Guide
to
Electrophysiological
Recording
The
best
way
to
minimize
or
even
eliminate
this
artifact
is
at
the
source,
by
using
small
stimuli,
isolated
stimulators,
placing
a
grounded
shield
between
the
stimulating
electrodes
and
the
microelectrodes,
etc.
Often,
though,
it
is
not
possible
to
reduce
the
artifact
to
manageable
levels.
The
Axoclamp
900A
can
circumvent
the
effects
of
the
stimulus
artifact
by
Blanking.
At
the
moment
the
logic
level
of
the
BLANK
ACTIVATE
1
input
goes
high,
the
value
of
V
m
is
sampled
and
saved.
For
the
duration
of
the
HIGH
signal,
this
saved
value
is
used
instead
of
the
actual
potential.
In
voltage
‐
clamp
modes
the
voltage
‐
clamp
current
during
the
Blanking
period
will
be
held
at
the
level
that
existed
at
the
start
of
the
period.
A
small
deviation
from
the
command
potential
may
develop
during
the
Blanking
period
as
a
result
of
comparing
the
command
to
the
sampled
value
of
V
m
instead
of
the
instantaneous
value
of
V
m
.
This
deviation
will
only
be
seen
when
the
Blanking
period
ends.
Usually
this
deviation
is
preferable
to
the
situation
that
can
occur
if
Blanking
is
not
used.
If
Blanking
is
not
used
the
artifact
picked
up
by
CHANNEL
1
is
treated
by
the
voltage
‐
clamp
circuit
as
an
attempt
by
the
cell
to
change
its
potential.
Therefore,
the
voltage
‐
clamp
circuit
causes
a
current
to
be
passed
into
the
cell
to
clamp
this
presumed
membrane
potential
change.
If
the
stimulus
artifact
is
large,
the
consequent
current
artifact
can
be
large
enough
to
damage
the
cell.
The
width
of
the
Blanking
period
should
be
no
longer
than
the
minimum
width
required
to
cover
the
period
of
the
stimulus
artifact.
It
is
important
not
to
Blank
for
longer
than
necessary
since
during
Blanking
no
updating
of
V
m
is
allowed.
Even
when
Blanking
is
used,
attempts
should
still
be
made
to
minimize
the
artifact
at
the
source.
Current
Measurement
The
current
injected
down
each
microelectrode
is
independently
measured.
The
measurement
is
true.
Thus,
if
the
microelectrode
blocks,
the
measured
current
falls
to
zero
even
though
a
current
command
may
exist.
Two
current
outputs
apply
to
CHANNEL
1
in
discontinuous
modes
(DCC
and
dSEVC),
the
instantaneous
current
and
the
sampled
current.
The
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