epilepsy

Roughly two-thirds of the general population reports experiencing déjà vu at some point in their lives — that disorienting conviction that a present moment has been experienced before, accompanied by the simultaneous knowledge that it cannot have been. The experience lasts a few seconds, then dissolves. For most people it is occasional and benign. For patients with temporal lobe epilepsy, it can be a reliable seizure precursor. The fact that déjà vu can be reproduced reliably in clinical settings — both by electrical stimulation of specific brain regions and by certain drug compounds — tells neuroscientists where to look for the mechanism.

How Hans Berger's secret obsession with telepathy in 1924 produced the EEG—and why those squiggly lines still diagnose epilepsy and decode sleep 100 years later.

Why does déjà vu happen? Neuroscience explains the memory mismatch, dual-processing, and temporal lobe theories behind the 'already seen' feeling.