<s>
Burst	B-Algorithm
suppression	I-Algorithm
is	O
an	O
electroencephalography	B-Application
(	O
EEG	B-Application
)	O
pattern	O
that	O
is	O
characterized	O
by	O
periods	O
of	O
high-voltage	O
electrical	O
activity	O
alternating	O
with	O
periods	O
of	O
no	O
activity	O
in	O
the	O
brain	O
.	O
</s>
<s>
The	O
burst	B-Algorithm
suppression	I-Algorithm
pattern	O
was	O
first	O
observed	O
by	O
Derbyshire	O
et	O
al	O
.	O
</s>
<s>
It	O
was	O
n't	O
until	O
after	O
the	O
early	O
1960s	O
that	O
the	O
burst	B-Algorithm
suppression	I-Algorithm
pattern	O
began	O
being	O
used	O
in	O
medical	O
settings	O
;	O
it	O
had	O
been	O
primarily	O
observed	O
in	O
animal	O
studies	O
and	O
psychosurgeries	O
.	O
</s>
<s>
In	O
1952	O
,	O
Henry	O
and	O
Scoville	O
recorded	O
the	O
electrical	O
activity	O
of	O
patients	O
during	O
lobotomy	O
and	O
found	O
the	O
burst	B-Algorithm
suppression	I-Algorithm
pattern	O
present	O
in	O
the	O
recorded	O
electrical	O
activity	O
.	O
</s>
<s>
The	O
pseudo-rhythmic	O
pattern	O
of	O
burst	B-Algorithm
suppression	I-Algorithm
is	O
dictated	O
by	O
extracellular	O
calcium	O
depletion	O
and	O
the	O
ability	O
of	O
neurons	O
to	O
restore	O
the	O
concentration	O
.	O
</s>
<s>
At	O
the	O
cellular	O
level	O
,	O
hyperpolarization	O
of	O
the	O
membrane	O
potential	O
of	O
cortical	O
neurons	O
reliably	O
precedes	O
any	O
overt	O
electroencephalographic	B-Application
activity	O
of	O
burst	B-Algorithm
suppression	I-Algorithm
.	O
</s>
<s>
This	O
hyperpolarization	O
,	O
which	O
has	O
been	O
attributed	O
to	O
an	O
increase	O
in	O
neuronal	O
membrane	O
potassium	O
conductance	O
,	O
has	O
been	O
hypothesized	O
to	O
play	O
a	O
major	O
role	O
in	O
the	O
induction	O
of	O
burst	B-Algorithm
suppression	I-Algorithm
,	O
supported	O
by	O
the	O
induction	O
of	O
burst	B-Algorithm
suppression	I-Algorithm
through	O
the	O
application	O
of	O
a	O
direct	O
acting	O
GABAA	O
agonist	O
,	O
muscimol	O
.	O
</s>
<s>
In	O
contrast	O
,	O
inhibition	O
is	O
diminished	O
when	O
burst	B-Algorithm
suppression	I-Algorithm
is	O
induced	O
through	O
the	O
use	O
of	O
isoflurane	O
.	O
</s>
<s>
Another	O
theory	O
is	O
that	O
alterations	O
in	O
brain	O
metabolism	O
regulate	O
activity	O
dependent	O
slow	O
modulation	O
of	O
ATP-gated	O
potassium	O
channel	O
conductance	O
which	O
induces	O
burst	B-Algorithm
suppression	I-Algorithm
.	O
</s>
<s>
However	O
,	O
modulating	O
inhibitory	O
activity	O
alone	O
may	O
not	O
be	O
sufficient	O
for	O
burst	B-Algorithm
suppression	I-Algorithm
,	O
and	O
modulation	O
in	O
excitatory	O
synaptic	O
efficiency	O
,	O
stemming	O
from	O
the	O
depletion	O
and	O
subsequent	O
recovery	O
of	O
interstitial	O
calcium	O
levels	O
,	O
could	O
contribute	O
to	O
the	O
induction	O
of	O
burst	B-Algorithm
suppression	I-Algorithm
.	O
</s>
<s>
Suppression	O
is	O
caused	O
by	O
the	O
absence	O
of	O
synaptic	O
activity	O
of	O
cortical	O
neurons	O
;	O
however	O
,	O
some	O
thalamocortical	O
neurons	O
exhibit	O
oscillations	O
in	O
the	O
delta	B-Algorithm
frequency	I-Algorithm
range	I-Algorithm
during	O
these	O
periods	O
.	O
</s>
<s>
The	O
burst	B-Algorithm
suppression	I-Algorithm
pattern	O
varies	O
with	O
the	O
brain	O
anesthetic	O
concentration	O
when	O
pharmacologically	O
inducing	O
coma	O
.	O
</s>
<s>
While	O
burst	B-Algorithm
suppression	I-Algorithm
has	O
typically	O
been	O
viewed	O
as	O
a	O
homogeneous	O
brain	O
state	O
,	O
recent	O
studies	O
have	O
shown	O
that	O
bursts	O
and	O
suppressions	O
can	O
occur	O
in	O
specific	O
regions	O
while	O
other	O
regions	O
are	O
unaffected	O
.	O
</s>
<s>
The	O
fact	O
that	O
the	O
burst	B-Algorithm
suppression	I-Algorithm
pattern	O
persists	O
after	O
a	O
patient	O
undergoes	O
cortical	O
deafferentation	O
indicates	O
that	O
burst	B-Algorithm
suppression	I-Algorithm
represents	O
an	O
intrinsic	O
dynamic	O
mode	O
of	O
cortex	O
.	O
</s>
<s>
Burst	B-Algorithm
suppression	I-Algorithm
patterns	O
can	O
be	O
classified	O
through	O
comparisons	O
of	O
burst	O
duration	O
and	O
inter-burst	O
intervals	O
,	O
maximum	O
peak	O
to	O
peak	O
voltage	O
,	O
and	O
the	O
ratio	O
of	O
power	O
in	O
high	O
versus	O
low	O
frequencies	O
.	O
</s>
<s>
(	O
Akrawi	O
et	O
al.	O
,	O
1996	O
)	O
Burst	B-Algorithm
suppression	I-Algorithm
with	O
identical	O
bursts	O
suggests	O
a	O
deterministic	O
process	O
of	O
burst	O
generation	O
,	O
whereas	O
other	O
burst	B-Algorithm
suppression	I-Algorithm
patterns	O
depend	O
on	O
stochastic	O
processes	O
.	O
</s>
<s>
Burst	B-Algorithm
suppression	I-Algorithm
with	O
identical	O
bursts	O
is	O
a	O
distinct	O
pathological	O
EEG	B-Application
pattern	O
that	O
is	O
typical	O
in	O
diffuse	O
cerebral	O
ischemia	O
and	O
is	O
associated	O
with	O
poor	O
outcomes	O
in	O
comatose	O
patients	O
after	O
cardiac	O
arrest	O
.	O
</s>
<s>
Bursts	O
are	O
identifiable	O
on	O
EEG	B-Application
readings	O
by	O
their	O
high	O
amplitude	O
(	O
75-250μV	O
)	O
,	O
typically	O
short	O
period	O
of	O
1	O
–	O
10	O
seconds	O
,	O
and	O
have	O
frequency	O
ranges	O
of	O
0	O
–	O
4Hz	O
( δ	O
)	O
and	O
4	O
–	O
7Hz	O
( θ	O
)	O
.	O
</s>
<s>
EEG	B-Application
recordings	O
of	O
burst-suppression	O
pattern	O
differ	O
between	O
adults	O
and	O
neonates	O
because	O
of	O
diverse	O
pattern	O
fluctuations	O
found	O
in	O
the	O
EEG	B-Application
of	O
neonates	O
.	O
</s>
<s>
Burst	B-Algorithm
suppression	I-Algorithm
patterns	O
also	O
occur	O
spontaneously	O
during	O
neonatal	O
development	O
,	O
rather	O
than	O
as	O
a	O
characteristic	O
of	O
inactivated	O
brains	O
as	O
in	O
adults	O
.	O
</s>
<s>
In	O
order	O
to	O
quantify	O
the	O
burst	B-Algorithm
suppression	I-Algorithm
pattern	O
,	O
the	O
EEG	B-Application
signal	O
must	O
be	O
subject	O
to	O
segmentation	O
.	O
</s>
<s>
These	O
processes	O
separates	O
burst	O
and	O
suppression	O
episodes	O
based	O
on	O
EEG	B-Application
features	O
such	O
as	O
entropies	O
,	O
non-linear-energy-operator	O
,	O
voltage	O
variance	O
,	O
or	O
adaptation	O
of	O
constant	O
false	O
alarm	O
rate	O
(	O
CFAR	O
)	O
algorithm	O
,	O
etc	O
.	O
</s>
<s>
Quantifying	O
the	O
burst	B-Algorithm
suppression	I-Algorithm
pattern	O
allows	O
for	O
calculation	O
of	O
the	O
burst	B-Algorithm
suppression	I-Algorithm
ratio	O
(	O
BSR	O
)	O
by	O
assigning	O
binary	O
values	O
of	O
0	O
to	O
bursts	O
and	O
1	O
to	O
suppression	O
episodes	O
.	O
</s>
<s>
Thus	O
,	O
a	O
burst	B-Algorithm
suppression	I-Algorithm
ratio	O
of	O
1	O
is	O
associated	O
with	O
a	O
state	O
of	O
the	O
brain	O
that	O
shows	O
no	O
electrical	O
activity	O
,	O
while	O
a	O
ratio	O
of	O
0	O
indicates	O
that	O
the	O
brain	O
is	O
active	O
.	O
</s>
<s>
The	O
burst	B-Algorithm
suppression	I-Algorithm
ratio	O
measures	O
the	O
amount	O
of	O
time	O
within	O
an	O
interval	O
spent	O
in	O
the	O
suppressed	O
state	O
.	O
</s>
<s>
This	O
ratio	O
increases	O
as	O
the	O
brain	O
becomes	O
increasingly	O
inactive	O
until	O
the	O
brain	O
's	O
EEG	B-Application
signal	O
flatlines	O
,	O
represented	O
by	O
a	O
burst	B-Algorithm
suppression	I-Algorithm
ratio	O
equal	O
to	O
1	O
.	O
</s>
<s>
Because	O
of	O
the	O
direct	O
relationship	O
between	O
burst	B-Algorithm
suppression	I-Algorithm
ratio	O
and	O
brain	O
inactivity	O
,	O
the	O
ratio	O
is	O
an	O
indicator	O
of	O
suppression	O
intensity	O
.	O
</s>
<s>
Using	O
the	O
same	O
binary	O
assignments	O
to	O
the	O
burst	B-Algorithm
suppression	I-Algorithm
pattern	O
,	O
another	O
measure	O
of	O
the	O
depth	O
of	O
burst	B-Algorithm
suppression	I-Algorithm
,	O
the	O
burst	B-Algorithm
suppression	I-Algorithm
probability	O
(	O
BSP	O
)	O
,	O
can	O
be	O
determined	O
.	O
</s>
<s>
where	O
xi	O
is	O
the	O
brain	O
's	O
suppression	O
state	O
at	O
time	O
iΔ	O
,	O
with	O
Δ	B-Algorithm
representing	O
intervals	O
for	O
analysis	O
,	O
and	O
ranges	O
across	O
all	O
real	O
numbers	O
.	O
</s>
<s>
Because	O
the	O
burst	B-Algorithm
suppression	I-Algorithm
pattern	O
is	O
characteristic	O
of	O
inactivated	O
brains	O
,	O
the	O
pattern	O
can	O
be	O
used	O
as	O
a	O
marker	O
for	O
the	O
level	O
of	O
coma	O
a	O
patient	O
is	O
in	O
,	O
with	O
persistence	O
of	O
the	O
pattern	O
commonly	O
associated	O
with	O
poor	O
prognosis	O
.	O
</s>
<s>
Note	O
,	O
however	O
,	O
that	O
there	O
is	O
evidence	O
linking	O
sedation-induced	O
burst	B-Algorithm
suppression	I-Algorithm
with	O
positive	O
outcomes	O
in	O
patients	O
recovering	O
from	O
coma	O
following	O
traumatic	O
brain	O
injury	O
,	O
suggesting	O
a	O
neuroprotective	O
effect	O
.	O
</s>
<s>
The	O
burst	B-Algorithm
suppression	I-Algorithm
pattern	O
can	O
also	O
be	O
used	O
to	O
track	O
ascent	O
into	O
and	O
descent	O
out	O
of	O
hypothermia	O
through	O
observing	O
changes	O
in	O
the	O
pattern	O
.	O
</s>
<s>
Monitoring	O
the	O
burst	B-Algorithm
suppression	I-Algorithm
ratio	O
aids	O
medical	O
personnel	O
in	O
adjusting	O
suppression	O
intensity	O
for	O
therapeutic	O
purposes	O
;	O
however	O
,	O
medical	O
personnel	O
currently	O
rely	O
on	O
visually	O
monitoring	O
the	O
EEG	B-Application
and	O
arbitrarily	O
assessing	O
the	O
depth	O
of	O
burst	B-Algorithm
suppression	I-Algorithm
.	O
</s>
<s>
Not	O
only	O
is	O
the	O
evaluation	O
of	O
the	O
EEG	B-Application
signal	O
for	O
burst	B-Algorithm
suppression	I-Algorithm
done	O
manually	O
,	O
but	O
also	O
the	O
infusion	O
rate	O
of	O
anesthetic	O
to	O
adjust	O
suppression	O
intensity	O
.	O
</s>
<s>
This	O
is	O
done	O
through	O
the	O
use	O
of	O
measures	O
such	O
as	O
burst	B-Algorithm
suppression	I-Algorithm
probability	O
for	O
real-time	O
tracking	O
of	O
burst	B-Algorithm
suppression	I-Algorithm
or	O
brain	B-Application
–	I-Application
machine	I-Application
interfaces	I-Application
to	O
automate	O
maintaining	O
proper	O
levels	O
of	O
inactivity	O
.	O
</s>
