Memory consolidation in fragmented sleep - N2 sleep spindles for verbal memory in patients with obstructive sleep apnea

Barner C, Ngo H-VV, Diekelmann S, Weeß H-G, Schlarb A. Memory consolidation in fragmented sleep - N2 sleep spindles for verbal memory in patients with obstructive sleep apnea. Somnologie. 2016;20(1):37-46.Background N2 sleep spindles have been frequently linked to sleep-dependent memory consolidation in healthy adults. Sleep spindles (9–15 Hz) increase during sleep after learning and correlate positively with the memory retention rate. Objectives As memory consolidation is impaired, but not completely absent, in patients suffering from obstructive sleep apnea (OSA), we tested whether learning affects N2 spindles in OSA patients. Materials and Methods We presented 91 word pairs to 18 patients with severe OSA (52 ± 2.28 years), asking one group (n = 9) to memorize them, while another group (n = 9) was prevented from learning. After a first recall in the evening (learning level) and a polysomnographically monitored night’s sleep, participants were tested again in the morning (recall level). N2 sleep spindle count and density were assessed for the whole night and for four consecutive sleep intervals of 90 min. Results N2 spindles did not significantly increase after learning in OSA patients. On a descriptive level, the spindle count at all electrode positions was higher after learning compared with the non-learning group for the whole night and for the first three 90 min intervals. Moreover, spindle scores only correlated with the memory retention rate in the learning group. Conclusion Despite the small sample size, these results provide a first hint toward the involvement of sleep spindles in memory consolidation in patients suffering from severe OSA. Memory consolidation in fragmented sleep. Available from: https://www.researchgate.net/publication/292186028_Memory_consolidation_in_fragmented_sleep [accessed May 3, 2017]