Behavioral deficits in left hemispatial neglect are related to a reduction of spontaneous neuronal activity in the right superior parietal lobule

Focal brain lesions may induce dysfunctions in distant brain regions leading to behavioral impairments. Based on this concept of ‘diaschisis’, spatial neglect following stroke has been related to structural damage of the right-lateralized ventral attention network (VAN) and disrupted inter-hemispheric functional connectivity (FC) in the bilateral dorsal attention network (DAN). We questioned whether neglect-related behavioral deficits may be determined by local dysfunction of a specific region within these brain networks. We investigated acute right-hemisphere stroke patients with left hemispatial neglect using resting-state functional MRI, neuropsychological tests of spatial attention and clinical assessment of neglect-related functional disability. In addition to conventional FC analyses between different cortical regions of interest (ROIs) in the DAN/VAN, we extracted the fractional amplitude of low frequency fluctuations (fALFF) from each ROI as a marker of regional spontaneous neuronal activity. Although DAN regions (as opposed to the VAN regions) were largely spared from structural brain damage, they exhibited a significant reduction of inter-hemispheric FC. However, significant fMRI-behavior correlations were revealed specifically for the fALFF of one DAN-ROI in the right superior parietal lobule (SPL): the smaller the fALFF in the right posterior intraparietal sulcus, the more severe the patient's pathological attention bias and neglect-related functional impairment. In line with ‘diaschisis’, our findings confirm a crucial role of the non-lesioned but dysfunctional right SPL for the emergence of spatial neglect and its behavioral consequences. They further support targeting the SPL dysfunction by non-invasive brain stimulation in neglect rehabilitation.