Magnetoencephalography in Landau-Kleffner syndrome.

Magnetoencephalography (MEG) detects weak magnetic fields outside the head. Spikes generated on the perisylvian convexity are detected only by electroencephalography (EEG), whereas spikes with intrasylvian generators are selectively seen by MEG. Generators of MEG and EEG spikes are determined using equivalent current dipoles (ECDs) that represent local cortical activity in parallel pyramidal neurons. MEG localizes cortical spike generators with a 1-2-cm spatial accuracy, and with a millisecond time resolution. This allows tracking of neural activity over successive synaptic connections in the cortical network. Both EEG and MEG are necessary for comprehensive spatial and temporal description of perisylvian epileptic networks in the Landau-Kleffner syndrome (LKS). MEG studies suggest that in more than 80% of LKS patients, the bilateral epileptic discharges are generated in the auditory- and language-related perisylvian cortex. Approximately 20% of children with LKS children have a unilateral perisylvian pacemaker that triggers secondary bilateral synchrony of spikes. This 20% may regain considerable language skills after multiple subpial transections (MSTs) of the pacemaker area. Outcome data of a few surgery patients suggest an indispensable role of MEG when planning the most efficient therapy for patients with LKS.