Neurotechnology Research Systems
Stimulator 2.0
- 30 -
5.10
Working with real electrodes
In a typical experimental situation, the properties of the electrode may not be well known and may
vary over time. Characterizing the electrode in saline prior to using it in vivo can provide valuable
information about the condition of the electrode. For example, measuring the impedance of the
electrode before and after implantation can help determine if the electrode was physically damaged
during the implantation process. Likewise estimating the impedance, access resistance, and
capacitance of the electrode periodically can provide clues as to the stability of the electrode tissue
interface over time.
This section shows some measurements obtained from a blunt cut 25 µm diameter platinum
iridium micro-wire electrode in saline. All of the measurements are taken using the same
procedures outlined in the preceding sections that were used with the model electrodes on the test
board. If you have not already done so, practice using the test board before trying to work with
electrodes in saline or trying to work with implanted electrodes.
First measure the impedance of the electrode. With the Vmon scaling set to 40
/mV
pp
, the
resulting voltage monitor output was 7.04 V
pp
implying an impedance of 282 k
:
Next observe the response of the electrode to the default 100 µA 50 µs stimulation pulse.
Current monitor:
50 µs
50 µs
25 µs
7040 mV
pp
@ V
MON
= 282 k
250 mV @ V
MON
= 100 µA @ electrode
250 mV @ V
MON
= 100 µA @ electrode
