<s>
An	O
evoked	B-Algorithm
potential	I-Algorithm
or	O
evoked	B-Algorithm
response	I-Algorithm
is	O
an	O
electrical	O
potential	O
in	O
a	O
specific	O
pattern	O
recorded	O
from	O
a	O
specific	O
part	O
of	O
the	O
nervous	O
system	O
,	O
especially	O
the	O
brain	O
,	O
of	O
a	O
human	O
or	O
other	O
animals	O
following	O
presentation	O
of	O
a	O
stimulus	O
such	O
as	O
a	O
light	O
flash	O
or	O
a	O
pure	O
tone	O
.	O
</s>
<s>
Evoked	B-Algorithm
potential	I-Algorithm
is	O
distinct	O
from	O
spontaneous	O
potentials	O
as	O
detected	O
by	O
electroencephalography	B-Application
(	O
EEG	B-Application
)	O
,	O
electromyography	O
(	O
EMG	O
)	O
,	O
or	O
other	O
electrophysiologic	B-Application
recording	O
method	O
.	O
</s>
<s>
Evoked	B-Algorithm
potential	I-Algorithm
amplitudes	B-Application
tend	O
to	O
be	O
low	O
,	O
ranging	O
from	O
less	O
than	O
a	O
microvolt	O
to	O
several	O
microvolts	O
,	O
compared	O
to	O
tens	O
of	O
microvolts	O
for	O
EEG	B-Application
,	O
millivolts	O
for	O
EMG	O
,	O
and	O
often	O
close	O
to	O
20	O
millivolts	O
for	O
ECG	B-Application
.	O
</s>
<s>
To	O
resolve	O
these	O
low-amplitude	O
potentials	O
against	O
the	O
background	O
of	O
ongoing	O
EEG	B-Application
,	O
ECG	B-Application
,	O
EMG	O
,	O
and	O
other	O
biological	O
signals	O
and	O
ambient	O
noise	O
,	O
signal	O
averaging	O
is	O
usually	O
required	O
.	O
</s>
<s>
Usually	O
the	O
term	O
"	O
evoked	B-Algorithm
potential	I-Algorithm
"	O
is	O
reserved	O
for	O
responses	O
involving	O
either	O
recording	O
from	O
,	O
or	O
stimulation	O
of	O
,	O
central	O
nervous	O
system	O
structures	O
.	O
</s>
<s>
Thus	O
evoked	O
compound	O
motor	O
action	O
potentials	O
(	O
CMAP	O
)	O
or	O
sensory	O
nerve	O
action	O
potentials	O
(	O
SNAP	O
)	O
as	O
used	O
in	O
nerve	O
conduction	O
studies	O
(	O
NCS	O
)	O
are	O
generally	O
not	O
thought	O
of	O
as	O
evoked	B-Algorithm
potentials	I-Algorithm
,	O
though	O
they	O
do	O
meet	O
the	O
above	O
definition	O
.	O
</s>
<s>
Evoked	B-Algorithm
potential	I-Algorithm
is	O
different	O
from	O
event-related	B-Algorithm
potential	I-Algorithm
(	O
ERP	O
)	O
,	O
although	O
the	O
terms	O
are	O
sometimes	O
used	O
synonymously	O
,	O
because	O
ERP	O
has	O
higher	O
latency	O
,	O
and	O
is	O
associated	O
with	O
higher	O
cognitive	O
processing	O
.	O
</s>
<s>
Evoked	B-Algorithm
potentials	I-Algorithm
are	O
mainly	O
classified	O
by	O
the	O
type	O
of	O
stimulus	O
:	O
somatosensory	O
,	O
auditory	O
,	O
visual	O
.	O
</s>
<s>
An	O
evoked	B-Algorithm
potential	I-Algorithm
is	O
the	O
electrical	O
response	O
of	O
the	O
brain	O
to	O
a	O
sensory	O
stimulus	O
.	O
</s>
<s>
Regan	O
constructed	O
an	O
analogue	O
Fourier	O
series	O
analyzer	O
to	O
record	O
harmonics	O
of	O
the	O
evoked	B-Algorithm
potential	I-Algorithm
to	O
flickering	O
(	O
sinusoidally	O
modulated	O
)	O
light	O
.	O
</s>
<s>
This	O
allowed	O
him	O
to	O
demonstrate	O
that	O
the	O
brain	O
attained	O
a	O
steady-state	O
regime	O
in	O
which	O
the	O
amplitude	B-Application
and	O
phase	O
of	O
the	O
harmonics	O
(	O
frequency	O
components	O
)	O
of	O
the	O
response	O
were	O
approximately	O
constant	O
over	O
time	O
.	O
</s>
<s>
By	O
analogy	O
with	O
the	O
steady-state	O
response	O
of	O
a	O
resonant	O
circuit	O
that	O
follows	O
the	O
initial	O
transient	O
response	O
he	O
defined	O
an	O
idealized	O
steady-state	B-Algorithm
evoked	I-Algorithm
potential	I-Algorithm
(	O
SSEP	O
)	O
as	O
a	O
form	O
of	O
response	O
to	O
repetitive	O
sensory	O
stimulation	O
in	O
which	O
the	O
constituent	O
frequency	O
components	O
of	O
the	O
response	O
remain	O
constant	O
with	O
time	O
in	O
both	O
amplitude	B-Application
and	O
phase	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
properties	O
of	O
the	O
high-frequency	O
flicker	O
SSEP	O
(	O
whose	O
peak	O
amplitude	B-Application
is	O
near	O
40	O
–	O
50Hz	O
)	O
correspond	O
to	O
the	O
properties	O
of	O
the	O
subsequently	O
discovered	O
magnocellular	O
neurons	O
in	O
the	O
retina	O
of	O
the	O
macaque	O
monkey	O
,	O
while	O
the	O
properties	O
of	O
the	O
medium-frequency	O
flicker	O
SSEP	O
(	O
whose	O
amplitude	B-Application
peak	O
is	O
near	O
15	O
–	O
20Hz	O
)	O
correspond	O
to	O
the	O
properties	O
of	O
parvocellular	O
neurons	O
.	O
</s>
<s>
Since	O
a	O
SSEP	O
can	O
be	O
completely	O
described	O
in	O
terms	O
of	O
the	O
amplitude	B-Application
and	O
phase	O
of	O
each	O
frequency	O
component	O
it	O
can	O
be	O
quantified	O
more	O
unequivocally	O
than	O
an	O
averaged	O
transient	O
evoked	B-Algorithm
potential	I-Algorithm
.	O
</s>
<s>
Because	O
of	O
the	O
high-frequency	O
rolloff	B-Algorithm
of	O
the	O
SSEP	O
,	O
high	O
frequency	O
stimulation	O
can	O
produce	O
a	O
near-sinusoidal	O
SSEP	O
waveform	O
,	O
but	O
this	O
is	O
not	O
germane	O
to	O
the	O
definition	O
of	O
a	O
SSEP	O
.	O
</s>
<s>
By	O
using	O
zoom-FFT	O
to	O
record	O
SSEPs	O
at	O
the	O
theoretical	O
limit	O
of	O
spectral	O
resolution	O
ΔF	O
(	O
where	O
ΔF	O
in	O
Hz	O
is	O
the	O
reciprocal	O
of	O
the	O
recording	O
duration	O
in	O
seconds	O
)	O
Regan	O
and	O
Regan	O
discovered	O
that	O
the	O
amplitude	B-Application
and	O
phase	O
variability	O
of	O
the	O
SSEP	O
can	O
be	O
sufficiently	O
small	O
that	O
the	O
bandwidth	O
of	O
the	O
SSEP	O
's	O
constituent	O
frequency	O
components	O
can	O
be	O
at	O
the	O
theoretical	O
limit	O
of	O
spectral	O
resolution	O
up	O
to	O
at	O
least	O
a	O
500-second	O
recording	O
duration	O
(	O
0.002Hz	O
in	O
this	O
case	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
visual	O
stimulus	O
was	O
flickered	O
at	O
Fv	O
Hz	O
and	O
a	O
simultaneously	O
presented	O
auditory	O
tone	O
was	O
amplitude	B-Application
modulated	O
at	O
Fa	O
Hz	O
.	O
</s>
<s>
A	O
plot	O
of	O
,	O
for	O
example	O
,	O
response	O
amplitude	B-Application
versus	O
the	O
check	O
size	O
of	O
a	O
stimulus	O
checkerboard	O
pattern	O
plot	O
can	O
be	O
obtained	O
in	O
10	O
seconds	O
,	O
far	O
faster	O
than	O
when	O
time-domain	O
averaging	O
is	O
used	O
to	O
record	O
an	O
evoked	B-Algorithm
potential	I-Algorithm
for	O
each	O
of	O
several	O
check	O
sizes	O
.	O
</s>
<s>
Then	O
the	O
size	O
of	O
the	O
squares	O
was	O
progressively	O
increased	O
so	O
as	O
to	O
give	O
a	O
plot	O
of	O
evoked	B-Algorithm
potential	I-Algorithm
amplitude	B-Application
versus	O
check	O
size	O
(	O
hence	O
"	O
sweep	O
"	O
)	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
running	O
average	O
of	O
the	O
SSEP	O
can	O
be	O
arranged	O
to	O
increase	O
the	O
luminance	O
of	O
a	O
checkerboard	O
stimulus	O
if	O
the	O
amplitude	B-Application
of	O
the	O
SSEP	O
falls	O
below	O
some	O
predetermined	O
value	O
,	O
and	O
to	O
decrease	O
luminance	O
if	O
it	O
rises	O
above	O
this	O
value	O
.	O
</s>
<s>
The	O
amplitude	B-Application
of	O
the	O
SSEP	O
then	O
hovers	O
about	O
this	O
predetermined	O
value	O
.	O
</s>
<s>
Sensory	B-Algorithm
evoked	I-Algorithm
potentials	I-Algorithm
(	O
SEP	O
)	O
are	O
recorded	O
from	O
the	O
central	O
nervous	O
system	O
following	O
stimulation	O
of	O
sense	O
organs	O
,	O
for	O
example	O
,	O
visual	O
evoked	B-Algorithm
potentials	I-Algorithm
elicited	O
by	O
a	O
flashing	O
light	O
or	O
changing	O
pattern	O
on	O
a	O
monitor	O
,	O
auditory	O
evoked	B-Algorithm
potentials	I-Algorithm
by	O
a	O
click	O
or	O
tone	O
stimulus	O
presented	O
through	O
earphones	O
)	O
,	O
or	O
tactile	O
or	O
somatosensory	B-Algorithm
evoked	I-Algorithm
potential	I-Algorithm
(	O
SSEP	O
)	O
elicited	O
by	O
tactile	O
or	O
electrical	O
stimulation	O
of	O
a	O
sensory	O
or	O
mixed	O
nerve	O
in	O
the	O
periphery	O
.	O
</s>
<s>
Sensory	B-Algorithm
evoked	I-Algorithm
potentials	I-Algorithm
have	O
been	O
widely	O
used	O
in	O
clinical	O
diagnostic	O
medicine	O
since	O
the	O
1970s	O
,	O
and	O
also	O
in	O
intraoperative	O
neurophysiology	O
monitoring	O
(	O
IONM	O
)	O
,	O
also	O
known	O
as	O
surgical	O
neurophysiology	O
.	O
</s>
<s>
There	O
are	O
three	O
kinds	O
of	O
evoked	B-Algorithm
potentials	I-Algorithm
in	O
widespread	O
clinical	O
use	O
:	O
auditory	O
evoked	B-Algorithm
potentials	I-Algorithm
,	O
usually	O
recorded	O
from	O
the	O
scalp	O
but	O
originating	O
at	O
brainstem	O
level	O
;	O
visual	O
evoked	B-Algorithm
potentials	I-Algorithm
,	O
and	O
somatosensory	B-Algorithm
evoked	I-Algorithm
potentials	I-Algorithm
,	O
which	O
are	O
elicited	O
by	O
electrical	O
stimulation	O
of	O
peripheral	O
nerve	O
.	O
</s>
<s>
VEP	O
and	O
BAEP	B-Algorithm
can	O
supplement	O
neuroimaging	B-Algorithm
as	O
part	O
of	O
workups	O
to	O
diagnose	O
diseases	O
such	O
as	O
multiple	O
sclerosis	O
.	O
</s>
<s>
Short	O
latency	O
EPs	O
such	O
as	O
SSEP	O
,	O
VEP	O
,	O
and	O
BAEP	B-Algorithm
can	O
be	O
used	O
to	O
indicate	O
prognosis	O
for	O
traumatic	O
and	O
anoxic	O
brain	O
injury	O
.	O
</s>
<s>
Long	O
and	O
Allen	O
were	O
the	O
first	O
investigators	O
to	O
report	O
the	O
abnormal	O
brainstem	B-Algorithm
auditory	I-Algorithm
evoked	I-Algorithm
potentials	I-Algorithm
(	O
BAEPs	B-Algorithm
)	O
in	O
an	O
alcoholic	O
woman	O
who	O
recovered	O
from	O
acquired	O
central	O
hypoventilation	O
syndrome	O
.	O
</s>
<s>
including	O
retina	O
,	O
optic	B-Application
nerve	I-Application
,	O
optic	O
chiasm	O
,	O
optic	O
radiations	O
,	O
and	O
occipital	O
cortex	O
.	O
</s>
<s>
VEP	O
may	O
be	O
abnormal	O
in	O
optic	O
neuritis	O
,	O
optic	O
neuropathy	O
,	O
demyelinating	O
disease	O
,	O
multiple	O
sclerosis	O
,	O
Friedreich	O
’s	O
ataxia	O
,	O
vitamin	O
B12	O
deficiency	O
,	O
neurosyphilis	O
,	O
migraine	O
,	O
ischemic	O
disease	O
,	O
tumor	O
compressing	O
the	O
optic	B-Application
nerve	I-Application
,	O
ocular	O
hypertension	O
,	O
glaucoma	O
,	O
diabetes	O
,	O
toxic	O
amblyopia	O
,	O
aluminum	O
neurotoxicity	O
,	O
manganese	O
intoxication	O
,	O
retrobulbar	O
neuritis	O
,	O
and	O
brain	O
injury	O
.	O
</s>
<s>
In	O
1934	O
,	O
Adrian	O
and	O
Matthew	O
noticed	O
potential	O
changes	O
of	O
the	O
occipital	O
EEG	B-Application
can	O
be	O
observed	O
under	O
stimulation	O
of	O
light	O
.	O
</s>
<s>
Ciganek	O
developed	O
the	O
first	O
nomenclature	O
for	O
occipital	O
EEG	B-Application
components	O
in	O
1961	O
.	O
</s>
<s>
During	O
that	O
same	O
year	O
,	O
Hirsch	O
and	O
colleagues	O
recorded	O
a	O
visual	O
evoked	B-Algorithm
potential	I-Algorithm
(	O
VEP	O
)	O
on	O
the	O
occipital	O
lobe	O
(	O
externally	O
and	O
internally	O
)	O
,	O
and	O
they	O
discovered	O
amplitudes	B-Application
recorded	O
along	O
the	O
calcarine	O
fissure	O
were	O
the	O
largest	O
.	O
</s>
<s>
The	O
average	O
amplitude	B-Application
for	O
VEP	O
waves	O
usually	O
falls	O
between	O
5	O
and	O
20	O
microvolts	O
.	O
</s>
<s>
Normal	O
values	O
are	O
depending	O
on	O
used	O
stimulation	O
hardware	O
(	O
flash	O
stimulus	O
vs.	O
cathode	B-Device
ray	I-Device
tube	I-Device
or	O
liquid	B-Device
crystal	I-Device
display	I-Device
,	O
checkerboard	O
field	O
size	O
,	O
etc	O
.	O
</s>
<s>
Auditory	O
evoked	B-Algorithm
potentials	I-Algorithm
(	O
AEP	O
)	O
can	O
be	O
used	O
to	O
trace	O
the	O
signal	O
generated	O
by	O
a	O
sound	O
through	O
the	O
ascending	O
auditory	O
pathway	O
.	O
</s>
<s>
The	O
evoked	B-Algorithm
potential	I-Algorithm
is	O
generated	O
in	O
the	O
cochlea	O
,	O
goes	O
through	O
the	O
cochlear	O
nerve	O
,	O
through	O
the	O
cochlear	O
nucleus	O
,	O
superior	O
olivary	O
complex	O
,	O
lateral	O
lemniscus	O
,	O
to	O
the	O
inferior	O
colliculus	O
in	O
the	O
midbrain	O
,	O
on	O
to	O
the	O
medial	O
geniculate	O
body	O
,	O
and	O
finally	O
to	O
the	O
cortex	O
.	O
</s>
<s>
Auditory	O
evoked	B-Algorithm
potentials	I-Algorithm
(	O
AEPs	O
)	O
are	O
a	O
subclass	O
of	O
event-related	B-Algorithm
potentials	I-Algorithm
(	O
ERPs	O
)	O
.	O
</s>
<s>
Brainstem	B-Algorithm
auditory	I-Algorithm
evoked	I-Algorithm
potentials	I-Algorithm
are	O
small	O
AEPs	O
that	O
are	O
recorded	O
in	O
response	O
to	O
an	O
auditory	O
stimulus	O
from	O
electrodes	O
placed	O
on	O
the	O
scalp	O
.	O
</s>
<s>
Somatosensory	B-Algorithm
evoked	I-Algorithm
potentials	I-Algorithm
(	O
SSEPs	O
)	O
are	O
EP	O
recorded	O
from	O
the	O
brain	O
or	O
spinal	O
cord	O
when	O
stimulating	O
peripheral	O
nerve	O
repeatedly	O
.	O
</s>
<s>
Because	O
of	O
the	O
low	O
amplitude	B-Application
of	O
the	O
signal	O
once	O
it	O
reaches	O
the	O
patient	O
's	O
scalp	O
and	O
the	O
relatively	O
high	O
amount	O
of	O
electrical	O
noise	O
caused	O
by	O
background	O
EEG	B-Application
,	O
scalp	O
muscle	O
EMG	O
or	O
electrical	O
devices	O
in	O
the	O
room	O
,	O
the	O
signal	O
must	O
be	O
averaged	O
.	O
</s>
<s>
Typically	O
,	O
in	O
the	O
operating	O
room	O
,	O
over	O
100	O
and	O
up	O
to	O
1,000	O
averages	O
must	O
be	O
used	O
to	O
adequately	O
resolve	O
the	O
evoked	B-Algorithm
potential	I-Algorithm
.	O
</s>
<s>
The	O
two	O
most	O
looked	O
at	O
aspects	O
of	O
an	O
SSEP	O
are	O
the	O
amplitude	B-Application
and	O
latency	O
of	O
the	O
peaks	O
.	O
</s>
<s>
When	O
used	O
in	O
intraoperative	O
monitoring	O
,	O
the	O
latency	O
and	O
amplitude	B-Application
of	O
the	O
peak	O
relative	O
to	O
the	O
patient	O
's	O
post-intubation	O
baseline	O
is	O
a	O
crucial	O
piece	O
of	O
information	O
.	O
</s>
<s>
Dramatic	O
increases	O
in	O
latency	O
or	O
decreases	O
in	O
amplitude	B-Application
are	O
indicators	O
of	O
neurological	O
dysfunction	O
.	O
</s>
<s>
During	O
surgery	O
,	O
the	O
large	O
amounts	O
of	O
anesthetic	O
gases	O
used	O
can	O
affect	O
the	O
amplitude	B-Application
and	O
latencies	O
of	O
SSEPs	O
.	O
</s>
<s>
Any	O
of	O
the	O
halogenated	O
agents	O
or	O
nitrous	O
oxide	O
will	O
increase	O
latencies	O
and	O
decrease	O
amplitudes	B-Application
of	O
responses	O
,	O
sometimes	O
to	O
the	O
point	O
where	O
a	O
response	O
can	O
no	O
longer	O
be	O
detected	O
.	O
</s>
<s>
In	O
patients	O
with	O
MS	O
,	O
evoked	B-Algorithm
potential	I-Algorithm
findings	O
often	O
complement	O
findings	O
on	O
MRI	O
.	O
</s>
<s>
SEPs	O
can	O
be	O
helpful	O
to	O
evaluate	O
subcortical	O
and	O
cortical	O
function	O
in	O
comatose	O
patients	O
and	O
are	O
less	O
sensitive	O
to	O
sedative	O
drugs	O
than	O
EEG	B-Application
.	O
</s>
<s>
As	O
in	O
the	O
adult	O
,	O
SEP	O
findings	O
in	O
combination	O
with	O
the	O
clinical	O
assessment	O
and	O
EEG	B-Application
findings	O
can	O
contribute	O
to	O
the	O
determination	O
of	O
prognosis	O
in	O
comatose	O
children	O
.	O
</s>
<s>
The	O
part	O
of	O
the	O
somatosensory	O
system	O
that	O
transmits	O
pain	O
and	O
temperature	O
signals	O
is	O
monitored	O
using	O
laser	O
evoked	B-Algorithm
potentials	I-Algorithm
(	O
LEP	O
)	O
.	O
</s>
<s>
Motor	O
evoked	B-Algorithm
potentials	I-Algorithm
(	O
MEP	O
)	O
are	O
recorded	O
from	O
muscles	O
following	O
direct	O
stimulation	O
of	O
exposed	O
motor	O
cortex	O
,	O
or	O
transcranial	O
stimulation	O
of	O
motor	O
cortex	O
,	O
either	O
magnetic	O
or	O
electrical	O
.	O
</s>
<s>
During	O
the	O
1990s	O
,	O
there	O
were	O
attempts	O
to	O
monitor	O
"	O
motor	O
evoked	B-Algorithm
potentials	I-Algorithm
"	O
,	O
including	O
"	O
neurogenic	O
motor	O
evoked	B-Algorithm
potentials	I-Algorithm
"	O
recorded	O
from	O
peripheral	O
nerves	O
,	O
following	O
direct	O
electrical	O
stimulation	O
of	O
the	O
spinal	O
cord	O
.	O
</s>
<s>
Because	O
MEP	O
amplitude	B-Application
is	O
correlated	O
with	O
motor	O
excitability	O
,	O
they	O
offer	O
a	O
quantitative	O
way	O
to	O
test	O
the	O
role	O
of	O
various	O
types	O
of	O
intervention	O
on	O
the	O
motor	O
system	O
(	O
pharmacological	O
,	O
behavioral	O
,	O
lesion	O
,	O
etc	O
.	O
)	O
.	O
</s>
<s>
Somatosensory	B-Algorithm
evoked	I-Algorithm
potentials	I-Algorithm
provide	O
monitoring	O
for	O
the	O
dorsal	O
columns	O
of	O
the	O
spinal	O
cord	O
.	O
</s>
<s>
Sensory	B-Algorithm
evoked	I-Algorithm
potentials	I-Algorithm
may	O
also	O
be	O
used	O
during	O
surgeries	O
which	O
place	O
brain	O
structures	O
at	O
risk	O
.	O
</s>
