3.3 Group differences in the MRCP
A robust MRCP was present over frontal and left parietal scalp regions in both ASD and control groups, consistent with dipolar electrical activity generated from left motor cortex and surrounding regions contralateral to the motor effector (Figure 3 ). This was seen as a ramping up period prior to the button press with an initial peak at approximately 100 ms prior to the response, and a secondary peak shortly after the response (3B – E ). This response returned to baseline at approximately 125 ms after the response and was followed by a deflection that peaked at about 210ms. While both participant groups showed a similar morphology of response, this was of smaller amplitude in the ASD group over the frontal and ipsilateral posterior scalp regions in the timewindow of the late BP (3B – E )
To investigate group differences in late BP, MP, and RAP components of the classic MRCP, general linear mixed models (GLMM) were conducted on individual participant amplitude values extracted from each timewindow from electrodes Fz and P3. Analyses revealed a significant group-by-electrode interaction in the late BP period (F(1, 3818.014) = 24.858, p < 0.001), indicating that ASD participants show lower-amplitude componentry relative to TD at both electrode sites (Table 3A ), as well as an expected main effect of electrode (F(2,3818.014) = 333.027, p < 0.001).
The exploratory SCP analysis revealed additional significant group differences across several scalp regions and time windows (3F ). Between -250 and -50 ms prior to response onset, significant group differences were observed primarily over fronto-central and bilateral parietal scalp regions. Between approximately -10 ms before the response and 100 ms after the response, significant differences were observed over fronto-central, right parietal, and right temporal scalp. Representative electrodes illustrating between-group differences are provided in 3C (fronto-central electrode FCz) and 3E(right parietal electrode P6).
To further illustrate the distribution of electrical potential across the entire scalp and visually compare these across groups, topographic representations of response-locked ERPs were generated per group (3G – I ). Topographic visualizations of 50 ms time windows in which the SCPs revealed statistically significant differences based on the statistical cluster plot (3F ) are given. These time bins encompassed -250 to -200 ms prior to response onset (3G ), -150 ms to -100 ms before the response (3H ), and 0 to 50 ms after the response (3I ).