Neuropsychology of sleep and breathing: the effects of obstructive sleep apnea syndrome on cognition

Obstructive Sleep Apnea Syndrome (OSAS) is a common sleep disorder that has drawn the attention of neuropsychologists because of its possible deleterious effects on cognition. Several are the causes of the impairments this syndrome can produce, like fragmentation of sleep, intermittent nocturnal hypoxia and daytime sleepiness. Apolipoprotein E4 (APOE4) may also play a role in OSAS and it has been suggested as a trigger of cognitive impairment and of dementia-like patterns. This dissertation begins with a critical review of the literature, with the aim to provide the current overview of the main controversies about OSAS and its effects on brain and cognition. Three experimental studies aiming to shed light on the nature of the relationship between OSAS and cognition are then proposed. The first two studies focus on the effects of OSAS on information processing speed. Innovative measures have been proposed to clarify whether different components of information processing speed are impaired in OSAS (Study 1), and to evaluate the efficacy over time of the continuous positive airway pressure treatment (Study 2). Finally, Study 3 aims to evaluate the effects of APOE4 on psychometric performance, and to investigate at which sleep stage its presence could be a predictor of cognitive impairments in OSAS patients. Results show that OSAS is associated with impairment of the motor component of information processing speed, which can however be properly recovered after treatment. Furthermore, a retention memory deficit is reported in OSAS patients carrying APOE4, and NREM sleep fragmentation has been found to be directly involved in this impairment. This dissertation supports the hypothesis of a cognitive frailty associated with OSAS, however discouraging its irreversibility, and argues that APOE4 can be considered a risk factor for the memory loss observed in this syndrome.