Functional anatomy of predictive vergence and saccade eye movements in humans: a functional MRI investigation

Purpose: The purpose of this study is to investigate the functional neural anatomy that generates vergence eye movement responses from predictive versus random symmetrical vergence step stimuli in humans and compare it to a similar saccadic task via the blood oxygenation level dependent signal from functional MRI.

Methods: Eight healthy subjects participated in fMRI scans obtained from a 3T Siemens Allegra scanner. Subjects tracked random and predictable vergent steps and then tracked random and predictable saccadic steps each within a block design. A general linear model (GLM) was used to determine significantly (p < 0.001) active regions of interest through a combination of correlation threshold and cluster extent. A paired t-test of the GLM beta weight coefficients was computed to determine significant spatial differences between the saccade and vergence data sets.

Results: Predictive saccadic and vergent eye movements induced many common sites of significant functional cortical activity including: the dorsolateral prefrontal cortex (DLPFC), parietal eye field (PEF), cuneus, precuneus, anterior and posterior cingulate, and the cerebellum. However, differentiation in spatial location was observed within the frontal lobe for the functional activity of the saccadic and vergent network induced while studying prediction. A paired t-test of the beta weights from the individual subjects showed that peak activity induced by predictive versus random vergent eye movements was significantly (t > 2.7, p < 0.03) more anterior within the frontal eye field (FEF) and the supplementary eye field (SEF) when compared to the functional activity from predictive saccadic eye movements.

Conclusion: This research furthers our knowledge of which cortical sites facilitate a subject's ability to predict within the vergence and saccade networks. Using a predictive versus random visual task, saccadic and vergent eye movements induced activation in many shared cortical sites and also stimulated differentiation in the FEF and SEF.