Functional interactions in patients with hemianopia: A graph theory-based connectivity study of resting fMRI signal

Abstract

The assessment of task-independent functional connectivity (FC) after a lesion causing hemianopia remains an uncovered topic and represents a crucial point to better understand the neural basis of blindsight (i.e. unconscious visually triggered behavior) and visual awareness. In this light, we evaluated functional connectivity (FC) in 10 hemianopic patients and 10 healthy controls in a resting state paradigm. The main aim of this study is twofold: first of all we focused on the description and assessment of density and intensity of functional connectivity and network topology with and without a lesion affecting the visual pathway, and then we extracted and statistically compared network metrics, focusing on functional segregation, integration and specialization. Moreover, a study of 3-cycle triangles with prominent connectivity was conducted to analyze functional segregation calculated as the area of each triangle created connecting three neighboring nodes. To achieve these purposes we applied a graph theory-based approach, starting from Pearson correlation coefficients extracted from pairs of regions of interest. In these analyses we focused on the FC extracted by the whole brain as well as by four resting state networks: The Visual (VN), Salience (SN), Attention (AN) and Default Mode Network (DMN), to assess brain functional reorganization following the injury. The results showed a general decrease in density and intensity of functional connections, that leads to a less compact structure characterized by decrease in functional integration, segregation and in the number of interconnected hubs in both the Visual Network and the whole brain, despite an increase in long-range inter-modules connections (occipito-frontal connections). Indeed, the VN was the most affected network, characterized by a decrease in intra-and inter-network connections and by a less compact topology, with less interconnected nodes. Surprisingly, we observed a higher functional integration in the DMN and in the AN regardless of the lesion extent, that may indicate a functional reorganization of the brain following the injury, trying to compensate for the general reduced connectivity. Finally we observed an increase in functional specialization (lower between-network

Efficacy of Tai Chi on lower limb function of Parkinson’s disease patients: A systematic review and meta-analysis

“…Previous studies found that PD patients with freezing of gait showed reduced network connectivity in the visual network (VN; Rogge et al, 2018 ; Ruan et al, 2020 ). The VN is composed of bilateral striate and extrastriata visual Areas ( Pedersini et al, 2020 ). Visual proprioceptive conflict may affect gait and balance, and visual cues can improve balance and prevent falls in patients with PD ( Assländer et al, 2015 ).…”

Mechanisms of Motor Symptom Improvement by Long-Term Tai Chi Training in Parkinson's Disease Patients

“…Our results indicated association between enhanced VN function and improved BBS scores. The VN was composed by bilateral striate and extrastriate visual areas [25]. Visual-proprioceptive sensory con ict could in uence gait and balance [26].…”

“…We also observed change of DMN was related to improvement in UPDRS and UPDRS-III. The DMN included the hippocampus, parahippocampal, fusiform and angular gyrus, the precuneus and the middle temporal gyrus [25]. Precuneus is one of the functional hub regions of DMN, and its interactions with sensorimotor network were positively associated with motor performances [29].…”

Resting-State Functional Magnetic Resonance Imaging and Functional Connectivity Density Mapping in Patients With Optic Neuritis

“…The current study investigated the alterations of functional organization for ON patients using a recently developed FCD method. FCD, a reliable rs-fMRI analytical method has been widely used in the study of various ophthalmic and neurological diseases ( Wang et al, 2014 ; Qin et al, 2015 ; Zhai et al, 2016 ; Hu et al, 2017 ; Chen et al, 2019 ; Li et al, 2019 ; Dai et al, 2020 ; Pedersini et al, 2020 ; Table 4 ). In addition to impaired visual function, the ON group showed significantly reduced longFCD values compared with HCs in the left IFGtriang, right PCUN, right ACG/DCG, and left DCG/SMA ( Figure 3 ).…”