What does a poor common mode rejection ratio result in during an EEG recording?

A poor common mode rejection ratio (CMRR) in an EEG recording can lead to increased electrical noise. The CMRR is a measure of the ability of the EEG equipment to eliminate noise or interference that affects both leads equally, thereby allowing the actual neural signals to be more accurately captured.

When the CMRR is low, the system is less effective at distinguishing the true brain signals from the noise. This results in the amplification of irrelevant electrical noise, which can obscure the actual EEG signals. As a consequence, the quality and clarity of the recording are compromised, making it difficult to interpret brain activity accurately.

In comparison, a high CMRR allows for a cleaner signal by effectively cancelling out noise that is common to both electrodes, thus improving the overall fidelity of the EEG recording.