Concordance between interictal MEG and stereo-EEG predicts seizure freedom after epilepsy surgery.

Abstract

This scientific commentary refers to ‘Correlating magnetoencephalography to stereo-electroencephalography in patients undergoing epilepsy surgery’, by Murakami et al. (doi:10.1093/brain/aww215) . The potential of magnetoencephalography (MEG)—the ability to measure cerebral activity via the brain’s magnetic fields—was recognized in the early decades after Hans Berger developed the first electroencephalography (EEG) device (Berger, 1929). The technical progress necessary to measure the weak cerebral magnetic fields, however, was not achieved until the 1960s. In 1968, using a single induction-coil magnetometer made with two million turns of copper wire, the magnetic field created by the posterior ‘alpha’ rhythm described by Berger decades earlier was finally recorded (Cohen, 1968). The next 20 years saw significant technical improvements in MEG; however, practical clinical applications of the technique were slow to materialize. In this issue of Brain , Murakami and co-workers provide evidence to support the role of MEG in the presurgical evaluation of patients with epilepsy (Murakami et al. , 2016). Epileptogenic source localization using MEG was first described in 1987 (Rose et al. , 1987) in a study comparing EEG, MEG, and electrocorticography (ECoG) localization of epileptogenic tissue. The MEG 3D equivalent current dipoles were calculated and found to be well correlated with the discharges identified on ECoG and via depth electrode placement. Magnetic source imaging (MSI), the combination of MEG and anatomical imaging modalities, began to show particular promise in the 1990s with the development of dual magnetometer and subsequent whole-head sensor array systems, allowing more efficient and detailed bi-hemispheric recordings. An initial report of …