Information Technology Reference
In-Depth Information
nomenon
dynamical entrainment
(synchronization), and it has constituted the basis
for the development of epileptic seizure prediction algorithms.
17.2.2.2 Measure of Dynamical Entrainment
A statistical measure of synchronization of the dynamics between two electrodes
i
and
j
has been developed in the past. Specifically, the
T
ij
between electrode sites
i
and
j
for a measure of dynamics (e.g., STL
max
) at time
t
is defined as
D
t
ij
|
|
T
ij
=
ij
/
√
m
,
(17.2)
t
σ
ˆ
where
D
t
ij
and ˆ
t
ij
denote the sample mean and standard deviation respectively of
all
m
differences between a measure's values at electrodes
i
and
j
within a window
w
t
=[
σ
m
∗
10
t
t
,
t
−
.
24 s
]
moving over the measure's profiles. If the true mean
μ
ij
of
the differences
D
t
ij
is equal to 0, and
t
ij
are independent and normally distributed,
T
ij
is asymptotically distributed as the
t
-distribution with
σ
degrees of free-
dom. We have shown that these independence and normality conditions are satisfied
for STL
max
[10]. Therefore, we define desynchronization between electrode sites
i
and
j
when
T
ij
is significantly different from 0 at a significance level
(
m
−
1
)
. The desyn-
chronization condition between the electrode sites
i
and
j
, as detected by the paired
t
-test, is
α
T
ij
>
t
α
/
2
,
m
−
1
=
T
th
,
(17.3)
where
t
α
/
2
,
m
−
1
=
T
th
is the 100
(
1
−
α
/
2
)
critical value of the
t
-distribution with
m
−
1
degrees of freedom. If
T
ij
≤
t
α
/
2
,
m
−
1
(which means that we do not have satisfactory
statistical evidence at the
level for the differences of values of a measure between
electrode sites
i
and
j
be nonzero within the time window
w
t
), we consider sites
i
and
j
be synchronized with each other at time
t
.Using
α
α
=
0
.
01 and
m
=
60, the
threshold
T
th
=
662.
We then estimate the average level of synchronization, as measured by the av-
erage T-index across all possible entrained (synchronized) pairs of electrode sites
within a predefined time period over time. This average T-index is followed over
time to monitor the response of SE to AED treatment. In the following sections, for
simplicity, we denote these spatially averaged T-index values by “T-index.” Results
from this analysis in SE patients are presented next.
2
.
17.3 Results
From the EEG data per SE patient, the STL
max
profiles per recording site and the
T-index profiles over time per pair of recording sites were estimated. All synchro-
nized pairs of electrode sites within 10 min prior to administration of the first drug
