Fast sleep spindle (13-15 Hz) activity correlates with sleep-dependent improvement in visuomotor performance

Study Objectives: The relationship between memory enhancement and fast (13-16 Hz) versus slow (10-13 Hz) spindle activity during sleep was investigated. Design: Standard polysomnographic recordings were conducted during an adaptation, control nonlearning, and learning night. Automatic spindle detection and measurement was utilized with visual confirmation. Setting: Participants slept in individual, temperature-controlled bedrooms in a sleep laboratory. Participants: Twelve healthy student volunteers (9 women and 3 men, mean age: 22.3 years) participated. Interventions: On the learning night, participants completed a presleep learning session on a modified version of mirror-tracing task followed by a postsleep test session. No learning or test sessions were performed on the adaptation and nonlearning nights. Measurements and Results: Tracing time was reduced by 6.4 seconds (20.6% +/- 2.07%) from the presleep to the postsleep session. Mean amplitude and duration of fast spindles was greater on the learning night than on the nonlearning night (both P values < 0.05). Skill improvement and fast-spindle activity were positively correlated (density [r = 0.76, P < 0.01], amplitude [r = 0.69, P < 0.05], and duration [r = 0.67, P < 0.05]). Significant correlations between fast-spindle activity and mirror-tracing performance were also evident for the nonlearning night. There was no significant relationship between mirror-tracing performance and slow-spindle activity on any night. Conclusions: The thalamocortical network underlying fast-spindle generation may contribute to or reflect plasticity during sleep.