My laboratory is studying the neuronal circuitry of the cerebral cortex. More than any other part of the brain, the cerebral cortex is what makes us human; it is the site of our highest mental capacities such as learning, language and consciousness itself. When ravaged by epilepsy, trauma, stroke or age-related degeneration, the consequences are devastating to the individuals afflicted and to their families. The cerebral cortex is a vast neuronal network in which an astronomically large number of neurons, with a large variety of shapes, electrical properties and chemistries, make an even larger number of connections (synapses) with each other. The cortical "wiring diagram," the precise patterns of connections between neurons, is the basis for its amazing computational capacities; but, this wiring diagram is still, by and large, unknown. To begin to decipher it, we are recording from pairs of neurons in mouse brain slices in vitro. We use several transgenic mouse lines, some of which we have developed ourselves, in which specific populations of cortical neurons express fluorescent proteins, and are therefore identifiable under a microscope and can be targeted by recording microelectrodes (see image below). To understand how these neuronal subsets and the networks they form give rise to animal (and human) behavior, we are beginning to record from brains of intact, awake animals, while activating or inactivating specific subsets of neurons by light, a technique known as "optogenetics." In planning are also experiments in which we will use optogenetics in freely behaving animals.