Association between default‐mode network and medial temporal lobe functional connectivity and episodic memory in late middle‐aged and older patients with obstructive sleep apnea

Abstract Background Obstructive sleep apnea (OSA) is associated with risk of cognitive decline in older adults. Our group previously observed that more severe OSA was associated with lower functional connectivity between the hippocampus and multiple regions of the default‐mode network (DMN) and the limbic system. However, whether these lower functional connectivity is associated with memory impairment is unknown. Here, we tested the hypothesis that lower functional connectivity previously associated with OSA severity could be related to worse episodic memory performance in late middle‐aged and older adults. Method We included 37 participants with moderate‐to‐severe OSA (apnea‐hypopnea index [AHI] : 33±18 events/h, 7 females, 67.2±7 years old, 15.2±3.4 years of education, 15 with mild cognitive impairment [MCI]) and 59 control participants (AHI: 5.8±3.7 events/h, 18 females, 65±6.9 years old, 15.5±3.3 years of education, 25 MCI) matched for age, sex, education and cognitive diagnosis. They underwent a neuropsychological assessment, a full‐night of polysomnography and a resting‐state functional magnetic resonance imaging. A composite score for episodic memory performance was calculated with the Rey Auditory Verbal Learning Test (trials 1 to 5, immediate and delayed recalls) and the Brief Visuospatial Memory Test‐revised (total and delayed recalls). CONN toolbox was used to perform multiple regression analyses between resting‐state functional connectivity and memory performance for each group separately. All analyses were controlled for age, sex and education, and corrected for false‐discovery rate. Result In OSA participants, lower functional connectivity between the medial prefrontal cortex and the hippocampus was associated with better episodic memory performance (ps<0.05), while a trend was observed in the control group (p = 0.05). Lower functional connectivity between the lateral parietal cortex and the parahippocampus was also associated with better episodic memory performance in the OSA participants (p = 0.03). Conclusion Contrary to our hypothesis, the lower resting‐state functional connectivity observed in OSA participants was associated with better episodic memory performance. This pattern of functional connectivity between the DMN and the limbic system negatively associated with episodic memory performance was previously reported in healthy older adults and patients with preclinical Alzheimer’s disease. Whether these functional connectivity patterns predict further cognitive decline in untreated OSA patients needs to be investigated.