Abstract
Objective: Non-invasive brain stimulation (NIBS) is already known to improve visual field functions in patients with optic nerve damage and partially restores the organization of brain functional connectivity networks (FCNs). However, because little is known if NIBS is effective also following brain damage, we now studied the correlation between visual field recovery and FCN reorganization in patients with stroke of the central visual pathway.Method: In a controlled, exploratory trial, 24 patients with hemianopia were randomly assigned to one of three brain stimulation groups: transcranial direct current stimulation (tDCS)/transcranial alternating current stimulation (tACS) (ACDC); sham tDCS/tACS (AC); sham tDCS/sham tACS (Sham), which were compared to age-matched controls (n = 24). Resting-state electroencephalogram (EEG) was collected at baseline, after 10 days stimulation and at 2 months follow-up. EEG recordings were analyzed for FCN measures using graph theory parameters, and FCN small worldness of the network and long pairwise coherence parameter alterations were then correlated with visual field performance.Result: ACDC enhanced alpha-band FCN strength in the superior occipital lobe of the lesioned hemisphere at follow-up. A negative correlation (r = −0.80) was found between the intact visual field size and characteristic path length (CPL) after ACDC with a trend of decreased alpha-band centrality of the intact middle occipital cortex. ACDC also significantly decreased delta band coherence between the lesion and the intact occipital lobe, and coherence was enhanced between occipital and temporal lobe of the intact hemisphere in the low beta band. Responders showed significantly higher strength in the low alpha band at follow-up in the intact lingual and calcarine cortex and in the superior occipital region of the lesioned hemisphere.Conclusion: While ACDC decreases delta band coherence between intact and damaged occipital brain areas indicating inhibition of low-frequency neural oscillations, ACDC increases FCN connectivity between the occipital and temporal lobe in the intact hemisphere. When taken together with the lower global clustering coefficient in responders, these findings suggest that FCN reorganization (here induced by NIBS) is adaptive in stroke. It leads to greater efficiency of neural processing, where the FCN requires fewer connections for visual processing.
Highlights
The potential to restore visual fields following central visual system damage has attracted some attention during the last few decades [1,2,3,4,5,6,7,8]
We found no significant correlation of lesion age with functional connectivity network (FCN) pre–post difference of the two most important parameters (“strength” and “centrality”) on the alpha band, showing that lesion age had no impact on our FCN parameters
The other two groups’ median FOV remained unchanged after treatment and at follow-up. This suggests that visual functionality of the ACDC group had a trend of an enhancement at a group level compared with baseline, which was not observed in the other two groups
Summary
The potential to restore visual fields following central visual system damage has attracted some attention during the last few decades [1,2,3,4,5,6,7,8]. For example, leads to homonymous hemianopia whereby a quarter or half of the visual field in both eyes is lost following damage [9] This impairs visual functional abilities and quality of life [10], increasing the risk to fall or having difficulties in reading, with secondary deficits such as depression and social isolation [10,11,12,13,14]. While visual training can improve visual fields well after the initial spontaneous recovery phase [2, 3, 15], additional recovery of vision can take many months of daily exercises To overcome this limitation, efforts were made to use non-invasive brain stimulation (NIBS) as a new therapeutic approach. NIBS can be used to purposely modulate neuron’s excitation and inhibition in many neurological diseases with a potential to induce recovery of function [29]
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