With high frequency filtering, muscle artifact may become distorted and look like?

High-frequency filtering is often utilized in electroencephalography (EEG) to reduce unwanted muscle artifacts that can interfere with the more relevant brain wave patterns. When muscle activity is filtered at high frequencies, it can sometimes take on a form that resembles beta activity, which is characterized by higher frequency waves typically in the range of 12-30 Hz.

Beta activity is often associated with alertness and active thinking, and the presence of muscle artifacts can create distortions in the EEG reading that lead to what appears to be increased beta activity. Muscle contractions, particularly those from facial muscles, can generate high-frequency electrical signals that when filtered may be misinterpreted as brain activity rather than residual muscle influence.

It's important to consider that other options like theta, lambda, and alpha activities are characterized by different frequency ranges and physiological states, which typically do not correlate with the effects of high-frequency muscle artifacts on the EEG signal. Thus, the resemblance to beta activity is a direct consequence of the nature of the filtered signals.