Relationship between obstructive sleep apnea severity and brain activation during a sustained attention task

Abstract

Study objectives: The objectives of this study were to (1) characterize cognitive and cerebral correlates of attention and response speed in patients with obstructive sleep apnea (OSA) and (2) assess the association of performance and brain activation with measures of OSA severity.

Design: Patients with OSA and controls were compared on performance and brain activation during a sustained attention task. The association of reaction time and brain activation with apnea-hypopnea index, nocturnal hypoxia, and arousals was assessed.

Setting: Functional magnetic resonance imaging was conducted while participants performed a Go-No-Go task. The 'Go' trials of the Go-No-Go task were used to index attention processing.

Participants: Fourteen patients with OSA and 14 normal control subjects with equivalent age, body mass index, blood pressure, and education.

Interventions: N/A.

Measurements and results: Patients with OSA showed decreased brain activation in cingulate, frontal, and parietal regions typically involved in attention tasks, compared with control subjects. Within the patients with OSA, increasing arousal index, but not desaturation index, was associated with slower mean reaction time and with decreased brain activation in areas involved in arousal and attention, response selection, motor response, and decision making. The apnea-hypopnea index, by itself, was not associated with changes in cerebral response.

Conclusions: Patients with OSA showed decreased brain activation compared with control subjects during an attention task. The association of arousal index (but not hypoxia) with slow reaction times and brain activation suggests that alertness and reaction times show greater correlations with measures of sleep disruption than with measures of hypoxia.

Figure 1

Brain regions showing significant group differences (obstructive sleep apnea [OSA] minus control) in activation during the Go trials (See Table 4). In all clusters showing group differences, the OSA group exhibited decreased responses (light blue, smallest differences; dark blue, largest). The panel shows sagittal slices from left to right. Numbers correspond to Talairach and Tournoux coordinates of the sagittal slices (L: left, R: right). For all images, clusters surviving our cluster threshold method are overlaid in color on top of the group average anatomic image. The color corresponds to the effect-size eta, corresponding to the amount of variance accounted for by group membership. A: left precentral gyrus, inferior parietal; B: Left precentral gyrus; C: Left insula, precentral gyrus, inferior parietal lobe; D: left middle frontal gyrus, superior parietal, posterior cingulate; E: left medial frontal gyrus, cingulate gyrus; F: right insula.

Figure 2

Relationship between arousal index and mean reaction time (Avg Go RT) in the obstructive sleep apnea (OSA) group, after removing the influence of age. The x-axis shows each subject's mean RT, and the y-axis shows the residual of the arousal index (partialing out the effect of age).

Figure 3

Brain regions showing significant correlations with arousal index during the Go trials (See Table 5). In all clusters showing correlations with arousal index, increased arousal index was associated with smaller brain responses. The panel shows sagittal slices and axial slices with numbers corresponding to Talairach and Tournoux coordinates (L: left, R: right, S: superior). For all images, clusters surviving our cluster-threshold method are overlaid in color on top of the group-average anatomic image. The color corresponds to the effect-size eta, corresponding to the amount of variance accounted for by arousal index. A: left precentral gyrus; B: left middle frontal gyrus, insula, parahippocampal gyrus; C: bilateral superior frontal gyrus; D: right middle frontal gyrus; E: right insula, middle frontal gyrus; F: right inferior frontal gyrus; G: right lentiform nucleus, lateral globus pallidus; H: left thalamus.