The concept of stimulus-specific memory traces, or engrams, suggests that the fate of
individual memories can be tracked via empirically observable brain states. Recent
advances in neuroscience have made it possible to discern these brain states in various
ways. In animals, transgenics and optogenetics have allowed identifying distinct cell
populations as engrams, which are necessary and sufficient for specific memory contents. In
humans, individual memories have been associated with unique brain patterns via …