This is how the human brain differentiates between past and present

In a study of epileptic patients, National Institutes of Health discovered how a set of high-frequency brain waves can help us spot these differences between the past and the present. The study was led by Rafi Haque, MD, a PhD student at Emory University School of Medicine, Atlanta, who completed his dissertation work with Dr. Zaghloul. His main research goal was to test whether a theory called predictive coding can be applied to how our brains remember past experiences, called episodic memories. To test this idea, the team worked with 14 patients with drug-resistant epilepsy whose brains were surgically implanted with electrodes as part of a NIH Clinical Center trial aimed at diagnosing and treating their attacks. The experiment began when the patients were shown and asked to memorize a series of four natural scenes shown on a computer screen. For example, one of the scenes was of a brown bicycle leaning vertically on a kick in front of a green bush.

Source