Stereoscopic visual area connectivity: a diffusion tensor imaging study

Cross-subject variability of the optic radiation anatomy in a cohort of 1065 healthy subjects

INTRODUCTION

Optic radiations are tracts of particular interest for neurosurgery, especially for temporal lobe resection, because their lesion is responsible for visual field defects. However, histological and MRI studies found a high inter-subject variability of the optic radiation anatomy, especially for their most rostral extent inside the Meyer's temporal loop. We aimed to better assess inter-subject anatomical variability of the optic radiations, in order to help to reduce the risk of postoperative visual field deficiencies.

METHODS

Using an advanced analysis pipeline relying on a whole-brain probabilistic tractography and fiber clustering, we processed the diffusion MRI data of the 1065 subjects of the HCP cohort. After registration in a common space, a cross-subject clustering on the whole cohort was performed to reconstruct the reference optic radiation bundle, from which all optic radiations were segmented on an individual scale.

RESULTS

We found a median distance between the rostral tip of the temporal pole and the rostral tip of the optic radiation of 29.2 mm (standard deviation: 2.1 mm) for the right side and 28.8 mm (standard deviation: 2.3 mm) for the left side. The difference between both hemispheres was statistically significant (p = 1.10^-8).

CONCLUSION

We demonstrated inter-individual variability of the anatomy of the optic radiations on a large-scale study, especially their rostral extension. In order to better guide neurosurgical procedures, we built a MNI-based reference atlas of the optic radiations that can be used for fast optic radiation reconstruction from any individual diffusion MRI tractography.

Effect of Impaired Stereoscopic Vision on Large-Scale Resting-State Functional Network Connectivity in Comitant Exotropia Patients

Background

Comitant exotropia (CE) is a common eye movement disorder, characterized by impaired eye movements and stereoscopic vision. CE patients reportedly exhibit changes in the central nervous system. However, it remains unclear whether large-scale brain network changes occur in CE patients.

Purpose

This study investigated the effects of exotropia and stereoscopic vision dysfunction on large-scale brain networks in CE patients via independent component analysis (ICA).

Methods

Twenty-eight CE patients (mean age, 15.80 ± 2.46 years) and 27 healthy controls (HCs; mean age, 16.00 ± 2.68 years; closely matched for age, sex, and education) underwent resting-state magnetic resonance imaging. ICA was applied to extract resting-state networks (RSNs) in both groups. Two-sample’s t-tests were conducted to investigate intranetwork functional connectivity (FC) within RSNs and interactions among RSNs between the two groups.

Results

Compared with the HC group, the CE group showed increased intranetwork FC in the bilateral postcentral gyrus of the sensorimotor network (SMN). The CE group also showed decreased intranetwork FC in the right cerebellum_8 of the cerebellum network (CER), the right superior temporal gyrus of the auditory network (AN), and the right middle occipital gyrus of the visual network (VN). Moreover, functional network connectivity (FNC) analysis showed that CER-AN, SMN-VN, SN-DMN, and DMN-VN connections were significantly altered between the two groups.

Conclusion

Comitant exotropia patients had abnormal brain networks related to the CER, SMN, AN, and VN. Our results offer important insights into the neural mechanisms of eye movements and stereoscopic vision dysfunction in CE patients.

Abnormal Low-Frequency Oscillations Reflect Abnormal Eye Movement and Stereovision in Patients With Comitant Exotropia

Background: Patients with comitant exotropia (CE) are accompanied by abnormal eye movements and stereovision. However, the neurophysiological mechanism of impaired eye movements and stereovision in patient with CE is still unclear.

Purpose: The purpose of this study is to investigate spontaneous neural activity changes in patients with CE using the amplitude of low-frequency fluctuation (ALFF) method and the machine learning method.

Materials and Methods: A total of 21 patients with CE and 21 healthy controls (HCs) underwent resting-state magnetic resonance imaging scans. The ALFF and fractional amplitude of low-frequency fluctuation (fALFF) values were chosen as classification features using a machine learning method.

Results: Compared with the HC group, patients with CE had significantly decreased ALFF values in the right angular (ANG)/middle occipital gyrus (MOG)/middle temporal gyrus (MTG) and bilateral supplementary motor area (SMA)/precentral gyrus (PreCG). Meanwhile, patients with CE showed significantly increased fALFF values in the left putamen (PUT) and decreased fALFF values in the right ANG/MOG. Moreover, patients with CE showed a decreased functional connectivity (FC) between the right ANG/MOG/MTG and the bilateral calcarine (CAL)/lingual (LING) and increased FC between the left PUT and the bilateral cerebellum 8/9 (CER 8/9). The support vector machine (SVM) classification reaches a total accuracy of 93 and 90% and the area under the curve (AUC) of 0.93 and 0.90 based on ALFF and fALFF values, respectively.

Conclusion: Our result highlights that patients with CE had abnormal brain neural activities including MOG and supplementary motor area/PreCG, which might reflect the neural mechanism of eye movements and stereovision dysfunction in patients with CE. Moreover, ALFF and fALFF could be sensitive biomarkers for distinguishing patients with CE from HCs.