You are reporting focal low amplitude across the frequencies for a specific region. The EEG can be seen with areas of decreased amplitude, not just a beta deficit, but an area of general amplitude minima. This phenomenon is seen well in topographic EEG mapping and has been reported in areas of cortical dysfunction (Brownback and Mason, 1998). The area is effectively shut down and is not functioning. These areas have been observed frontally in attentional and affective disorders (Gunkelman, 1997). The functional areas you describe would suggest hyperactive/impulsive behavior (fight frontal) with poor social environment awareness (right temporal)... is this seen clinically... if not, the effect is likely an artifact. You are right about the subdural doing this attenuation pattern... a chronic subdural attenuates the EEG... but a tumor would generally show as a slow focus in addition to this attenuation. Jay