Two components of long-term memory.

The existence of two independent components of long-term memory has been demonstrated by the authors. The evidence has been derived from the authors' findings related to the optimum spacing of repetitions in paired-associate learning. The two components are sufficient to explain the optimum spacing of repetitions as well as the spacing effect. Although the molecular counterparts of the two components of memory are not known, the authors provide a collection of guidelines that might facilitate identification of such counterparts.