Abstract
Nearly all functional magnetic resonance imaging (fMRI) studies are conducted in the supine body posture, which has been discussed as a potential confounder of such examinations. The literature suggests that cognitive functions, such as problem solving or perception, differ between supine and upright postures. However, the effect of posture on many cognitive functions is still unknown. Therefore, the aim of the present study was to investigate the effects of body posture (supine vs. sitting) on one of the most frequently used paradigms in the cognitive sciences: the N-back working memory paradigm. Twenty-two subjects were investigated in a randomized within-subject design. Subjects performed the N-back task on two consecutive days in either the supine or the upright posture. Subjective sleep quality and chronic stress were recorded as covariates. Furthermore, changes in mood dimensions and heart rate variability (HRV) were assessed during the experiment. Results indicate that the quality of sleep strongly affects reaction times when subjects performed a working memory task in a supine posture. These effects, however, could not be observed in the sitting position. The findings can be explained by HRV parameters that indicated differences in autonomic regulation in the upright vs. the supine posture. The finding is of particular relevance for fMRI group comparisons when group differences in sleep quality cannot be ruled out.
Highlights
Neuroimaging investigations such as functional magnetic resonance imaging take place in an environment that is much different from a standard laboratory setting
We observed that general subjective sleep quality as measured by the Pittsburgh Sleep Quality Index (PSQI) correlates with reaction times (RTs) when the N-back task was performed in the supine position
This study demonstrates that poor quality of sleep can reduce cognitive performance in the supine posture without showing an effect in an upright posture
Summary
Neuroimaging investigations such as functional magnetic resonance imaging (fMRI) take place in an environment that is much different from a standard laboratory setting. Several factors like the confined space, scanner noise, or the uncontrollability of the situation have been shown to elicit anxiety and stress (e.g., MacKenzie et al, 1995), which in turn can affect behavioral and neural data (Muehlhan et al, 2013) Beside these environmental factors, the most important difference between a standard laboratory setting and neuroimaging investigations is body posture. Whereas non-imaging investigations of cognitive processes are usually performed sitting upright in front of a monitor, subjects are lying in supine position during fMRI scanning This essential difference has been discussed to affect physiological and psychological processes and renders comparisons of measurements inside and outside the scanner difficult (Raz et al, 2005; Duncan and Northoff, 2013). A more recent investigation has shown that the supine posture improves target
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