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These efficient clusters, noticed in the SCI group, could represent a compensative
mechanism as a consequence of the partial alteration in the primary motor areas
(MIF) due to the effects of the spinal cord injury. Moreover, the estimated
cortical networks are not structured like random networks. The statistical
contrasts performed by separate Z-tests (Bonferroni corrected for multiple
comparisons, p = 0.05) were summarized in the Table 10.1.
By inspecting the data presented in both Table 10.1 and Fig. 10.6, it is clear
that in general the cortical networks exhibited ordered and regular properties. In
particular, the global efficiency is significantly lower than the random mean
value, while the local efficiency of the SCI group is significantly higher than
random graphs in each band, meaning fault tolerance is privileged with respect to
global communication.
Table 10.1. Z-scores of E
g
and E
l
from the contrasts with 1000 random graphs.
Z
Values
SCI-
Theta
SCI-
Alpha
SCI-
Beta
SCI-
Gamma
Healthy-
Theta
Healthy-
Alpha
Healthy-
Beta
Healthy-
Gamma
E
g
-237.45
-250.13
-262.88
-267.07
-249.81
-238.21
-225.95
-223.4
E
l
57.714
53.314
57.025
38.936
-15.99
-11.051
7.163
21.674
10.4.2.
Time-varying cortical network during foot movement
The second study intends to evaluate the dynamics of the cerebral networks
during the preparation and the execution of the foot movement in healthy
subjects. Five voluntary subjects participated to the study (age, 26-32 years; five
males). For the EEG data acquisitions, the participants were comfortably seated
on a reclining chair in an electrically shielded and dimly lit room. They were
asked to perform a dorsal flexion of their right foot, whose preference was
previously attested by simple questionnaires (Chapman 1987). The movement
task was repeated every 8 seconds, in a self-paced manner and 200 single trials
were recorded by using 200 Hz of sampling frequency. Cortical activity was
estimated through high-resolution EEG techniques (see paragraph X.1). The
ROIs considered for the left (_L) and right (_R) hemisphere are the primary
motor areas of the foot (MF_L and MF_R), the proper supplementary motor
areas (SM_L and SM_R) and the cingulate motor areas (CM_L and CM_R). The
bilateral Brodmann areas 6 (6_L and 6_R), 7 (7_L and 7_R), 8 (8_L and 8_R),
9 (9_L and 9_R) and 40 (40_L and 40_R) were also considered. In order to
inspect the brain dynamics during the preparation and the execution of the
studied movement, a time segment of 2 seconds was analyzed, after having
