Epilepsy is one of the most common neurological disorders. According to the World Health Organization, it affects ≈50 million people worldwide at any given time, and ≈2% of the current world population has had epilepsy, has epilepsy now, or will experience it at some point in the future. In many patients epilepsy can be treated pharmacologically or through brain surgery, but a substantial subset of cases remains intractable, in part, because of our still incomplete understanding of the underlying causes of epilepsy. Determining how brains become seizure-prone and epileptic is therefore of vital importance for our understanding of this disorder, and could potentially enable the development of new treatment strategies.