Method and apparatus for producing enhanced EEG or MEG information related to a selected brain activity in a subject. The apparatus includes a two-dimensional array of at least about 16 sensors for recording EEG or MEG traces from the subject. Control and test traces recorded before and during an interval in which the brain activity is occurring, respectively, are each decomposed into a series of basis functions which may be analytic components such as temporal frequency components, generated by spectral decomposition of an ensemble average of the recorded traces, or principal components determined by principal component analysis. The control and test traces are then represented as a sum of the products of the individual basis functions times a spatial domain matrix which represents the spatial pattern of amplitudes of that basis function, as measured by the individual sensors in the array. The signals can be extracted by filtering spatially and/or temporally to remove basis function components which are not related to the selected brain activity (clutter), and to remove spatial frequencies inherent in the spatial domain matrices to optimize the contrast between control and and corresponding test matrices, for each selected basis function.
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