Axon Axopatch 200B, Theory Of Operation

Page: 59 / 153

LOW NOISE RECORDING • 43
Chapter 5
Chapter 5
Low Noise Recording Techniques
The PATCH configuration of the Axopatch 200B is capable of producing single-channel
recordings with significantly lower noise than a standard resistive patch clamp because of
the inherently low noise of the integrating headstage, particularly at low to moderate
frequencies (below 10 kHz). Low-noise performance is further improved by active cooling
of the critical circuitry.
To realize this performance the user must pay close attention
to other sources of noise. This is because the total rms noise of a patch clamp recording is
the square root of the sum of the individual squared rms noise sources. This means that
any particular noise source that is large will dominate the total noise and make other noise
sources insignificant. Therefore, all potentially contributing noise sources must be
minimized. Specifically, the headstage, the pipette glass, the holder, and the seal contribute
significantly even under circumstances where extraneous noise pickup from the environ-
ment is negligible. It is absolutely crucial that the entire preparation be properly shielded
and hum from power supply, mains, and other sources be negligible,
i.e. , < 0.1 pA
p-p
.
(Actually, < 0.01 pA
p-p
is possible with some effort). In this section, we suggest some
approaches to low-noise recording of single channels. While these same approaches are a
good idea for whole-cell recording, they are less important there since in whole-cell
recording the dominant noise source comes from the access resistance in series with the
whole-cell capacitance.