Information Technology Reference
In-Depth Information
Λ
(
f
)
ij
π
(
f
)
=
(10.11)
ij
N
*
∑
=
Λ
(
f
)
Λ
(
f
)
ki
kj
k
1
The PDC from
j
to
i
,
π
ij
(
f
), describes the directional flow of information from the
activity in the ROI
x
j
(
t
) to the activity in
x
i
(
t
), whereupon common effects
produced by other ROIs
x
k
(
t
) on the latter are subtracted leaving only a
description that is exclusive from
x
j
(
t
) to
x
i
(
t
). PDC values are in the interval
[0 1] and the normalization condition:
N
2
( )
∑
=
π
f
=
1
(10.12)
ni
n
1
is verified. According to this condition,
π
ij
(
f
) represents the fraction of the time
evolution of ROI
j
directed to ROI
i
, as compared to all of
j
's interactions with
other ROIs. Figure 10.2 shows a schematic representation of the functional
connectivity estimation from a set of high-resolution EEG signals to the cortical
network.
Fig. 10.2. From a set of cortical time series the MVAR method estimates in the frequency domain
a functional connectivity pattern that can be modeled by means of a graph.
