The Forgetting Curve
Ebbinghaus (1885) · FSRS spaced repetition
A memory decays as R = e−t/S. Turn on spaced repetition and watch each review reset the curve — so retention stays high with a fraction of the storage.
Hebbian Learning
“Neurons that fire together, wire together”
When two memories are recalled together, the edge between them strengthens (asymptotically toward a cap). Left idle, it decays — and is pruned when too weak.
Sleep Consolidation
Stickgold & Walker (2013) · memory replay
During sleep the hippocampus replays recent memories — important and emotional ones are strengthened, weak connections are pruned. Press sleep and watch it happen.
Calibrated Confidence
Bayesian confidence intervals
ZenBrain never returns a bare number. Every estimate carries a 95% confidence interval that narrows as evidence accumulates — few reviews mean honest, wide uncertainty.