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W. Bentley, L. Snyder, S. Petersen, P. Foeller, L. Tychsen; Functional MRI in Macaque Monkey With Infantile Strabismus: Nasotemporal Motion Processing and Eye Tracking. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1985.
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© ARVO (1962-2015); The Authors (2016-present)
Binocular decorrelation in the first weeks of life produces the infantile esotropia syndrome in infant primates. The animals possess all of the behavioral features observed in strabismic children, including nasotemporal asymmetries of motion processing and gaze (latent nystagmus, pursuit, OKN and ocular following). The asymmetry is evident as a bias favoring nasalward motion. The goal of the present study was to determine which gaze and motion processing brain areas are more active for nasalward motion.
A pilot functional imaging study was conducted in an anesthetized primate (age 2 yrs) who had infantile esotropia produced by 9 wks of prism goggle wear (binocular decorrelation). Anesthesia was accomplished with isoflurane (1-1.5%), and fMRI signals were recorded under conditions of dichoptic viewing using a surface coil. Blood-oxygenation level dependent (BOLD) images were obtained with 1.5 mm isotropic voxels and 2.25 mm of smoothing.
Eight trials of each of 4 conditions were tested, nasalward motion (2 conditions: right eye viewing leftward motion and left eye viewing rightward motion) vs. temporalward motion (2 conditions: right eye viewing rightward motion and left eye viewing leftward motion). A statistical map of the differential activation was derived and superimposed on a 3D reconstruction of the brain. Activation in the superior temporal sulcus in the vicinity of MT and MST was significantly stronger for nasalward compared to temporalward motion. The time course of the response was a sharp uptick in the first seconds with an overshoot followed by a long shallow downward ramp. Asymmetric activity (stronger for nasalward motion) was also apparent in VIP and FEF.
These pilot data confirm that, in infantile esotropia, gaze-related regions of the cerebral hemispheres show asymmetries in activation for nasalward vs. temporalward visual motion. More data will be required to determine whether the locations of the activation-asymmetry differ with subtype of tracking behavior and to test hypotheses regarding other cortical and subcortical areas of interest (e.g. NOT).
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