Abstract
Resting state fMRI (rs-fMRI) has recently been considered as a possible complement or alternative to task-based fMRI (tb-fMRI) for presurgical mapping. However, evidence of its usefulness remains scant, because existing studies have investigated relatively small samples and focused primarily on qualitative evaluation. The aim of this study is to investigate the clinical usefulness of rs-fMRI in the context of presurgical mapping of motor functions, and in particular to determine the degree of correspondence with tb-fMRI which, while not a gold-standard, is commonly used in preoperative setting. A group of 13 patients with lesions close to the sensorimotor cortex underwent rs-fMRI and tb-fMRI to localize the hand, foot and mouth motor areas. We assessed quantitatively the degree of correspondence between multiple rs-fMRI analyses (independent-component and seed-based analyses) and tb-fMRI, with reference to sensitivity and specificity of rs-fMRI with respect to tb-fMRI, and centre-of-mass distances. Agreement with electro-cortical stimulation (ECS) was also investigated, and a traditional map thresholding approach based on agreement between two experienced operators was compared to an automatic threshold determination method. Rs-fMRI can localize the sensorimotor cortex successfully, providing anatomical specificity for hand, foot and mouth motor subregions, in particular with seed-based analyses. Agreement with tb-fMRI was only partial and rs-fMRI tended to provide larger patterns of correlated activity. With respect to the ECS data available, rs-fMRI and tb-fMRI performed comparably, even though the shortest distance to stimulation points was observed for the latter. Notably, the results of both were on the whole robust to thresholding procedure. Localization performed by rs-fMRI is not equivalent to tb-fMRI, hence rs-fMRI cannot be considered as an outright replacement for tb-fMRI. Nevertheless, since there is significant agreement between the two techniques, rs-fMRI can be considered with caution as a potential alternative to tb-fMRI when patients are unable to perform the task.
Highlights
Accurate localization of functionally-relevant brain areas is important for presurgical planning, as it helps optimize resection and minimize postoperative neurological deficits
The 3 columns on the left denote the distance between the CoM of task-based functional MRI (fMRI) and that measured in the resting-state fMRI maps
Hemiplegia affecting the hemisoma contralateral to the side affected by the primary lesion and did not yield usable resting-state fMRI (rs-fMRI) data; further, rsfMRI maps from some aROI, fROI and ICA analyses were deemed un-informative and rejected
Summary
Accurate localization of functionally-relevant brain areas is important for presurgical planning, as it helps optimize resection and minimize postoperative neurological deficits. A possible alternative is localizing the motor cortex through its spontaneous activity This is a more recent approach which relies on the fact that spontaneous fluctuations in the blood oxygen level-related (BOLD) signal are temporally-coherent within discrete networks, that appear to correspond to specific brain circuits involved in motor control, vision and cognitive integration [15]. In their seminal study, Biswal et al [16] demonstrated that under wakeful rest the BOLD signal fluctuations of the left and right sensorimotor cortex and supplementary motor area are correlated, leading to the notion of a sensorimotor resting-state network. Further work on healthy controls has demonstrated that topographical maps obtained via resting-state fMRI (rs-fMRI) are highly consistent and reproducible across subjects and sessions [17,18,19], and that tb-fMRI and rsfMRI yield moderately consistent results in healthy controls [20,21,22]
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