Certain Investigations on an Electroencephalogram (EEG) Montaging and Remontaging
A digital EEG system allows the montage and filter settings to be determined at the time the EEG is reviewed, rather than at the time it is recorded. The EEG is recorded with minimally restrictive analog filter settings and with potentials at all electrodes measured with respect to a single common reference. A computer can then process the data as they are displayed on a screen or printer, reformatting the original referential montage to any desired referential or bipolar montage and digitally filtering the data as needed. Input and output montages are described by matrices and singular value decomposition is used to find the linear transformation. An error signal can be calculated from the input data to monitor remontaging validity. This algorithm also identifies output channels that cannot be obtained from the specified input. If necessary, the same segment of EEG can be displayed repeatedly, using different montages and filters. The Laplacian montage and spatial filtering of EEG using principal component analysis are other potentially useful digital techniques, which may aid the interpretation of EEGs.