Effective connectivity in cortical networks underlying visual motion processing and ocular-motor control
Creators: name: Eulenburg, Peter Zu
name: Bauermann, Thomas
name: Eickhoff, Simon B.
Publisher: name: F1000Research
Year: 2016

description: Introduction: Human ocular motor functions and visual motion processing have mostly been studied in segregated networks based on recordings in non-human primates and conventional fMRI studies. Voluntary optokinetic ("look") nystagmus (OKN) in the horizontal plane, however, contains all essential forms of eye movements whilst at the same time representing a visual motion-tracking task.<sup>1</sup> With it one can activate all known eye fields in humans and obtain precise regions of interest for the respective areas. Aim of the presented approach was to derive an integrative and wholesome network sequence from resting state data for ocular motor and visual motion networks in a large sample of healthy adults by means of ROI analysis.<br> <br>Methods: The differential effects of a horizontal optokinetic stimulation versus a flashing visual control stimulus were studied in 20 right-handed healthy volunteers in a 3 T scanner with a 32-channel head coil. The time course for eight regional responses were extracted for all subjects through a general linear model analysis (p &lt;0.05 FDR corrected at cluster level) after standard SPM preprocessing. Hence we estimated 3888 different, albeit anatomically suitable models for each subject in SPM8 with the DCM 10 framework and performed a random as well as a fixed effects bayesian model selection (BMS) to identify the most likely generative model of our data.<br> <br>Results: Model evidence in fixed and random BMS converged on the same core network featuring a bidirectional connectivity of the frontal (FEF) and parietal eye fields (PEF). The network contained a signal loop through a backward connection of the frontal eye fields towards MT/V5. BMS also showed that all driving inputs entered our network from subcortical structures in the respective primary visual cortex V1 and not directly  into MT/V5 or even the frontal eye fields. Direct input from V1 was only observed for MT/V5 and the frontal eye fields. The direction of horizontal OKN was reflected in a significant modulation of the forward connection from MT/V5 and the FEF respectively towards the parietal eye fields within each hemisphere. Hemispheric crosstalk (i.e., transcallosal connectivity) between the paired regions (V1, MT/V5, PEF or FEF) was not found to be of relevance within the context of our model.<br><br>Conclusions: Our study shows that a unifying cerebral network for visual motion and ocular motor processing can be modelled from fMRI data by means of DCM. The model with the highest posterior indicated a looped convergence of ocular motor and motion information in MT/V5 and the parietal eye fields within the context of our task. In accordance with lesion studies<sup>2</sup> neither the frontal nor the parietal eye fields but soley the primary visual cortex was found to be the main cortical gateway for all relevant downstream processing.<br><br>References:<br>1) Konen, C. S., Kleiser, R., Seitz, R. J. &amp; Bremmer, F. An fMRI study of optokinetic nystagmus and smooth-pursuit eye movements in humans. <i>Exp Brain Res</i> 165, 203-216 (2005).<br><br>2) Giaschi, D.<i> et al.</i> Conscious visual abilities in a patient with early bilateral occipital damage. <i>Developmental medicine and child neurology</i> 45, 772-781 (2003).<br>