4 but no main effect of group F 258 053 ns or group by reward interaction

4 but no main effect of group f 258 053 ns or group

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> 1.4], but no main effect of group [ F (2,58) = 0.53, ns] or group-by-reward interaction effect [ F (4,56) = 1.13, ns]. This suggests that the different reward condi- tions similarly affected behavioral performance across groups. The following univariate ANOVAs showed that the significant reward effect was related to both speed ( p < 0.001, Cohen s d > 1.4) and accuracy ( p < 0.001, Cohen s d > 1.4). Regarding RT, post hoc contrasts revealed fastest RTs for SR, slowest RTs for NR and with the IR condition intermediate (all p s < 0.001, all Cohen s d s > 1.06). This indicates that incentive manipulations within the experimental task were successful. Post hoc contrasts for accuracy revealed the highest the correct re- sponse rate for SR, the lowest the correct response rate for IR and the NR condition intermediate (all p s < 0.004, all Cohen s d s > 0.77) (see Table 2 ). Although we intended to maintain an equal average accuracy across conditions and participants by adjusting the target duration accord- ing to individual trial-by-trial performance, our finding of different accuracy rates for the three incentive conditions is in line with prior studies [ 11 ]. Reward system responsiveness across both study groups Considering reward system responsiveness across both groups for the two high-level contrasts, i.e., SR > NR and IR > NR, the whole-brain analysis revealed robust brain activation (i.e., k 10) in ventral striatum (includ- ing Nacc), dorsal striatum (including caudate nucleus, and putamen), thalamus, amygdala, ACC, vmPFC, in- sula, and OFC (Fig. 2 ). Considering differential reward system activation for the two reward types, the IR > SR comparison showed greater BOLD responses in a cluster, comprising Nacc, caudate, thalamus, ACC, vmPFC, insula and OFC (MNI peak = 2, 42, 0; Z max = 9.16; k = 8047) as well as a cluster within posterior cingulate cortex (MNI peak = 0, 30, 28; Z max = 9.00; k = 166). The reversed comparison (i.e., SR > IR) yielded significant ac- tivation differences within right and left insula (MNI right- peak = 36, 18, 20; Z max = 5.18; k = 802, and MNI left-peak = 42, 18, 6; Z max = 4.87; k = 500). Reward system imbalance for interest reward versus social reward in ASD Following up our hypothesis of reward imbalance in ASD (i.e., enhanced reward system activation for CI re- ward, but diminished responsiveness for social reward), we specifically investigated group activation differences in response to IR versus SR. Using whole-brain cluster thresholding that strictly controls type I errors [ 32 ], neither the IR > SR contrast nor the SR > IR contrast re- vealed significant group activation differences. The additional ROI analyses, however, demonstrated that the right caudate (MNI peak = 12, 14, 14; t max = 3.14; Cohen s d = 0.84; k = 26) as well as the left caudate (MNI peak = 12, 6, 12; t max = 3.14; Cohen s d = 0.89; k = 96) were more ac- tive for IR than SR in youth with ASD relative to TDC; or put differently, the caudate was less active to SR than IR in ASD versus TDC (Fig. 3 ). None of the other a priori ROIs (i.e., Nacc, vmPFC, ACC, OFC, and insula) revealed significant group differences for IR > SR and SR > IR.
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