Eye movement is controlled by a widespread network of cortical and subcortical areas, the oculomotor brain network, thus accurate measurement of these movements could represent a non-invasive method to reflect (dys)functioning of these interconnected areas. This is especially relevant for diseases in which network disruption is known to represent a key pathological feature, as in multiple sclerosis (MS).
To investigate the association between saccadic eye movements and functional connectivity of the oculomotor brain network in patients with MS.
Subjects were included from the prospective Amsterdam MS cohort. A validated standardized infrared oculography protocol (DEMoNS) was used for quantifying pro-saccades and anti-saccades (reflexive and voluntary saccadic eye movements, respectively). After resting-state magnetoencephalography (MEG) measurement, data pre-processing and beamforming of the MEG data to source space, 73 oculomotor regions of the Brainnetome atlas were included based on previous literature (i.e. the FOcuS atlas). The phase lag index (PLI) was used as a measure of functional connectivity (FC) between all regions within the oculomotor network (and it’s subnetworks) for the six conventional frequency bands. The relationship between saccadic parameters and mean FC was analyzed using multivariate linear regression models adjusted for sex, age and disease type. Effect size modification by sex was additionally investigated.
The 183 included patients with MS showed altered saccadic eye movements compared to the 58 included healthy controls. Regarding pro-saccades, worse saccadic eye movement performance was mainly related to a higher FC in theta and gamma bands and a lower connectivity in alpha and beta bands. Strongest relations with FC were found for peak velocity and the parietal eye field (theta band, β -2.1 E-4, p=0.006), gain and the precuneus (gamma band, β -1.3 E-4, p=0.003) and gain and the inferior frontal eye field (theta band, β -21.0 E-4, p<0.001). For anti-saccades, the strongest associations were found between the proportion of errors and the thalamus (beta band, β 8.0 E-4, p=0.006) and error of the final eye position and the precuneus (theta band, β -6.2 E-4, p=0.004). For female MS patients the proportion of errors was also strongly related to the supplementary eye field (gamma band, β 6.4 E-4, p=0.003) and for male patients the latency of a correct response to the cingulate eye field (delta band, β 5.3 E-4, p=0.006).
Saccadic eye movements were related to altered functional connectivity of fronto-parietal brain regions and the thalamus in patients with MS. Furthermore, there was evidence for a relevant sex difference in patterns of functional damage of the oculomotor brain network. This network approach provides an additional backing for the future use of eye movement measurement as an easy applicable tool for monitoring or predicting the disease MS.