How right dorsomedial lesions lead to neglect: A functional network-level framework.

Spatial neglect-a disorder characterized by impaired exploration of contralesional space-has only recently been reported following lesions to dorsomedial regions of the right hemisphere. Consequently, the mechanisms underlying the occurrence of neglect in this context remain largely unexplored. Here, we investigated whether alterations in functional connectivity could account for this phenomenon by longitudinally assessing resting-state fMRI in a patient before and after tumor resection. A 71-year-old male underwent resection of an oligodendroglioma involving the right superior frontal gyrus and cingulum. Neuropsychological assessment and resting-state fMRI were acquired before and after surgery. Peripersonal and personal neglect were assessed with two different cancellation tests and the Comb and Razor Test (CRT). System Segregation (SyS), i.e., the balance of within and between network functional connectivity, was computed at both whole-brain and network-specific levels and compared with 20 age-matched healthy controls using Crawford's modified t-test. While no sign of neglect was observed preoperatively, the patient exhibited both peripersonal and personal neglect after surgery. Compared to controls, postoperative data revealed a significant reduction in whole-brain SyS (p < .001). At the network level, the ventral attention network (VAN) showed preserved segregation preoperatively but a marked postoperative decrease (p < .001). These findings show, for the first time, that the clinical manifestation of neglect after right dorsomedial regions may be explained by lesion-induced alterations in large-scale functional connectivity. In particular, reduced VAN segregation may reflect impaired functional differentiation underlying deficits in spatial attention, thereby shedding light on the mechanisms underlying dorsomedial lesions neglect presentation.