A BOLD-fMRI Study On Cortical Areas Mediating Stereopsis In Comitant Strabismus

Objective:The objectives of this study are to investigate the manifestation of blood oxygen level dependent functional magnetic resonance imaging (BOLD-fMRI) in the whole brain in patients with comitant strabismus, and to explore the cortical areas mediating stereopsis and cortial activation intensity under different disparities stimulus.Methods:1. Subjects:12subjects (5female and7male, mean age16.9±3.9years) with comitant strabismus and10healthy volunteers (5female and5male, mean age21.2±2.7years) were enrolled in the study.2. Visual stimuli:The experiment was a block design, alternating between on and off stimulus phases, each taking20seconds. Three uncrossed disparity (1200",2400" and3600") random-dot stereograms (RDS) were presented during the on stimulus phase, and a black cross line fixed in the center of a white screen was displayed during the off stimulus phase.3. Data acquisition:A GE Signa HDx3.0T MRI scanner was used to acquire three dimensional whole brain anatomical images and BOLD-fMRI images.4. Image processing and data analysis:These images were processed and analyzed using the statistical parametric mapping5(SPM5) software. We used the xjView and MRIcron software to show activation regions and the whole brain BOLD fMRI images.Results:1. During all RDS stimulus, bilateral occipital lobes (BA18) showed activation in both groups. In addition, left temporal lobe (BA21) and right parietal lobe (BA2/40) showed activation in the healthy group, and right lingual gyrus (BA18) showed activation in the strabismus group. During the disparity of1200" RDS stimulus, left middle occipital gyrus (BA18) showed activation in the strabismus group, and right inferior occipital gyrus and left middle occipital gyrus (BA18) showed activation in the healthy group. During the disparity of2400" RDS stimulus, bilateral middle occipital gyruses (BA18) showed activation in the strabismus group, and bilateral middle occipital gyruses (BA18) and right inferior temporal gyrus (BA37) showed activation in the healthy group. During the disparity of3600" RDS stimulus, no significant activation area was observed in the strabismus group, and bilateral middle occipital gyruses (BA18) showed activation in the healthy group.2. The difference in cortex activation intensity between two groups was statistically significant (P<0.05). During all RDS stimuli, the significantly lower cortex activation intensity in the strabismus group was observed in left middle occipital gyrus (BA18), right inferior occipital gyrus (BA18), bialateral supramarginal gyruses (BA40), bialateral inferior temporal gyruses (BA37), bialateral inferior frontal gyruses (BA9/45) and left insular lobe (BAD). During the disparity of1200" RDS stimulus, the significantly lower cortex activation intensity in the strabismus group was mainly observed in bilateral middle occipital gyruses (BA18), bialateral inferior frontal gyruses (BA45/47), right inferior temporal gyrus (BA37), left inferior parietal lobule (BA40), left postcentral gyrus (BA2) and left insular lobe (BA13). During the disparity of2400" RDS stimulus, the significantly lower cortex activation intensity in the strabismus group was mainly observed in left middle occipital gyrus (BA18), right inferior frontal gyrus (BA18), right inferior temporal gyrus (BA37), bilateral parahippocampal gyruses (BA28) and left superior temporal gyrus (BA20); the significantly higher cortex activation intensity in the strabismus group was observed in right lingual gyrus (BA18). During the disparity of3600" RDS stimulus, the significantly lower cortex activation intensity in the strabismus group was mainly observed in right inferior frontal gyrus (BA9/47), left middle frontal gyrus (BA18), right inferior occipital gyrus (BA18) and left insular lobe (BA13); the significantly higher cortex activation intensity in the strabismus group was observed in right middle frontal gyrus (BA8/10).3. Under three different disparity stimuli, the average activation voxels in the comitant strabismus group were significantly lower than in the healthy group (P>0.05).4. The difference in cortex activation area among different disparity stimuli was not statistically significant neither in the strabismus group nor in the healthy group.Conclusions:1. Cortical activation areas in comitant strabismus patients under the RDS stimuli are smaller than healthy subjects.2. Under different disparity stimuli, cortex activation intensity and average activation voxels in comitant strabismus patients are lower than in healthy subjects.3. There is no significant change in cortex activation area in comitant strabismus patients under different disparity stimuli.4. The neural mechanism of stereopsis dysfunction in comitant strabismus patients may be associated with the decreased activation in parietal lobe and temporal lobe. Neural pathways of stereo vision may involve several encephalic regions including occipital lobe, parietal lobe, temporal lobe and frontal lobe.