3  Results

3.1  Behavioural results

3.1.1  IQ
The 2-sub-test IQ scores were significantly lower in adolescents with ASD (M = 90.79, SD = 23.76) than in controls (M = 110.04, SD = 12.21), t(46) = –3.53, p = 0.001.

3.1.2  Accuracy
A 2 (emotion: happy, angry) × 2 (group: ASD, controls) repeated measures ANCOVA with IQ as a covariate showed a between-group effect on accuracy, F(1, 42) = 4.32, p = 0.04. Follow-up ANCOVAs revealed lower accuracy in responses (proportion correct) to angry faces (ASD: M = 0.87, SD = 0.10; Controls: M = 0.95, SD = 0.04; F(1, 42) = 5.53, p = 0.02). No other significant effects or interactions were found.

3.1.3  Response latency
A 2 (emotion: happy, angry) × 2 (group: ASD, controls) ANCOVA with IQ as a covariate showed no main or interaction effects on response latency.

3.2  MEG results: time course and source localization of neural activity
Significant between-group activations for happy and angry faces (p < 0.05, two-tailed, Sidak-corrected for multiple comparisons, 10,000 permutations) are listed in Table 1.

3.2.1  Angry
Apart from earlier and larger orbitofrontal activation in controls (75–125 ms; Fig. 2A), relative to adolescents with ASD, the other early activations (50–175 ms) in the presence of angry faces were all larger in the ASD group. These activations were lateralized to the left hemisphere, including the inferior frontal, inferior parietal and particularly the middle temporal areas. These latter two regions also showed greater activation in the ASD group later in the time-course: inferior parietal (275–325 ms) and middle temporal (350–400 ms) gyri. Otherwise to angry faces, there was significantly greater activity in the typically developing adolescents from 150 to 375 ms, involving the bilateral middle and orbital frontal areas, right middle temporal (250–350 ms), left ACC (225–275 ms; Fig. 2B), as well as right inferior temporal and supramarginal gyri (200–250 ms), and right posterior cingulate (325–375 ms; Fig. 2C).

3.2.2  Happy
To happy faces, the adolescents with ASD again showed early left-sided activity in the left middle temporal area (75–175 ms), and left angular (100–175 ms) and supramarginal gyri (150–200 ms). The left inferior temporal region also showed greater activation (275–325 ms) in the ASD group. Otherwise, there was extensive, greater activity in the control adolescents, almost entirely in the right hemisphere. The right inferior temporal gyrus showed sustained greater activity from 150 to 400 ms, with the middle temporal region more active from 225 to 275 ms. To the happy faces, controls also had greater activity than the ASD group in the right ACC (100–150 ms; Fig. 2D), supramarginal (150–200 ms) and angular (225–325 ms) gyri, in the superior, middle and inferior frontal areas between 200 and 400 ms, all in the right hemisphere, and in the right PCC (200–250 ms; 350–400 ms; Fig. 2E, Fig. 2F). The only left hemisphere regions with greater activation in the controls were in the left superior medial (100–150 ms) and orbital frontal cortices (150–200 ms) and in the left insula (350–400 ms; Fig. 2F).