Check Impedance; Check Sedation - TDT Medusa4Z User Manual

Check Impedance

The Medusa4Z includes built-in impedance checking. Impedance is a measure of resistance
from electrode to ground. High impedance can result in lower response signals or no signal at
all. After inserting electrodes, run an impedance check for the subject to verify a good insertion
and working electrodes.
To check the impedance level:
1. Press the button next to the channel indicator (e.g. CHAN-1). The impedance between
channel and ground will be shown on the screen.
2. Press the REF impedance button to test the reference electrode impedance to ground.
Note
The impedance frequency was set in the Medusa4Z Setup options, see
Important
The impedance of the input channel (CHAN-1) and the reference (REF) must match, ideally at 1K - 3K for each.
Tip
If the impedance is very high (> 20K), it is likely that one of the electrodes is not properly connected. If both the
output channel and reference show high impedance, it is likely the ground electrode is not making good contact.

Check Sedation

If the subject is not fully sedated throughout testing, subject responses, such as muscle
movements or distress, can interfere with ABR recordings. To avoid this, always check the
subject before beginning your experiment and monitor the subject for signs of wakefulness
during testing.
Toe Pinch For small lab subjects, a toe pinch is the most effective method to check for full
sedation. Extend the rear leg and use your fingernails to firmly pinch toe or foot webbing. There
should be no recoil. If there is any response, such as leg movement, the subject is not
adequately anesthetized.
Running the Experiment | 28
The Test Equipment.