Figure 1: Shows the distortion of EEG activity and epileptiform activity by the inappropriate use of high and low frequency filters (HFF and LFF). a) Common average reference with LFF 1 Hz and HFF 70 Hz. Spikes are seen at T1, F7 and T3. Note the sleep activity in the midline central and frontal regions. b) same spikes with LFF 5 Hz and HFF 15 Hz. Note that the amplitude of the spikes have become smaller, along with loss of sharpness. Sleep activity and the slowing of background during sleep are also less apparent.