TDT RZ2, Manual, Page: 326 / 736

7-12 System 3
IZ2/IZ2H Stimulator
+/- 150mV (which is likely to be the case), this will light the LED status light on
an open channel.
Similarly, if you hold one channel to 0 uA (Fill Value set to ‘Zero’ in the Injector
gizmo) and stimulate through another nearby channel, the voltage on the channel
held at 0 uA must rise so that no current flows across the electrode. This will also
light the LED status light on a channel set to 0 uA output.
If the headstage/adapter/electrodes are not in the subject, then the electrical circuit
is incomplete and the impedance that the IZ2 sees on its outputs is very high. This
is enough to raise the output voltage and turn on the LED status lights. This is also
true of electrodes that have very high impedance at DC - even though the IZ2
output noise floor is low, a high enough impedance at DC will cause a non-
negligible DC current on the outputs. Therefore, we recommend enabling the Shunt
resistors to reduce the DC current flow to the subject when attempting to stimulate
through very high impedance electrodes.
Bipolar and Multiple Subject Stimulation
In voltage mode, setting a channel to 0V effectively ties it to ground so it will act
as part of the return path for stimulation. For bipolar stimulation, with the ground
wire connected, open all the unused channels and send the inverse signal through
the return electrode so that a current sources/sink forms at the desired electrodes.
There will still be some leakage current through the ground connection, so if you
want true bipolar stimulation you will have to completely disconnect the ground
connection from the IZ2 and use one of the electrodes as the return ground.
Removing the ground connection also works for stimulating multiple subjects
simultaneously. Send the stim signal through one channel and the inverse signal
through a second channel to act as the return.