<s>
Dynamic	B-Algorithm
functional	I-Algorithm
connectivity	I-Algorithm
(	O
DFC	O
)	O
refers	O
to	O
the	O
observed	O
phenomenon	O
that	O
functional	O
connectivity	O
changes	O
over	O
a	O
short	O
time	O
.	O
</s>
<s>
Dynamic	B-Algorithm
functional	I-Algorithm
connectivity	I-Algorithm
is	O
a	O
recent	O
expansion	O
on	O
traditional	O
functional	O
connectivity	O
analysis	O
which	O
typically	O
assumes	O
that	O
functional	O
networks	O
are	O
static	O
in	O
time	O
.	O
</s>
<s>
The	O
primary	O
tool	O
for	O
analyzing	O
DFC	O
is	O
fMRI	B-Algorithm
,	O
but	O
DFC	O
has	O
also	O
been	O
observed	O
with	O
several	O
other	O
mediums	O
.	O
</s>
<s>
DFC	O
is	O
a	O
recent	O
development	O
within	O
the	O
field	O
of	O
functional	B-Algorithm
neuroimaging	I-Algorithm
whose	O
discovery	O
was	O
motivated	O
by	O
the	O
observation	O
of	O
temporal	O
variability	O
in	O
the	O
rising	O
field	O
of	O
steady	O
state	O
connectivity	O
research	O
.	O
</s>
<s>
This	O
type	O
of	O
connectivity	O
was	O
discovered	O
in	O
the	O
mid-1990s	O
and	O
has	O
been	O
seen	O
primarily	O
using	O
fMRI	B-Algorithm
and	O
Positron	B-Application
emission	I-Application
tomography	I-Application
.	O
</s>
<s>
Functional	O
connectivity	O
is	O
usually	O
measured	O
during	O
resting	B-Algorithm
state	I-Algorithm
fMRI	I-Algorithm
and	O
is	O
typically	O
analyzed	O
in	O
terms	O
of	O
correlation	O
,	O
coherence	O
,	O
and	O
spatial	O
grouping	O
based	O
on	O
temporal	O
similarities	O
.	O
</s>
<s>
Analysis	O
of	O
dynamic	B-Algorithm
functional	I-Algorithm
connectivity	I-Algorithm
has	O
shown	O
that	O
far	O
from	O
being	O
completely	O
static	O
,	O
the	O
functional	O
networks	O
of	O
the	O
brain	O
fluctuate	O
on	O
the	O
scale	O
of	O
seconds	O
to	O
minutes	O
.	O
</s>
<s>
Sliding	O
window	O
analysis	O
is	O
the	O
most	O
common	O
method	O
used	O
in	O
the	O
analysis	O
of	O
functional	O
connectivity	O
,	O
first	O
introduced	O
by	O
Sakoglu	O
and	O
Calhoun	O
in	O
2009	O
,	O
and	O
applied	O
to	O
schizophrenia	B-Application
.	O
</s>
<s>
Sliding	O
window	O
analysis	O
is	O
performed	O
by	O
conducting	O
analysis	O
on	O
a	O
set	O
number	O
of	O
scans	O
in	O
an	O
fMRI	B-Algorithm
session	O
.	O
</s>
<s>
One	O
of	O
the	O
first	O
methods	O
ever	O
used	O
to	O
analyze	O
DFC	O
was	O
pattern	O
analysis	O
of	O
fMRI	B-Algorithm
images	O
to	O
show	O
that	O
there	O
are	O
patterns	O
of	O
activation	O
in	O
spatially	O
separated	O
brain	O
regions	O
that	O
tend	O
to	O
have	O
synchronous	O
activity	O
.	O
</s>
<s>
Repeating	O
patterns	O
of	O
network	O
information	O
have	O
been	O
suggested	O
to	O
account	O
for	O
25	O
–	O
50%	O
of	O
the	O
variance	O
in	O
fMRI	B-Algorithm
BOLD	O
data	O
.	O
</s>
<s>
Departing	O
from	O
the	O
traditional	O
approaches	O
,	O
recently	O
an	O
efficient	O
method	O
was	O
introduced	O
to	O
analyze	O
rapidly	O
changing	O
functional	O
activations	O
patterns	O
which	O
transforms	O
the	O
fMRI	B-Algorithm
BOLD	O
data	O
into	O
a	O
point	O
process	O
.	O
</s>
<s>
Time-frequency	B-Algorithm
analysis	I-Algorithm
has	O
been	O
proposed	O
as	O
an	O
analysis	O
method	O
that	O
is	O
capable	O
of	O
overcoming	O
many	O
of	O
the	O
challenges	O
associated	O
with	O
sliding	O
windows	O
.	O
</s>
<s>
The	O
wavelet	B-Algorithm
transform	I-Algorithm
has	O
been	O
used	O
to	O
conduct	O
DFC	O
analysis	O
that	O
has	O
validated	O
the	O
existence	O
of	O
DFC	O
by	O
showing	O
its	O
significant	O
changes	O
in	O
time	O
.	O
</s>
<s>
Independent	B-Algorithm
component	I-Algorithm
analysis	I-Algorithm
has	O
become	O
one	O
of	O
the	O
most	O
common	O
methods	O
of	O
network	O
generation	O
in	O
steady	O
state	O
functional	O
connectivity	O
.	O
</s>
<s>
ICA	O
divides	O
fMRI	B-Algorithm
signal	O
into	O
several	O
spatial	O
components	O
that	O
have	O
similar	O
temporal	O
patterns	O
.	O
</s>
<s>
More	O
recently	O
,	O
ICA	O
has	O
been	O
used	O
to	O
divide	O
fMRI	B-Algorithm
data	O
into	O
different	O
temporal	O
components	O
.	O
</s>
<s>
This	O
has	O
been	O
termed	O
temporal	O
ICA	O
and	O
it	O
has	O
been	O
used	O
to	O
plot	O
network	O
behavior	O
that	O
accounts	O
for	O
25%	O
of	O
variability	O
in	O
the	O
correlation	O
of	O
anatomical	O
nodes	O
in	O
fMRI	B-Algorithm
.	O
</s>
<s>
Noise	O
in	O
fMRI	B-Algorithm
can	O
arise	O
from	O
a	O
variety	O
of	O
different	O
factors	O
including	O
heart	O
beat	O
,	O
changes	O
in	O
the	O
blood	O
brain	O
barrier	O
,	O
characteristics	O
of	O
the	O
acquiring	O
scanner	O
,	O
or	O
unintended	O
effects	O
of	O
analysis	O
.	O
</s>
<s>
Some	O
researchers	O
have	O
proposed	O
that	O
the	O
variability	O
in	O
functional	O
connectivity	O
in	O
fMRI	B-Algorithm
studies	O
is	O
consistent	O
with	O
the	O
variability	O
that	O
one	O
would	O
expect	O
from	O
simply	O
analyzing	O
random	O
data	O
.	O
</s>
<s>
This	O
complaint	O
that	O
DFC	O
may	O
reflect	O
only	O
noise	O
has	O
been	O
recently	O
lessened	O
by	O
the	O
observation	O
of	O
electrical	O
basis	O
to	O
fMRI	B-Algorithm
DFC	O
data	O
and	O
behavioral	O
relevance	O
of	O
DFC	O
characteristics	O
.	O
</s>
<s>
In	O
addition	O
to	O
complaints	O
that	O
DFC	O
may	O
be	O
a	O
product	O
of	O
scanner	O
noise	O
,	O
observed	O
DFC	O
could	O
be	O
criticized	O
based	O
on	O
the	O
indirect	O
nature	O
of	O
fMRI	B-Algorithm
which	O
is	O
used	O
to	O
observe	O
it	O
.	O
</s>
<s>
fMRI	B-Algorithm
data	O
is	O
collected	O
by	O
quickly	O
acquiring	O
a	O
sequence	O
of	O
MRI	O
images	O
in	O
time	O
using	O
echo	O
planar	O
imaging	O
.	O
</s>
<s>
Because	O
of	O
its	O
indirect	O
nature	O
,	O
fMRI	B-Algorithm
data	O
in	O
DFC	O
studies	O
could	O
be	O
criticized	O
as	O
potentially	O
being	O
a	O
reflection	O
of	O
non	O
neural	O
information	O
.	O
</s>
<s>
This	O
concern	O
has	O
been	O
alleviated	O
recently	O
by	O
the	O
observed	O
correlation	O
between	O
fMRI	B-Algorithm
DFC	O
and	O
simultaneously	O
acquired	O
electrophysiology	O
data	O
.	O
</s>
<s>
fMRI	B-Algorithm
is	O
the	O
primary	O
means	O
of	O
investigating	O
DFC	O
.	O
</s>
<s>
This	O
presents	O
unique	O
challenges	O
because	O
fMRI	B-Algorithm
has	O
fairly	O
low	O
temporal	O
resolution	O
,	O
typically	O
0.5Hz	O
,	O
and	O
is	O
only	O
an	O
indirect	O
measure	O
of	O
neural	O
activity	O
.	O
</s>
<s>
The	O
indirect	O
nature	O
of	O
fMRI	B-Algorithm
analysis	O
suggests	O
that	O
validation	O
is	O
needed	O
to	O
show	O
that	O
findings	O
from	O
fMRI	B-Algorithm
are	O
actually	O
relevant	O
and	O
reflective	O
of	O
neural	O
activity	O
.	O
</s>
<s>
Electroencephalography	B-Application
(	O
EEG	B-Application
)	O
has	O
also	O
been	O
used	O
in	O
humans	O
to	O
both	O
validate	O
and	O
interpret	O
observations	O
made	O
in	O
DFC	O
.	O
</s>
<s>
EEG	B-Application
has	O
poor	O
spatial	O
resolution	O
because	O
it	O
is	O
only	O
able	O
to	O
acquire	O
data	O
on	O
the	O
surface	O
of	O
the	O
scalp	O
,	O
but	O
it	O
is	O
reflective	O
of	O
broad	O
electrical	O
activity	O
from	O
many	O
neurons	O
.	O
</s>
<s>
EEG	B-Application
has	O
been	O
used	O
simultaneously	O
with	O
fMRI	B-Algorithm
to	O
account	O
for	O
some	O
of	O
the	O
inter	O
scan	O
variance	O
in	O
FC	O
.	O
</s>
<s>
EEG	B-Application
has	O
also	O
been	O
used	O
to	O
show	O
that	O
changes	O
in	O
FC	O
are	O
related	O
to	O
broad	O
brain	O
states	O
observed	O
in	O
EEG	B-Application
.	O
</s>
<s>
Magnetoencephalography	B-Algorithm
(	O
MEG	O
)	O
can	O
be	O
used	O
to	O
measure	O
the	O
magnetic	O
fields	O
produced	O
by	O
electrical	O
activity	O
in	O
the	O
brain	O
.	O
</s>
<s>
MEG	O
has	O
high	O
temporal	O
resolution	O
and	O
has	O
generally	O
higher	O
spatial	O
resolution	O
than	O
EEG	B-Application
.	O
</s>
<s>
Resting	B-Algorithm
state	I-Algorithm
studies	O
with	O
MEG	O
are	O
still	O
limited	O
by	O
spatial	O
resolution	O
,	O
but	O
the	O
modality	O
has	O
been	O
used	O
to	O
show	O
that	O
resting	B-Algorithm
state	I-Algorithm
networks	O
move	O
through	O
periods	O
of	O
low	O
and	O
high	O
levels	O
of	O
correlation	O
.	O
</s>
<s>
Traditionally	O
,	O
fMRI	B-Algorithm
studies	O
have	O
focused	O
on	O
the	O
magnitude	O
of	O
activation	O
in	O
brain	O
regions	O
as	O
a	O
predictor	O
of	O
performance	O
,	O
but	O
recent	O
research	O
has	O
shown	O
that	O
correlation	O
between	O
networks	O
as	O
measured	O
with	O
sliding	O
window	O
analysis	O
is	O
an	O
even	O
stronger	O
predictor	O
of	O
performance	O
.	O
</s>
<s>
Individual	O
differences	O
in	O
functional	O
connectivity	O
variability	O
(	O
FCV	O
)	O
across	O
sliding	O
windows	O
within	O
fMRI	B-Algorithm
scans	I-Algorithm
have	O
been	O
shown	O
to	O
correlate	O
with	O
the	O
tendency	O
to	O
attend	O
to	O
pain	O
.	O
</s>
<s>
Static	O
functional	O
connectivity	O
has	O
been	O
shown	O
to	O
be	O
significantly	O
related	O
to	O
a	O
variety	O
of	O
diseases	O
such	O
as	O
depression	O
,	O
schizophrenia	B-Application
,	O
and	O
Alzheimer	O
's	O
disease	O
.	O
</s>
<s>
Patients	O
with	O
Schizophrenia	B-Application
have	O
less	O
frequent	O
state	O
changes	O
than	O
healthy	O
patients	O
,	O
and	O
this	O
result	O
has	O
led	O
to	O
the	O
suggestion	O
that	O
the	O
disease	O
is	O
related	O
to	O
patients	O
being	O
stuck	O
in	O
certain	O
brain	O
states	O
where	O
the	O
brain	O
is	O
unable	O
to	O
respond	O
quickly	O
to	O
different	O
queues	O
.	O
</s>
<s>
Also	O
,	O
a	O
study	O
in	O
the	O
visual	O
sensory	O
network	O
showed	O
that	O
schizophrenia	B-Application
subjects	O
spent	O
more	O
time	O
than	O
the	O
healthy	O
subjects	O
in	O
a	O
state	O
in	O
which	O
the	O
connectivity	O
between	O
the	O
middle	O
temporal	O
gyrus	O
and	O
other	O
regions	O
of	O
the	O
visual	O
sensory	O
network	O
is	O
highly	O
negative	O
.	O
</s>
