Evidence for cerebellar motor functional reorganization in brain tumor patients: An fMRI study

Distributed changes of the functional connectome in patients with glioblastoma

Glioblastoma might have widespread effects on the neural organization and cognitive function, and even focal lesions may be associated with distributed functional alterations. However, functional changes do not necessarily follow obvious anatomical patterns and the current understanding of this interrelation is limited. In this study, we used resting-state functional magnetic resonance imaging to evaluate changes in global functional connectivity patterns in 15 patients with glioblastoma. For six patients we followed longitudinal trajectories of their functional connectome and structural tumour evolution using bi-monthly follow-up scans throughout treatment and disease progression. In all patients, unilateral tumour lesions were associated with inter-hemispherically symmetric network alterations, and functional proximity of tumour location was stronger linked to distributed network deterioration than anatomical distance. In the longitudinal subcohort of six patients, we observed patterns of network alterations with initial transient deterioration followed by recovery at first follow-up, and local network deterioration to precede structural tumour recurrence by two months. In summary, the impact of focal glioblastoma lesions on the functional connectome is global and linked to functional proximity rather than anatomical distance to tumour regions. Our findings further suggest a relevance for functional network trajectories as a possible means supporting early detection of tumour recurrence.

Paradoxical Activation in the Cerebellum During Language fMRI in Patients with Brain Tumors: Possible Explanations Based on Neurovascular Uncoupling and Functional Reorganization

The cerebellum is known for its crossed activation pattern with the contralateral cerebral hemisphere during language functional magnetic resonance imaging (fMRI) tasks in healthy patients. Crossed cerebro-cerebellar activation has been previously shown to occur in patients with brain tumors not affecting the activation areas. However, the presence of a tumor in left Broca's area in the inferior frontal gyrus is known to disrupt cerebral activation during language tasks. This study investigated if crossed cerebro-cerebellar activation patterns for language tasks would still occur in such patients. A total of 43 right-handed patients with a glioma affecting left Broca's area were examined for their cerebral and cerebellar activation during an fMRI language task. Only 13 of the 43 patients exhibited crossed cerebro-cerebellar activation patterns. Statistically significant differences of atypical cerebro-cerebellar activation patterns were found between cerebral right-dominant (RD) and cerebral co-dominant (CD) (p < 0.001) as well as cerebral RD and cerebral left-dominant (LD) patients (p < 0.01), while no differences were found when patients were divided based on cerebellar dominance (p > 0.75) or tumor grade (p > 0.5). No relation was found between the cerebellar and cerebral laterality index (LI) values (ρ = - 0.20; p = 0.21). Atypical activation patterns are suspected to have been caused by the tumor, perhaps a result of contralateral reorganization in some cases and false negative activation in left Broca's area from neurovascular uncoupling (NVU) in others. Cerebellar activation may also potentially indicate cerebral false negative behavior and future cerebral contralateral reorganization.

Characterization of Hand Clenching in Human Sensorimotor Cortex Using High-, and Ultra-High Frequency Band Modulations of Electrocorticogram

Functional mapping of eloquent cortex before the resection of a tumor is a critical procedure for optimizing survival and quality of life. In order to locate the hand area of the motor cortex in two patients with low-grade gliomas (LGG), we recorded electrocorticogram (ECoG) from a 113 channel hybrid high-density grid (64 large contacts with diameter of 2.7 mm and 49 small contacts with diameter of 1 mm) while they executed hand clenching movements. We investigated the spatio-spectral characteristics of the neural oscillatory activity and observed that, in both patients, the hand movements were consistently associated with a wide spread power decrease in the low frequency band (LFB: 8–32 Hz) and a more localized power increase in the high frequency band (HFB: 60–280 Hz) within the sensorimotor region. Importantly, we observed significant power increase in the ultra-high frequency band (UFB: 300–800 Hz) during hand movements of both patients within a restricted cortical region close to the central sulcus, and the motor cortical “hand knob.” Among all frequency bands we studied, the UFB modulations were closest to the central sulcus and direct cortical stimulation (DCS) positive site. Both HFB and UFB modulations exhibited different timing characteristics at different locations. Power increase in HFB and UFB starting before movement onset was observed mostly at the anterior part of the activated cortical region. In addition, the spatial patterns in HFB and UFB indicated a probable postcentral shift of the hand motor function in one of the patients. We also compared the task related subband modulations captured by the small and large contacts in our hybrid grid. We did not find any significant difference in terms of band power changes. This study shows initial evidence that event-driven neural oscillatory activity recorded from ECoG can reach up to 800 Hz. The spatial distribution of UFB oscillations was found to be more focalized and closer to the central sulcus compared to LFB and HFB. More studies are needed to characterize further the functional significance of UFB relative to LFB and HFB.