Prefrontal Cortex Oxygenation Evoked by Convergence Load Under Conflicting Stimulus-to-Accommodation and Stimulus-to-Vergence Eye-Movements Measured by NIRS

Figures

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  FIGURE 1. Visualization of stimulus to convergence during conflicting stimulus-to-accommodation and stimulus-to-vergence eye-movements. Participants fixated upon the bar presented separately to the left and right eyes through polarized filters. A computer setup was used that enabled horizontal vergence load to be induced dynamically. When convergence eye movements were stimulated, a conflicting stimulation to accommodation and vergence was induced since accommodation needs to be maintained at 1.54 diopters (i.e., the distance to the bar stimuli projected on the screen, illustrated by the grey stimulus bar) to see the bar clearly, and not to the corresponding distance of the vergence angle of the eyes (illustrated by the black bars). By increasing the horizontal distance between the two images (black bars), convergence was stimulated and by reducing the horizontal distance, divergence was stimulated. If subjects did not comply with the vergence stimulus change by producing compensatory divergence/vergence eye movements, then diplopia resulted.

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  FIGURE 2. Plots of stimuli (D) to convergence during conflicting stimulus-to-accommodation and stimulus-to-vergence eye-movements presented to the subjects during the two 10-min visual conditions Conv and Cc. The individual magnitude of stimulation to convergence eye-movements shown herein constitute 80% of the mean threshold value for diplopia (convergence break point). Figure only shows one cycle of horizontal oscillations in added convergence load relative to the starting stimulus distance 1.65 diopters (stippled reference line).

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  FIGURE 3. Typical NIRS time series plot of individual changes in HbO2, HHb, and tHb during the 2-min baseline condition (to the left of the stippled vertical line), and during the 10-min visual Ctrl condition (to the right of the stippled vertical line).

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  FIGURE 4. Temporal pattern of changes in the concentration of oxygenated hemoglobin (ΔHbO2) and deoxygenated hemoglobin (ΔHHb) along with variations in total hemoglobin (ΔtHb) in dlPFC across visual conditions (figure shows mean values, and standard errors). (A) Control condition Ctrl. (B) Convergence load condition Conv. (C) Cognitive control condition Cog. (D) Combined Convergence and Cognitive load, condition Cc. The stippled horizontal reference line denotes no change in baseline subtracted hemodynamic activity.

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  FIGURE 5. Temporal pattern of changes in the concentration of oxygenated hemoglobin (ΔHbO2) and deoxygenated hemoglobin (ΔHHb) along with variations in total hemoglobin (ΔtHb) in dlPFC across visual conditions for each participant in the low and high convergence load subgroup (figure shows mean values and standard errors). (A) Control condition Ctrl. (B) Convergence load condition Conv. (C) Cognitive control condition Cog. (D) Combined convergence and cognitive load, condition Cc. The stippled horizontal reference line denotes no change in baseline subtracted changes.