User manual

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Fig. 4.11.11.2. The best way to measure Rs and PkAmp online. Rs measurement was made from the
capacitative peak transient from the unfiltered trace so as to not attenuate the transient peak (20 KHz
sampling, 10 KHz external filtering). PkAmp measurement was made from filtered trace so as to not
measure the superimposed excess noise (20 KHz sampling, 10 KHz external filtering, 500 Hz internal
filtering). The Rs and Rm measurements were made from the gray 10 KHz unfiltered trace, whereas the
EPSCs would be measured from the blue internal 500 Hz filtered trace.
The second choice, using the Rs Calculation Method radiobuttons in Fig. 4.11.11.1, sets whether you
want to calculate Rs from the peak of the capacitative transient (Figs. 4.11.11.2 and 4.11.11.4D), an
extrapolated peak fitted by a single exponential fit to the capacitative transient, or an extrapolated peak
fitted by a double exponential fit to the capacitative transient.
In order to accurately measure Rs from the Peak of the capacitative transient, the pipette capacitance
must have been cancelled out. WinLTP has a maximum sampling rate of 40 KHz insuring that the
Peak capacitative transient will be captured pretty well (even at 20 KHz). Because the peak of the
capacitative transient is the most trouble-free method, it is the default online method.
Fig. 4.11.11.3 shows double and single exponential fits to capacitative transients in hippocampal
neurons extrapolated back to TimeZero peak to measure Rs. The exponential curve fit is from the
beginning to the end of the Rs/Rm pulse. Note that in these hippocampal neurons, the double
exponential fit gives a ‘good’, ‘correct’ fit with an Rs of ~25 Mohms, whereas the single exponential fit
gives a ‘bad’, ‘incorrect’ fit with an Rs of ~63 Mohms.