Supplementary Text s3

Supplementary text:

Methods:

Participants: Originally 81 subjects were scanned. Seven boys with ADHD scored above clinical threshold for SCQ and 10 boys with ASD scored higher than 7 on the SDQ as well as high on the Conners CPRS-R. These patients were excluded from the analysis. Four of these patients were also outliers in one or more performance measures across all 4 delays. Three of these patients had also to be excluded due to high movement artefacts.

Description of fMRI preprocessing:

Data were first processed (Bullmore et al., 1999) to minimize motion related artifacts. A 3D volume consisting of the average intensity at each voxel over the whole experiment was calculated and used as a template. The 3D image volume at each timepoint was then realigned to this template by computing the combination of rotations (around the x y and z axes) and translations (in x y and z) that maximised the correlation between the image intensities of the volume in question and the template. Following realignment, data were then smoothed using a Gaussian filter (FWHM 2.354 * in-plane fMRI voxel size mm) to improve the signal to noise characteristics of the images (Bullmore et al., 1999).

References: Bullmore, E.T., Brammer, M. J., Rabe-Hesketh, S., Curtis, V., Morris, R. G., Williams, S. C. R., Sharma, T. and McGuire, P. K. (1999a) Methods for diagnosis and treatment of stimulus-correlated motion in generic brain activation studies using fMRI. Human Brain Mapping 7,38- 48. Supplementary Fig 1. Horizontal slices showing split plot ANOVA effects of increasing delay on brain activation for all subjects. The right side corresponds to the right side of the image. Supplementary Table 1. Sample characteristics for healthy control boys and patients with ADHD and ASD. Variables Controls (20) ADHD (20) ASD (20) Mean (SD) Mean (SD) Mean (SD) Age (months) 176.2 (26.8) 168.0 (20.6) 176.1 (20.2) IQ 114 (8.1) 108.2 (10.7) 112.9 (14.3) Handedness 89.8 (15.2) 85.4 (20.3) 93.3 (9.4) SDQ - Hyperactive/Inattentive Subscale 2.4 (1.7) 8.4 (1.4) 5.4 (1.8) SDQ - Emotional Distress Subscale 0.9 (2) 4.2 (2.9) 4.2 (2.6) SDQ - Conduct Subscale 0.8 (1.2) 5.2 (2.4) 1.9 (1.8) SDQ – Peer Relations Subscale 0.4 (0.7) 3.6 (2.2) 5.9 (2.2) SDQ – Prosocial Behaviour Subscale 8.6 (2.5) 5.8 (2.7) 4.5 (2.4) SDQ – Total scores 4 (4) 21.4 (6) 17.2 (5) SCQ Total 2.4 (2.5) 8.7 (5.1) 25.6 (5.1) CPRS-R Total T score 47 (8) 79 (9) 70 (11) ADOS Communication scores - - 3.8 (1) ADOS Social scores - - 9.5 (2) ADOS Communication and social scores - - 13.3 (3) ADOS Imagination scores - - 0.7 (.7) ADOS stereotyped behaviour scores - - 1.7 (1.6) ADI social scores - - 22 (5) ADI communication scores - - 17 (5) ADI repetitive behaviour scores - - 6.6 (2) Abbreviations: IQ = intelligence quotient as assessed with the Wechsler Abbreviated Scale of Intelligence; Handedness score as assessed by the Edinburgh Handedness Questionnaire; SDQ = Strength and Difficulty Questionnaire; SCQ: Social and Communication Questionnaire; CPRS-R= Conners’ Parent Rating Score-Revised Supplementary Table 2. Performance measures for the sustained attention task for each delay for boys with ADHD, ASD and healthy controls.

Performance measure Controls ADHD ASD Delay Mean (SD) Mean (SD) Mean (SD) MRT 0.5s 299 (43) 301 (78) 309 (60) 2s 383 (37) 430 (39) 416 (52) 5s 388 (52) 415 (52) 410 (59) 8s 390 (50) 427 (62) 421 (66) SDintrasubject 0.5s 79 (35) 116 (39) 91 (48) 2s 69 (26) 98 (30) 82 (45) 5s 64 (25) 90 (29) 75 (37) 8s 70 (25) 104 (32) 74 (42) Premature errors 0.5s 13 (25) 24 (25) 13 (28) 2s 5 (6) 8 (7) 6 (7) 5s 6 (7) 8 (8) 5 (5) 8s 5 (7) 9 (9) 9 (17) Omission errors 0.5s .6 (1.6) 2 (3) 3.2 (10) 2s .3 (.7) .3 (.6) .4 (1.3) 5s .2 (.9) .1 (.4) .3 (.7) 8s .05 (1) .05 (.2) .2 (.9) Abbreviations: MRT = Mean Reaction Time (in ms); SDintrasubject: intrasubject variability of response of reaction time (in ms).