neurons simultaneously, within a specific brain area, or across brain areas, and to test the activity of any specific neuronal subtype or even just any specific neuron in a particular behavior.