Abstract
IntroductionFunctional magnetic resonance imaging studies enable the investigation of neural correlates underlying behavioral performance. We investigate the effect of active and sham Continuous Positive Airway Pressure (CPAP) treatment on working memory function of patients with Obstructive Sleep Apnea Syndrome (OSAS) considering Task Positive and Default Mode networks (TPN and DMN).MethodsAn experiment with 4 levels of visuospatial n-back task was used to investigate the pattern of cortical activation in 17 men with moderate or severe OSAS before and after 2 months of therapeutic (active) or sub-therapeutic (sham) CPAP treatment.ResultsPatients with untreated OSAS had significantly less deactivation in the temporal regions of the DMN as compared to healthy controls, but activation within TPN regions was comparatively relatively preserved. After 2 months of treatment, active and sham CPAP groups exhibited opposite trends of cerebral activation and deactivation. After treatment, the active CPAP group demonstrated an increase of cerebral activation in the TPN at all task levels and of task-related cerebral deactivation in the anterior midline and medial temporal regions of the DMN at the 3-back level, associated with a significant improvement of behavioral performance, whereas the sham CPAP group exhibited less deactivation in the temporal regions of Default Mode Network and less Task Positive Network activation associated to longer response times at the 3-back.ConclusionOSAS has a significant negative impact primarily on task-related DMN deactivation, particularly in the medial temporal regions, possibly due to nocturnal hypoxemia, as well as TPN activation, particularly in the right ventral fronto-parietal network. After 2 months of active nasal CPAP treatment a positive response was noted in both TPN and DMN but without compete recovery of existing behavioral and neuronal deficits. Initiation of CPAP treatment early in the course of the disease may prevent or slow down the occurrence of irreversible impairment.
Highlights
Functional magnetic resonance imaging studies enable the investigation of neural correlates underlying behavioral performance
In spite of double-blind randomization procedure, the Continuous Positive Airway Pressure (CPAP) group had significantly higher BMI (p = 0.02) than the sham-CPAP group and tended to be more affected by Obstructive Sleep Apnea Syndrome (OSAS) as reflected by the PSG variables, even though the trend did not reach significance due to the large standard deviations present which was related to the limited number of studied subjects (Table 1)
In order to exclude the potential role of fatigue on brain activation and performance, we looked for a relation between response times (RT) during the 0-back epochs throughout both sessions of the n-back functional magnetic resonance imaging (fMRI) The activation/deactivation patterns in our healthy controls (HC) group mobilized cerebral regions previously described as involved during performance of WM tasks [19]
Summary
Functional magnetic resonance imaging studies enable the investigation of neural correlates underlying behavioral performance. Aspects of executive functions are consistently found impaired in behavioral studies on the impact of OSAS on cognitive function, but response to Continuous Positive Airway Pressure (CPAP) treatment varies [1,2]. With the advent of non-invasive neuroimaging techniques, such as functional magnetic resonance imaging (fMRI), it is possible to examine the neural correlates of cognitive performance as well as the individual impact of OSAS-related variables such as nocturnal hypoxemia and sleep fragmentation on brain function. Several fMRI studies conducted previously have reported both increased or decreased brain activation in OSAS patients These changes have been attributed to either a compensatory recruitment of brain resources in order to maintain performance or to brain damage secondary to nocturnal hypoxemia respectively [7,8,9,10,11,12]. TPN comprises several functional networks reported in cognitive literature such as the fronto-parietal attention network, executive network and right hemisphere-lateralized ventral frontal networks [13,14]
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