Abstract
Except for task-specific functional MRI, the vast majority of imaging studies assessed human brain function at resting conditions. However, tracking task-specific neuronal activity yields important insight how the brain responds to stimulation. We specifically investigated changes in glucose metabolism, functional connectivity and white matter microstructure during task performance using several recent methodological advancements. Opening the eyes and right finger tapping had elicited an increased glucose metabolism in primary visual and motor cortices, respectively. Furthermore, a decreased metabolism was observed in the regions of the default mode network, which allowed absolute quantification of commonly described deactivations during cognitive tasks. These brain regions showed widespread task-specific changes in functional connectivity, which stretched beyond their primary resting-state networks and presumably reflected the level of recruitment of certain brain regions for each task. Finally, the corresponding white matter fiber pathways exhibited changes in axial and radial diffusivity during the tasks, which were regionally distinctive for certain tract groups. These results highlight that even simple task performance leads to substantial changes of entire brain networks. Exploiting the complementary nature of the different imaging modalities may reveal novel insights how the brain processes external stimuli and which networks are involved in certain tasks.
Highlights
Non-invasive neuroimaging techniques provide us with the opportunity to characterize the human brain at multiple levels of structure and function
Except for the supplementary motor area (SMA) and contralateral M1, none of the regions identified with functional connectivity during the tasks were part of their primary resting-state networks (Smith et al 2009)
None of these regions showed relevant changes in cerebral metabolic rate of glucose (CMRGlu) (Fig. 3a), indicating that functional connectivity and glucose metabolism may change independently and represent complementary information (Wehrl et al 2013), which cannot be captured by one imaging modality alone
Summary
Non-invasive neuroimaging techniques provide us with the opportunity to characterize the human brain at multiple levels of structure and function. Except for functional magnetic resonance imaging (fMRI), the vast majority of studies assessed such imaging parameters at rest, mostly comparing patient cohorts to healthy controls These investigations have demonstrated fundamental insight into the human brain and alterations thereof, task-relevant image acquisition yields specific information how the brain processes and responds to external stimulation, which in turn can be directly linked to performance and behavior. Task-relevant functional connectivity has often been computed from conventional fMRI approaches (Honey et al 2002; Fair et al 2007), despite the fact that these were designed to study neuronal activation in response to 10–20 s stimulation instead of connectivity across several minutes Such approaches include disadvantages in terms of high-frequency signal changes between rest and task, which may in turn cause pronounced differences in connectivity as compared to continuous acquisitions (Ganger et al 2015)
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