Table 1.
Demographic and clinical data.
Fig 1.
HOMA-IR is the dominant predictor of overall Stop Signal Task performance in obese T2DM participants.
A) Increasing insulin resistance (HOMA-IR) predicts poorer overall performance (shorter critical stop signal delay, cSSD). B) This degradation in SST performance is a consequence of faster go speeds (shorter mGRT) with increasing insulin resistance. Models include age and metformin dose as covariates.
Fig 2.
Group contrast T-maps comparing activity between stop success (SS) and stop error (SE) trials, thresholded at punc<0.001, kE>10 voxels.
A) SS>SE reveals greater activation in SS compared with SE trials in bilateral dorsal striatum, precentral gyrus, supplementary motor and visual areas, as well as the right cingulate gyrus, temporal gyri, and right superior parietal lobule. B) SE>SS reveals greater activation for stop error trials in bilateral cingulate gyrus, medial frontal gyrus/preSMA, insula, and cerebellum.
Table 2.
Brain areas showing significant differences in activation between stop success (SS) and stop error (SE) trials.
Fig 3.
Activation in bilateral striatum predicts faster go speeds.
A) Significant association of faster go speeds (shorter mGRT) with greater activation contrast for failed vs. successful stop trials (CONSE>SS) in bilateral striatum, consistent with greater “go”-associated putamen activation in fast responders. (Striatal ROIs extracted from group SS>SE contrast map, Fig 2A). B) Whole brain voxel-wise regression of CONSE>SS against mGRT confirms a strong negative correlation in putamen bilaterally. (Map thresholded at an uncorrected p<0.005).
Fig 4.
Insulin resistance predicts brain activation in brain regions whose activities are themselves predictors of mGRT.
A) Increasing HOMA-IR predicted decreasing activation for successful vs failed stop trials (CONSS>SE) in right putamen, where lower contrast predicted faster go speeds (shorter mGRT). B) Increasing HOMA-IR predicted increasing activation for go compared with stop success trials (CONSS>GS) in right precuneus, right thalamus, left supplementary motor area, and right precentral gyrus, brain areas where greater contrast predicted faster go speeds.
Fig 5.
BMI predicts activation in right middle frontal gyrus.
Decreasing CONSS>GS activation with increasing BMI in right middle frontal gyrus, an area whose activation strength is a significant predictor of go speed (i.e. increasing activation predicted shorter mGRT, see Table B, Figure B panel A, in S1 File).
Fig 6.
Impact of insulin resistance on striatal activation mediates impulsivity in T2DM.
Through an association of increasing activation (CONSE>SS) with increasing insulin resistance (path a: HOMA-IR -> CONSE>SS), putamen activation, a predictor of faster go speeds (shorter mGRT; path b: CONSE>SS -> mGRT) mediates the faster go speeds (shorter mGRT) observed with greater insulin resistance (path c: HOMA-IR -> mGRT) observed in obese T2DM participants with a medium to large effect size (κ2 0.19, 95% CI = 0.015–0.46. Bootstrapped path coefficients a, b, c, c’ and [95% confidence intervals] determined using PROCESS in SPSS 22.