Topographic maps of brain electrical activity--pitfalls and precautions.

Topographic mapping of brain electrical activity is a popular, powerful, and potentially misleading technique. The map lies at the end of a long chain of physiological, technical, electronic, and mathematical processes and is vulnerable to artifact, error, and distortion at many points. Close attention must be paid to data collection parameters, subject cooperation, minimization of artifact, limitations of resolutions, selection, and transformation of parameters for display, and map generation strategy to yield an accurate, physiologically interpretable map. Review of the data at each step of analysis, from the paper electroencephalogram (EEG) to sets of maps on video display, may be necessary for optimum understanding. Development of more sophisticated qualitative and quantitative concepts of "normal" physiology is needed. These improvements in electrophysiological data analysis demand, rather than obviate, sophistication on the part of the user.