Figure 1.
Experimental set-up and design.
The schematic of the custom fMRI compatible light emitting diodes (LEDs) for the saccade (image A1) and vergence (image A2) experiments. Subjects would sustain fixation (plot B1) on either the midline target during the saccade experiment or near target during the vergence experiment for 20 seconds and then track the illuminated LEDs in a random pattern for 20 seconds (plot B2). A block design protocol is used where the “off’ stimulus is sustained fixation and the “on” stimulus is the random eye movement tracking.
Figure 2.
Typical reference vectors from one subject (S4) from the saccadic data set (upper plot) and the vergence data set (lower plot).
The source signals have a high Pearson correlation coefficient with the experimental block design (r = 0.67 for the saccade experiment and r = 0.77 for the vergence experiment).
Figure 3.
Experimental block design of 3.5 cycles alternating between fixation and eye movements (Plot A).
Fixation and saccadic eye movements to targets 10 degrees into the left or right visual field or along midline plotted as position (deg) as a function of time (sec) (Plot B). Functional activity within FEF during saccadic stimulation plotted as percent signal change from baseline as a function of time (sec) (Plot C). Fixation and vergence eye movements to targets 2, 3, or 4 degrees along midline plotted as position (deg) as a function of time (sec) (Plot D). Functional activity within FEF during vergence stimulation plotted as percent signal change from baseline as a function of time (sec) (Plot E).
Figure 4.
Functional activation for the group analysis of fixation versus random eye movements for the saccade (left side) and the vergence data set (right side) showing typical commonality.
DLPFC = dorsolateral prefrontal cortex and BA = Brodmann Area. The number of mm above the bicommissural plane is indicated. The functional activation is denoted by the scale bar as a z-score from a minimum of 2.0 to a maximum value of 6.6. Data are overlaid onto a standardized Talairach-Tournoux normalized image. Semi-inflated images of the functional activity within the lateral hemispheric surface and cerebellum are displayed using Caret software.
Figure 5.
Axial images showing differentiation between the functional activity of the frontal eye fields (FEF) from saccade (left) and vergence (right) eye movements.
Functional activity using the GLM analysis is shown in Figure 5A. The voxel wise positive and negative paired t-tests show significant differentiation between FEF for vergence and saccades, Figure 5B. The GLM analysis reports activity using the scale bar of a z-score from 2.0 to 6.6. The paired t-tests using the beta weights from the GLM analysis reports significant differences from T = ±2.3 to ±11 (two-tailed p-value = 0.05 to p<0.0001). Functional activity and paired t-test significant differences are overlaid onto Talairach-Tournoux normalized axial structural images. The axial slice is 49 mm superior to the bicommissural plane for all images. L: left; R: right. The superior frontal sulcus is denoted with blue arrows and the precentral sulcus is denoted with green arrows in Figure 5A. The significant differences within FEF are denoted with red arrows for vergence (FEFv) and yellow arrows for saccades (FEFs) in Figure 5B.
Table 1.
Average peak activation of the fixation versus random saccadic oculomotor task in Talairach-Tournoux coordinates with the level of significance denoted as a z-score.
Table 2.
Average peak activation of the fixation versus random vergence oculomotor task in Talairach-Tournoux coordinates with the level of significance denoted as a z-score.
Figure 6.
Percent signal change from baseline within the posterior (left) and anterior (right) portions of the frontal eye fields (FEF).
Significantly more signal change is observed within the posterior portion of FEF in the saccade compared to the vergence data set. Significantly more signal changes is observed within the anterior portion of FEF in the vergence compared to the saccade data set.
Table 3.
Individual subject analysis of saccade and vergence FEF.
Figure 7.
Functional activity within the midbrain using a GLM analysis (Plot A).
Positive and negative paired t-test statistical spatial map showing differentiation between the midbrain for the fixation versus random saccadic and vergence tasks identified via the cross hair. A positive T value is for the saccade minus vergence data set and a negative T value is for the vergence minus saccade data set (Plot B). Typical time series signal from the midbrain which has a correlation of 0.5 with the block design (square wave) (Plot C). Talairach Tournoux coordinates are: 7 R, 19 P and 15 I. Comparison of the percent signal change from baseline of the same time series signals from the saccade and vergence data sets within the midbrain (Plot D).
Table 4.
Individual subject analysis of the midbrain from the vergence data set.
Table 5.
Saccade minus vergence data sets / positive paired t-test and vergence minus saccade data sets / negative paired t-test statistics showing differentiation between FEF and midbrain in comparing fixation versus random saccade and vergence tasks.