(A) Episodic learning ability (% face-names encoded) in the Nap and Non-Nap group at 12:00 and 18:00 (left), and the change in episodic learning ability between sessions [18:00–12:00] (right). Episodic learning ability in a subset of Nap and No-Nap subjects (n=10 per group), matched on initial 12:00 performance, is presented in the center box. Comparisons (line across bars) in both plots reflect significance* at: P<0.05. Error bars represent s.e.m. (B) Within the Nap group, correlations with stage-2 NREM sleep and episodic learning ability at 12:00 (left-panel), 18:00 (middle-panel), and the change in learning ability between session [18:00–12:00] (right-panel). (C) Topographic correlations (color-bar indicates Pearson’s correlation strength) in the Nap-group between fast sleep spindles and episodic learning ability at 18:00 (post-nap), significant in derivations F3, F4, Fz, F7, F8, Fp1 and Fp2 over PFC, maximal at F7 (r=0.536, P=0.018). (D) Of these derivations, the change in episodic learning ability [18:00–12:00], significantly and conjointly correlated with fast-spindles at derivation F7 over left PFC (r=0.535, P=0.018). (E) sLORETA source time-series of fast sleep spindles identified by onset at F7, demonstrating a current-density loop recurring in left temporal lobe, proceeding the peak of the spindle. Spindle-time (ms) is presented below each cortical surface, relative to onset. A movie of this source time-series is provided in Supplemental Movie S1.