Strategy for Objective Comparisons of Inverse Solutions

Abstract

There is much discussion in the Biomagnetism Community about the differences in and usefulness of ‘dipole solutions* and ‘minimum norm solutions’. By ‘dipole solutions’ we mean the wide variety of procedures that assume the current in the brain is well modeled by a small number of current dipoles, and determine the locations and moment vectors of those dipoles. By ‘minimum norm solutions’ we mean the equally diverse group of procedures that do not assume the source is dipolar, and instead minimize the norm of the current, |J|, or a weighted version of the current. We do not wish to discuss the validity of the assumptions made in order to obtain a dipole or minimum norm Solution. Our goal is a quantitative measure for comparing dipole solutions to minimum norm solutions when the true current source is known. We hope that such an objective measure will lead to a more fruitful discussion of the usefulness of dipole solutions and minimum norm solutions, although we acknowledge it will not add anything to the discussion about the validity of the assumptions used to obtain the solutions.