Lag effect

Biological Parallel

Memory strengthens most when reactivation occurs after partial forgetting—the spacing effect appears across biological scales. Honeybees conditioned with 10-minute intervals between trials form protein-synthesis-dependent late long-term memory; 1-minute intervals produce only transient early memory. Bumblebees show the same pattern, improving associative learning when trial intervals increase. Vaccine boosters spaced beyond 38 days generate higher antibody titers than shorter intervals—longer gaps force the immune system to actively reconsolidate rather than merely top off existing responses. During sleep, hippocampal neurons replay learned patterns at the forgetting threshold, transferring memories to cortical storage through coordinated oscillations between slow waves, ripples, and spindles. The computational principle is universal: optimal spacing challenges the system enough to trigger consolidation without complete erasure. Too soon provides no adaptive pressure; too late requires starting from scratch.