Sleep abnormalities and memory alterations in obstructive sleep apnea

Objectives: Obstructive sleep apnea (OSA) is associated with a variable spectrum of sleep abnormalities and has been connected with memory impairment. The aim of this study was to evaluate the associations between OSA, memory alterations and sleep structure abnormalities. Methods: Polysomnography was performed in 20 consecutive patients (12 male, 57.9±5.8 years) with moderate/severe OSA (AHI 35.8±16.7). Daytime somnolence (Epworth Sleepiness Scale, ESS), state of alertness (Karolinska Sleepiness Scale), subjective sleep quality (Pittsburgh Sleep Quality Index, PSQI) and depressive symptoms (Beck Depression Inventory, BDI) were evaluated. Patients were tested before all night polysomnography and a retrieval test was performed in the following morning. Declarative memory was assessed by Verbal Paired Associates from the Wechsler Memory Scale, emotional memory by the exposure to emotional and non-emotional images and procedural memory by the maze test. Results: Excessive daytime sleepiness (ESS>10, 55%) and impaired sleep (PSQI>5, 40%) were found. Patients with OSA presented greater neck circumference (p<0.005). Procedural memory, as evaluated by the maze test, showed worse retrieval in OSA patients and this was maintained after controlling for age, body mass index and BDI. In subjects with moderate/severe OSA, stage 3 sleep was correlated to the performance in the procedural memory test. Conclusion: We show that procedural memory is altered in OSA patients as compared to controls and this alteration is related to stage 3 of non-rapid eye movement sleep. We confirm that recall memory tests after one night sleep are efficacious to examine memory abnormalities in OSA patients.