What is the principle of long-term potentiation, and how might experience (exposure to info, practice, etc.) impact long-term memory?

Very briefly explain the primary findings of the Yang et al. (2006) study on plasticity in memory in late life.  Be sure to address between-subjects (separate groups) and within-subject (same people measured repeatedly) results.

Please use “Basic Forms of Cognitive Plasticity Extended Into the Oldest-Old: Retest Learning, Age, and Cognitive Functioning” (Yang et al. 2006) as reference. (ONLY).