What it looks like
Very fast, spiky, irregular activity, strongest at temporal and frontal electrodes over temporalis and frontalis. It grows with clenching, chewing and tension, and fades with relaxation and sleep. 11
What it means at the bedside
A lower high-frequency filter (for example 35 Hz, or 15 Hz) makes EMG look like beta or even spikes. Reduce the muscle activity at source; use the filter only to see past it, never to diagnose. Try the low-pass control in the viewer on this trace.