A single attenuated channel of EEG may result from:

A single attenuated channel of EEG can indeed result from inter-electrode spacing being too close. When electrodes are positioned too close together, they can pick up signals that are overly similar from adjacent electrodes, causing a form of spatial averaging. This means that the individual contributions from distinct brain regions may not be adequately captured, leading to an attenuated or dampened signal. The electric potential differences that would otherwise be detected by the electrodes may become merged or minimized due to their proximity, ultimately resulting in a less robust EEG channel.

In contrast, placing electrodes too distant from each other may not lead to attenuation, but rather to a lack of sensitivity to localized brain activity. Low input impedance, while it may affect signal quality, does not specifically relate to changes in electrode spacing. Similarly, 60Hz cycle interference, which is often associated with electrical noise, would affect the clarity of the EEG signal but does not inherently cause a single channel to become attenuated purely based on electrode placement.