<s>
Spike	B-Algorithm
sorting	I-Algorithm
is	O
a	O
class	O
of	O
techniques	O
used	O
in	O
the	O
analysis	O
of	O
electrophysiological	B-Application
data	O
.	O
</s>
<s>
Spike	B-Algorithm
sorting	I-Algorithm
algorithms	O
use	O
the	O
shape(s )	O
of	O
waveforms	O
collected	O
with	O
one	O
or	O
more	O
electrodes	O
in	O
the	O
brain	O
to	O
distinguish	O
the	O
activity	O
of	O
one	O
or	O
more	O
neurons	O
from	O
background	O
electrical	O
noise	O
.	O
</s>
<s>
Neurons	O
produce	O
action	B-Algorithm
potentials	I-Algorithm
that	O
are	O
referred	O
to	O
as	O
'	O
spikes	B-Algorithm
 '	O
in	O
laboratory	O
jargon	O
.	O
</s>
<s>
Frequently	O
this	O
term	O
is	O
used	O
for	O
electrical	O
signals	O
recorded	O
in	O
the	O
vicinity	O
of	O
individual	O
neurons	O
with	O
a	O
microelectrode	O
(	O
exception	O
:	O
'	O
spikes	B-Algorithm
 '	O
in	O
EEG	B-Application
recordings	O
)	O
.	O
</s>
<s>
In	O
these	O
recordings	O
action	B-Algorithm
potentials	I-Algorithm
appear	O
as	O
sharp	O
spikes	B-Algorithm
(	O
deviations	O
from	O
the	O
baseline	O
)	O
.	O
</s>
<s>
This	O
includes	O
the	O
component	O
due	O
to	O
the	O
synaptic	O
currents	O
and	O
the	O
action	B-Algorithm
potentials	I-Algorithm
.	O
</s>
<s>
The	O
synaptic	O
currents	O
have	O
slower	O
time	O
course	O
and	O
the	O
spikes	B-Algorithm
have	O
faster	O
time	O
course	O
.	O
</s>
<s>
They	O
are	O
thus	O
easily	O
separated	O
by	O
filtering	O
:	O
highpass	O
for	O
spikes	B-Algorithm
and	O
low	O
pass	O
for	O
the	O
synaptic	O
mechanisms	O
.	O
</s>
<s>
The	O
component	O
of	O
the	O
field	O
due	O
to	O
the	O
synaptic	O
mechanism	O
is	O
referred	O
to	O
as	O
the	O
local	B-Algorithm
field	I-Algorithm
potential	I-Algorithm
(	O
LFP	O
)	O
.	O
</s>
<s>
Spike	B-Algorithm
sorting	I-Algorithm
refers	O
to	O
the	O
process	O
of	O
assigning	O
spikes	B-Algorithm
to	O
different	O
neurons	O
.	O
</s>
<s>
The	O
background	O
to	O
this	O
is	O
that	O
the	O
exact	O
time	O
course	O
of	O
a	O
spike	B-Algorithm
event	O
as	O
recorded	O
by	O
the	O
electrode	O
depends	O
on	O
the	O
size	O
and	O
shape	O
of	O
the	O
neuron	O
,	O
the	O
position	O
of	O
the	O
recording	O
electrode	O
relative	O
to	O
the	O
neuron	O
,	O
etc	O
.	O
</s>
<s>
These	O
electrodes	O
,	O
positioned	O
outside	O
of	O
the	O
cells	O
in	O
the	O
tissue	O
,	O
however	O
,	O
often	O
'	O
see	O
 '	O
the	O
spikes	B-Algorithm
generated	O
by	O
several	O
neurons	O
in	O
their	O
vicinity	O
.	O
</s>
<s>
Since	O
the	O
spike	B-Algorithm
shapes	O
are	O
unique	O
and	O
quite	O
reproducible	O
for	O
each	O
neuron	O
they	O
can	O
be	O
used	O
to	O
distinguish	O
spikes	B-Algorithm
produced	O
by	O
different	O
neurons	O
,	O
i.e.	O
</s>
<s>
Technically	O
this	O
is	O
often	O
achieved	O
based	O
on	O
different	O
sizes	O
of	O
the	O
spikes	B-Algorithm
(	O
simple	O
but	O
inaccurate	O
version	O
)	O
or	O
more	O
sophisticated	O
analyses	O
which	O
make	O
use	O
of	O
the	O
entire	O
waveform	O
of	O
the	O
spikes	B-Algorithm
.	O
</s>
<s>
The	O
techniques	O
often	O
use	O
tools	O
such	O
as	O
principal	B-Application
components	I-Application
or	O
wavelet	O
analysis	O
.	O
</s>
<s>
Multiple	O
electrodes	O
record	O
different	O
waveforms	O
for	O
each	O
individual	O
spike	B-Algorithm
elicited	O
by	O
the	O
neurons	O
in	O
the	O
vicinity	O
of	O
the	O
electrodes	O
.	O
</s>
<s>
The	O
geometric	O
configuration	O
of	O
the	O
electrodes	O
can	O
then	O
be	O
used	O
to	O
define	O
additional	O
dimensions	O
to	O
analyze	O
which	O
spikes	B-Algorithm
originated	O
from	O
which	O
individual	O
cell	O
in	O
the	O
recorded	O
population	O
of	O
cells	O
.	O
</s>
<s>
Thus	O
the	O
spike	B-Algorithm
sorting	I-Algorithm
using	O
multiple	O
electrodes	O
is	O
better	O
than	O
sorting	B-Algorithm
based	O
simply	O
on	O
waveform	O
shape	O
.	O
</s>
<s>
Spike	B-Algorithm
shapes	O
colored	O
according	O
to	O
their	O
assignment	O
to	O
different	O
neurons	O
.	O
</s>
