Table 1.
Characteristics of study participants.
Figure 1.
Schematic and timeline of the three trial types: Easy, Hard, and Fake Hard.
For fMRI analyses comparing error and correct responses, we did not distinguish between trial types. All trials begin with an instructional cue (300 ms) of a color (blue or yellow) indicating either a Hard or Easy trial, followed by fixation. At 1800 ms, the central fixation ring disappears (200 ms gap), and at 2000 ms, it re-appears on either the right or left side as the imperative stimulus to which participants must respond. Hard trials are distinguished by an increase in luminance of both the peripheral squares that mark the potential locations of stimulus appearance during the gap and of the imperative stimulus. Except for the Hard cue, Fake Hard trials are identical to Easy trials. In the trials depicted, the correct response is a saccade away from the stimulus on the left side of the display. An error would involve a saccade towards the stimulus. After one second, the fixation ring returns to the center, where participants return their gaze to await the next trial.
Figure 2.
Effects of MTHFR 677C>T genotype on error-related dACC activation.
Both schizophrenia patients (a) and healthy participants (b) exhibited significant condition×genotype interactions (patients: F = 4.51, p = .042; healthy participants: F = 10.32, p = .004) indicating that C/C participants, but not T allele carriers, showed significant error-related dACC activation. (c) Pseudocolor statistical maps of the relationship between 677C allele load (0, 1, or 2 copies) and error-related activation (error minus correct) in the combined group, displayed on the inflated medial cortical surface. The dACC is outlined in green. Graphs illustrate the effects of allele load on error-related activation, averaged across vertices in the anatomically defined dACC, for patients and healthy participants. Error bars indicate the standard error of the mean.
Figure 3.
Pseudocolor statistical maps of MTHFR 677C>T genotype effects in the contrast of correct antisaccades versus fixation at 4 s displayed on the left inflated medial cortical surface.
This contrast examines activation related to correctly performing an antisaccade at the time point that shows maximal activation in ocular motor regions in the combined group data. We observed robust activation in the ocular motor network, including in the cingulate eye field (which is within the dACC), that did not differ by genotype group. The dACC is outlined in green.
Figure 4.
Relation of error-related dACC activation with antisaccade error rate in C/C (a) and T carrier (b) participants.
Gray triangles indicate data points from schizophrenia patients; black circles indicate healthy participants.
Table 2.
Regions with significant (p<.05) effects of genotype on antisaccade error-related activation following whole-brain correction.