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 ).