In a study involving epilepsy patients, the National Institutes of Health has discovered how a set of high-frequency brain waves may help us spot these kinds of differences between the past and the present. The study was led by Rafi Haque, an M.D., Ph.D. student at Emory University School of Medicine, Atlanta, who was completing his dissertation work with Dr. Zaghloul. His primary research goal was to test out whether a theory called predictive coding can be applied to how 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 grids of electrodes as part of an NIH Clinical Center trial aimed at diagnosing and treating their seizures. The experiment began when the 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 of a brown bicycle leaning upright on a kickstand in front of a green bush.