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. 2020 Aug 3;20(8):17.
doi: 10.1167/jov.20.8.17.

Test-retest of a phoria adaptation stimulus-induced functional MRI experiment

Cristian Morales  1 , Suril Gohel  2 , Mitchell Scheiman  3 , Xiaobo Li  1 , Elio M Santos  1 , Ayushi Sangoi  1 , Tara L Alvarez  1
Affiliations

Test-retest of a phoria adaptation stimulus-induced functional MRI experiment

Cristian Morales et al. J Vis. .

Abstract

This study was designed to identify the neural substrates activated during a phoria adaptation task using functional magnetic resonance imaging (MRI) in young adults with normal binocular vision and to test the repeatability of the fMRI measurements for this protocol. The phoria adaptation task consisted of a block protocol of 90 seconds of near visual crossed fixation followed by 90 seconds of far visual uncrossed fixation, repeated three times; the data were collected during two different experimental sessions. Results showed that the oculomotor vermis, cuneus, and primary visual cortex had the greatest functional activity within the regions of interest studied when stimulated by the phoria adaptation task. The oculomotor vermis functional activity had an intraclass correlation coefficient (ICC) of 0.3, whereas the bilateral cuneus and primary visual cortex had good ICC results of greater than 0.6. These results suggest that the sustained visual fixation task described within this study reliably activates the neural substrates of phoria adaptation. This protocol establishes a methodology that can be used in future longitudinal studies investigating therapeutic interventions that may modify phoria adaptation.

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Figures

Figure 1.
Figure 1.
(A) Experimental setup within the MRI scanner room. The participant lies on the gantry within the bore of the magnet and observes the screen through a mirror placed along the top of the head coil. (B) Timing sequence of the phoria adaptation task. The stimuli began with a near crossed sustained convergence visual stimulus for 90 seconds followed by a far uncrossed sustained visual stimulus for 90 seconds, a process that was repeated three times for a total of 540 seconds. (C) Visual stimulus presentation for the near crossed and far uncrossed sustained fixation task. (D) Visual stimulus timing sequence that alternates between near crossed and far uncrossed visual sustained fixation.
Figure 2.
Figure 2.
Group-level behavioral phoria adaptation experiment using a 6 base-in prism (A) and 6 base-out prism (B) showing the mean ± SD (STDEV) of all participants. The exponential fit of the group is plotted in solid and the dashed line shows the amount of phoria adaptation after 90 seconds, which was the time used within the scanner for sustained fixation.
Figure 3.
Figure 3.
(A) Activation maps for visit 1, and (B) activation maps for visit 2. Oculomotor vermis, V1, and cuneus are significantly active areas. (C) ICC map thresholded at ICC > 0.4, which is fair or better reliability. (D) Spatial extent overlap between visits with selected ROIs. The legend shows the 5-mm sphere for each of the following ROIs: frontal eye fields (FEF) in pink, parietal eye fields (PEF) in purple, vermis in red, cuneus in green, supplemental eye field (SEF) in magenta, and primary visual cortex (V1) in yellow. Slices are designated as I (inferior) or S (superior).
Figure 4.
Figure 4.
Bar-and-whisker plot for the mean beta weight (4A) and peak beta weight (4B) for the designated ROIs from visit 1 (blue) and visit 2 (red).
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