Intact implicit probabilistic sequence learning in obstructive sleep apnea

Obstructive sleep apnea (OSA) belongs to the sleep-related breathing disorders and is associated with cognitive impairments in learning and memory functions. The impairments in attention-demanding cognitive functions such as working memory and executive functions are well established in OSA; however, it remains unknown if less attention-demanding implicit sequence learning is affected. In the present study, we examined implicit sequence learning in OSA to probe the functional integrity of this fundamental learning mechanism. We used listening span to measure complex working memory capacity and the alternating serial reaction time (ASRT) task, which enables us to measure general skill learning and sequence-specific learning separately. Twenty OSA patients and 20 healthy controls participated in this study. Our data show dissociation between working memory and implicit sequence learning in OSA. Surprisingly, OSA patients showed preserved general skill and sequence-specific learning in spite of the possible hypoxia and sleep restriction. In contrast, working memory performance measured by listening span task was impaired in the OSA group. This finding suggests selective susceptibility of more attention-demanding cognitive functions in this patient population, while implicit learning remains intact. Our findings draw attention the fact that disordered sleep may have less impact on the integrity of structures connected to implicit sequence learning.