Figure 1.
Classical conditioning fMRI paradigm.
One of two neutral stimuli (Cue A or Cue B) was followed by an outcome stimulus (reward or non-reward) after a 6-second delay. Cue A was followed by the delivery of the reward 66% of the time and non-reward 33% of the time. Cue B was always followed by non-reward. Participants were told they would receive the equivalent of R$3 for each reward outcome. The length of the inter-trial delay was varied.
Figure 2.
Striatal responses to reward anticipation and reward delivery in the ADHD and control groups.
Brain activation displays were generated by overlaying SPM t-maps resulting from the group-level analyses on an MNI standard brain (p<.005 uncorrected, cluster size ≥5 voxel, for visualization purposes) and applying a gray matter mask. (A) Increased activation in the left dorsal striatum (head of caudate) and right ventral striatum (nucleus accumbens and ventral putamen) during reward anticipation in the control group. (B) Increased activation in the left dorsal striatum (head of caudate), left ventral striatum (ventral regions of the head of caudate), and right ventral striatum (nucleus accumbens and ventral putamen) in response to reward delivery in ADHD. (C) Bar graphs represent mean parameter estimates and standard errors from the GLM analyses examining the effects of reward anticipation (Cue A delay – Cue B delay contrast) and reward delivery (Cue A reward – Cue B non-reward contrast), which were extracted from the local maxima observed within the a priori-defined ROIs based on a meta-analysis (Liu et al., 2011); MNI x, y, z = 18, 17, −5 for rVS, −15, 8, 16 for lDS in response to reward anticipation; MNI x, y, z = 9, 17, −11 for rVS, −9, 17, 1 for lVS, −18, 8, 16 for lDS in response to reward delivery. These graphs are provided for illustrative purposes only, and were not used for statistical inferences.
Table 1.
BOLD responses to reward anticipation and reward delivery in the ADHD and control groups.
Table 2.
The interaction effects of the group (control vs. ADHD) and condition (reward anticipation vs. reward delivery).
Figure 3.
Association between ventral striatal responses and the number of hyperactivity/impulsivity symptoms in the ADHD group.
Brain activation displays were generated by overlaying SPM t-maps from the second-level analyses on a MNI standard brain (p<.005 uncorrected). Reward anticipation (Cue A delay), t = 4.25 (p<.005, uncorrected, MNI local maxima: x, y, z = −6, 14, 4); reward delivery (Cue A reward), t = 5.43 (p = .04, FWE corrected, MNI local maxima: x, y, z = −21, 20, −5). The graphs depict the association between the mean parameter estimates of the peak cluster from the one-sample t-tests (y-axis) and the number of symptoms (x-axis) for each participant in the ADHD group. The graphs are provided for illustrative purposes only, and were not used for statistical inferences. MNI: Montreal Neurological Institute.