AAEM minimonograph #39: digital filtering: basic concepts and application to evoked potentials.

Filtering of evoked potentials has been performed in clinical laboratories using both analog and digital methods. Analog methods introduce distortion caused by nonlinear phase shift which may be quite severe. Digital methods, while avoiding distortion caused by phase shift, reveal evoked potential components which may or may not correspond to distinct singular neuroanatomic generators or homogeneous neuroanatomic systems. Thus, components identified with zero phase shift digital filters at restricted bandpass must be compared with components seen in open bandpass recordings. In some specific circumstances, high-pass filtering of short-latency somatosensory-evoked potentials may distinguish slow asynchronous synaptic activity from fast and synchronous synaptic, lemniscal, or axonal activity.