In a study involving patients with epilepsy, the National Institutes of Health found how a set of high-frequency brain waves can help us observe these types of differences between past and present. The study was led by Rafi Haque, a doctoral student at the Emory University School of Medicine in Atlanta, who was completing his dissertation with Dr. Zaghloul. His main research goal was to test whether a theory called predictive coding can be applied to the way our brains remember past experiences, known as episodic memories. To test this idea, the team worked with 14 patients with drug-resistant types of epilepsy whose brains had been surgically implanted with electrode grids as part of a study by the NIH Clinical Center to diagnose and treat seizures. The experiment began when patients were shown and asked to memorize a series of four natural scenes displayed on a computer screen. For example, one of the scenes was a brown bicycle leaning upright on a kick stand in front of a green bush.