Past, Current and Future Clinical Applications of MEG

Abstract

Magnetoencephalography (MEG) is a technique which detects weak magnetic fields from above the surface of the head produced by electrical activity within the brain (Hamalainen et al., 1993). It is non-invasive, acoustically silent and able to measure a direct correlate of neuronal activity with sub-millisecond resolution. The technique is therefore well suited to clinical applications as it can readily be used in children and other populations who may not tolerate more demanding procedures such as fMRI or PET. Clinical applications of MEG, although currently limited, have developed in parallel with advances in hardware, software, analysis tools and general understanding of the technique as a non-invasive measure of biomagnetic neuronal activity. The goal of this review is to describe the advances made to date regarding the clinical applications of the technique and the potential areas for expansion and application in the future. Although much MEG research has been conducted in clinical populations, helping to provide an understanding of the pathology and manifestation of various categories of illness, it generally remains a technique used in the research laboratory rather than as a routine part of clinical evaluations. MEG is routinely used in research to investigate the dynamic neuronal processes involved in the representation of sensory systems such as vision, audition, somatosensation and movement. The technique is also readily applied to experiments studying more cognitive processes such as language perception, memory encoding and retrieval and higher level tasks. Non-invasive imaging of the human brain is potentially a very useful diagnostic tool in the identification, prevention and treatment of numerous disease and illnesses as it is able to study a range of cerebral functions. The main clinical application of MEG remains in the pre-surgical evaluation of patients suffering from epilepsy. In recent years, the technique has been applied to the study of a much broader range of symptoms and pathologies, however this is almost exclusively in the context of research on clinical populations rather than being a routinely used diagnostic procedure. The aim of this chapter is not to provide an exhaustive review of all studies which report the use of MEG scanning techniques on individuals from a clinical population. The aim is to give an overview of how the clinical applications of the technique have developed in parallel with purely methodological and empirical research applications and to highlight steps which are necessary for the technique to be more readily applied to a wider range of clinically relevant problems. The first part of this chapter gives on overview of the early uses of MEG in the patient care and treatment plan of individuals suffering from epilepsy. Again, rather than focusing on the many studies published in this area which provide evidence for 1