Objectives: This study investigates how ON affects the functional connectivity of brain regions with primary visual cortex (V1).
Methods: Twenty patients (mean age = 34; 2 males) with unilateral ON as a clinically isolated syndrome (CIS) or associated with MS and 12 healthy controls underwent 3 imaging sessions at symptom onset (baseline), 6-months and 12-months post-ON. Image acquisition was conducted using a 3T MR scanner and consisted of anatomical images for co-registration of fMRI data; task-related fMRI scan to localize primary visual cortex (V1); and two 5-min resting-state fMRI scans (Eyes Open & Eyes Closed).
Results: For eyes open and eyes closed at baseline, controls have stronger functional connections between V1 and areas involved in processing vision (secondary and associative visual cortex, precuneus, superior parietal lobule), touch (somatosensory association cortex), movement (premotor cortex), sound (primary auditory cortex) and awareness (dorsal posterior cingulate cortex) than ON patients. Patients show increased functional connectivity between V1 and both frontal and anterior temporal cortices 12 months post-ON for the eyes open condition. For both eyes open and eyes closed, MS patients show a unique pattern of functional connectivity as compared with CIS patients. Both controls and MS patients show an increase in functional connectivity between premotor, dorsolateral prefrontal, posterior cingulate cortices and V1 compared to CIS patients. In contrast, both controls and CIS patients show an increase in functional connectivity between anterior prefrontal, anterior cingulate, secondary visual areas and V1 as compared to MS patients.
Conclusions: Functional connections between V1 and other brain areas are altered in the presence of ON, specifically in areas involved with complex visual processing. An increase in functional connectivity at 12 months after recovery from ON suggests compensatory mechanisms or cortical plasticity may be involved. ON patients with MS can be distinguished from CIS patients by comparing the resting-state functional connectivity between V1 and secondary visual areas.