ABSTRACT
This chapter discusses the classical brain source localization techniques. By term classical, we mean the techniques developed initially to localize the brain sources, which include minimum norm estimation (MNE) and a class of low-resolution techniques (such as low-resolution brain electromagnetic tomography [LORETA], standardized LORETA [sLORETA], exact LORETA [eLORETA]), and focal underdetermined system solution (FOCUSS), respectively. First of all, generalized linear model (GLM) is defined for the source localization problem. After which, the mentioned techniques are elaborated in detail with proper aid of mathematical derivations associated with them. It can be observed that LORETA is an advanced version of MNE. Furthermore, the sLORETA and eLORETA are advanced versions of LORETA with different treatment of various parameters within their implementation to generate the solution with less localization error and more accuracy. The FOCUSS technique is considered to belong to the same classical group as it employs weighted minimum norm for the source estimation. It is iterative in nature and hence, has high-computational time for localizing the active sources.
