Abstract
BackgroundDisruption of the default-mode network (DMN) in healthy elders has been reported in many studies.MethodsIn a group of 51 participants (25 young, 26 elder) we examined DMN connectivity in subjects' native space. In the native space method, subject-specific regional masks (obtained independently for each subject) are used to extract regional fMRI times series. This approach substitutes the spatial normalization and subsequent smoothing used in prevailing methods, affords more accurate spatial localization, and provides the power to examine connectivity separately in the two hemispheres instead of averaging regions across hemispheres.ResultsThe native space method yielded new findings which were not detectable by the prevailing methods. The most reliable and robust disruption in elders' DMN connectivity were found between supramarginal gyrus and superior-frontal cortex in the right hemisphere only. The mean correlation between these two regions in young participants was about 0.5, and dropped significantly to 0.04 in elders (P = 2.1 × 10−5). In addition, the magnitude of functional connectivity between these regions in the right hemisphere correlated with memory (P = 0.05) and general fluid ability (P = 0.01) in elder participants and with speed of processing in young participants (P = 0.008). These relationships were not observed in the left hemisphere.ConclusionThese findings suggest that analysis of DMN connectivity in subjects' native space can improve localization and power and that it is important to examine connectivity separately in each hemisphere.
Highlights
The existence of coherent blood-oxygen-level-dependent (BOLD) signal in the lower frequencies among different brain regions at rest is commonly reported (Raichle 2009)
The black dots show the means of the groups, the single asterisk is indicative of significant difference with 0.00056 < P < 0.05, and the double asterisks is the indicative of significance level after Bonferroni correction P < 0.00056
Only the agerelated difference in functional connectivity between supramarginal gyrus (SM) and superior-frontal gyrus (SF) in the right hemisphere remained significant after Bonferroni correction (P = 0.000021)
Summary
The existence of coherent blood-oxygen-level-dependent (BOLD) signal in the lower frequencies among different brain regions at rest is commonly reported (Raichle 2009). Spatial normalization is the conventional method for warping all subjects in a study into a standard space and facilitates the use of predefine regions-of-interest (ROI) mask from the utilized brain atlas instead of the subjects own regional mask. It is implemented by registering each subject’s brain to a canonical template brain. In the native space method, subject-specific regional masks (obtained independently for each subject) are used to extract regional fMRI times series This approach substitutes the spatial normalization and subsequent smoothing used in prevailing methods, affords more accurate spatial localization, and provides the power to examine connectivity separately in the two hemispheres instead of averaging regions across hemispheres. Conclusion: These findings suggest that analysis of DMN connectivity in subjects’ native space can improve localization and power and that it is important to examine connectivity separately in each hemisphere
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