V11. Functional hierarchy within an overall network for visual motion processing and ocular-motor control at rest

Abstract

Introduction Visual motion processing on one hand and ocular motor functions on the other are rarely studied together in vivo in humans. The interrelation of these functional networks is rather unclear, even though their functional dependence seems obvious. In several fMRI studies the essential nodes of both networks could be localized using voluntary optokinetic ('look') nystagmus (OKN) in the horizontal plane incorporating visual motion tracking (Dieterich et al., 2009). Here, functional connectivity (FC) between these nodes representing both networks was studies using resting-state FC. Methods Resting-state fMRI data of 200 healthy adults (age 44.1±17.9; 79 male) were included in the cross correlation analysis of 9 bilateral nodes including frontal (FEF), supplementary (SEF), cingulate (CEF) and parietal eye fields (PEF), V5 and V6, as well as the superior colliculus (SupCol), the lateral geniculate body (CGL) and the globus pallidus (GlobPal). The necessary ROIs were obtained in a separate OKN fmri experiment with 21 healthy subjects. After spatial preprocessing and confound removal using 24 motion regression and mean signal within white matter and cerebral spinal fluid and band-pass filtering (0.01–0.08Hz), each ROI was represented by the first eigenvariate of the respective voxels' time-series. For each node pair partial correlations were computed within subjects and Fisher Z transformed for one group t -tests corrected for the influence of age and gender resulting in an 18×18 cross correlation matrix. Subsequently, hierarchical cluster analysis was applied to analyze sub-clustering within the overall network. Results The analysis showed consistent FC between each regions respective homotopical partner. Hierarchical clustering revealed an overall split between one cluster comprising SEF, FEF, CEF and GlobPal and a second including CGL, SubCol, V6 as well as PEF and V5. Conclusion This new approach revealed an observer- and task-indepedent separation of the cortical eye fields into two main groups either responsible for voluntary ocular motor control (SEF, FEF, CEF, and GlobPal) or involved in visual motion target tracking streams (CGL, SupCol, PEF, V5, and V6). The further subgrouping of PEF and V5 together with area V6 representing an isolated cluster within the second group seem to reflect their order and importance along the dorsal visual stream known from lesion studies (Pierrot-Deseilligny et al., 2004). The other subgroup of CGL and SupCol may represent the early nodes of the network involved in voluntary and reflexive ocular motor control. In sum, these neuroscientifically sound network findings for visual motion and ocular motor control derived from task-free data give a promising outlook for the novel concept of hierarchical clustering (Figs. 1 and 2).