Signal Quality and Artifacts

Electrical Noise: 50/60Hz Mains Frequency

Characteristic Electrical Noise

If you notice a very regular, sinusoidal frequency overlaying your graph then you should make every attempt to minimize the electrical noise in your testing area. Electrical appliances may introduce noise into your signal. To limit the amount of electrical noise affecting your recording, check the following: 

1. Main power chord should be plugged directly into a grounded wall outlet. Do not plug the system into a power strip. 
2. The testing room should be away from large electrical systems such as HVAC, refrigerators, elevators, cage cleaners, server rooms, etc. There should be at least one room between the testing room and any large electrical appliances. 
3. If possible, avoid rooms with dimmer switches that frequency cause 100 - 120 Hz line noise. Room lights should be fully on or off; red lights may be used - see details. 
4. System cables should be organized in such a way that USB and power cables do not overlap. 

If you continue to see electrical noise in your signal, try using the line filter. 

Biological Noise: Heart and Breath Artifacts

Example of heartbeat and breath artifacts

Occasionally, heartbeats and respirations may contaminate a response causing deviations in the signal. In the 10-second recording above, 6 obvious breaths can be seen, and innumerable smaller heart beats flutters are present. 

Respirations

Mice breathe at a rate of 160 – 280 breaths per minute.

1. Breath artifacts may occur when the animal's head and eyes move against the electrodes. Be sure that the animal is properly positioned, with their body stretched out. This will ensure that the inflation and deflation of the chest does not affect the signal being recorded. 
2. Animals sedated using gas anesthesia may take very large, gasping breaths. This could indicate that the level of anesthesia is too high. In this case, adjust the intensity of the gas to ease the animal’s breathing.  

 

Heartbeats

A mouse’s heart beats at approximately 550 beats per minute.

1. Heartbeats may arise in a VEP signal if the active VEP needle electrode is placed too far back, near the heart. To avoid this, insert the needle between the ears, facing towards the face of the animal.
2. Diagnosys recommends using 0.3% Hypromellose gel as a conductive solution between the eye and the electrode because it hydrates the eyes while maintaining an electrical connection. Some labs, however, may use saline solution to intermittently wet the eyes. Saline could flow down the animal’s face and neck towards the chest, creating a conductive pathway between the heart and ERG electrode. If you are using saline, please be sure to catch any run-off saline solution with a cotton applicator.