Research reportAltered functional connectivity density in high myopia
Introduction
High myopia (HM), defined as a spherical equivalent equal or less than −6 diopters, is an important public health issue. Globally, HM affects 2.9% of the world’s population [1] and its prevalence has increased over the past few decades, especially in the Asia, where HM ranges from 6.3 to 38% [2], [3], [4], [5]. Long-term HM can lead to fundus changes [6] and deficits in visual function performance [7], which has been studied extensively. However, little is known about the influence of HM on the brain neural activity.
Previous neuroimaging studies have revealed that structural and functional brain changes not only existed in neuropsychiatric diseases [8], [9], but also in diseases with long-term abnormal sensory input [10], [11], [12], [13], [14], [15]. Such as in hearing disorders [16], [17] and amblyopia [15], [18], gray matter reductions were reported. Further studies on amblyopia also detected abnormal functional connectivity (FC) between visual cortex and high-level regions, which indicates a noteworthy impact of abnormal visual experience on the neural activity of the brain [19], [20]. Although with a corrected visual acuity, functional performances of myopic eye, such as contrast sensitivity [21], resolution acuity [22], and even visual attention [23], [24], are abnormal in contrast to emmetropics. Thus, it can be inferred that long period of myopic vision may result in changes of brain neural activity in HM as well. Actually, our previous study has shown white matter changes in HM, which occurred not only in visual regions but also in some parietal and frontal areas [25]. Nevertheless, there is not any neuroimaging study about the functional changes in the brain of HM.
Functional connectivity density (FCD) mapping [26], [27] is a voxelwise data-driven method which can measure the amount of functional connections between brain regions and it allows the identification of hub regions that play important roles in information processing [26]. Based on the hub regions, FC analysis can be further performed to get insight into the functional organization of the brain. Thus, in this study FCD mapping was used to identify regions with FCD changes in HM and seed-based correlation analysis was performed on those regions to investigate FC changes for further network analysis. Moreover, gray matter volume was also investigated based on the regions showing FCD alterations.
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Subjects
Fifty-nine right-handed students from Tianjin Medical University were recruited for this study and 27 of them were HM (5 males/22 females; range = 21–25 years) with a spherical equivalent ≤ −6.00 diopters. The remaining 32 were emmetropics taken as normal controls (NC, 14 males/18 females; range = 18–25 years). There was no significant difference in age (HM: 23.22 ± 1.34 years versus NC: 22.75 ± 1.72 years; two-sample two tailed t-test, t = 1.16, P = 0.25) or education level (HM: 16.11 ± 1.37 years versus NC:
Spatial distribution of FCD
The resting-state FCD maps of each subject were calculated and similar spatial patterns were observed in the HM and NC groups in the averaged resting-state FCD maps. Short-range FCD was higher in the cingulate cortex, precuneus (preCun), cuneus/lingual/calcarine regions, parietal lobe and prefrontal cortex. Long-range FCD was higher in the cingulate cortex, preCun, cuneus/lingual/calcarine regions, inferior parietal lobule and middle/dorsolateral prefrontal cortex (Fig. 1).
Between-group differences in FCD
Between-group
Discussion
In this study, FCD mapping and FC analysis were combined to investigate cortical FC changes in the HM. Compared to the NC, short- and long-range FCD in the PCC/preCun were both decreased in the HM, as well as reduced long-range FCD in the left ITG, right SMG and right rlPFC. The uncorrected visual acuity was positively correlated with the long-range FCD in the rlPFC in HM group. In particular, compared with the NC, the HM showed significantly decreased FC not only between SMG and rlPFC
Conflict of interest
The authors declare no conflict of interest.
Acknowledgment
The study was supported by the Applied Basic Research Programs of Science and Technology Commission Foundation of Tianjin, People’s Republic of China (Grant no. 10 JCYBJC10700).
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