What should the input impedance of an EEG instrument be?

The input impedance of an EEG instrument should be very high to ensure accurate and reliable measurements of the brain's electrical activity. The reason for this requirement lies in the nature of EEG signals, which are extremely weak, typically in the range of microvolts. A very high input impedance minimizes the loading effect on the electrodes, allowing them to capture the subtle electrical signals produced by neuronal activity without significantly altering them.

If the input impedance were low, it would draw more current away from the electrodes, potentially distorting the signals being measured, leading to inaccuracies in the EEG recordings. This is particularly critical since EEG recordings can be affected by various forms of electrical noise, and preserving the integrity of the signal is essential for effective analysis and interpretation.

Having a very high input impedance also helps in reducing the influence of external noise and interference, making it easier to distinguish true brain activity from artifacts. In summary, a very high input impedance is crucial for optimal EEG functionality and accuracy, enhancing the instrument's ability to reflect genuine neural activity.