Event-Related Magnetic Fields Associated with Auditory Oddball Paradigm — Postoperative Study in Patients with Temporal Lobe Epilepsy

Abstract

Regarding the late positive component of event-related potentials (ERPs) associated with auditoiy oddball paradigm which is now well known as P300, many studies have been done about its characteristics and neural generators. Since P300 is considered to reflect higher brain functions, some investigators have studied the topographical distribution of the scalp-recorded P300 as well as invasive recording using intracranial depth electrodes or chronically implanted subdural electrodes to identify its neural generators and functional significance [1–4]. In addition, there are several studies using magnetoencephalography (MEG), which has been developed as one of the non-invasive technology, to elucidate the brain functions. Two regions have been suggested regarding the sources of the event-related magnetic fields corresponding to P300; the mesial region of the temporal lobe, possibly the hippocampus [5, 6], and the superficial temporal lobe [7]. Rogers et al. [8] also suggested that the responses to the target stimuli arose in the deep regions of brain initially and were transferred to the auditory cortex. However, since these studies recorded the magnetic responses from the restricted area with one or several channels of magnetometer and analyzed them with one dipole model, it might not be enough to disclose the cognitive processing which activates many regions simultaneously and parallel. Therefore, in order to elucidate the generator sources of P300, it would be better to acquire the responses of all the areas in the brain simultaneously and to analyze them by adopting the multidipole model. We studied the event-related magnetic fields (ERFs) associated with the auditory oddball paradigm in normal volunteers and in patients after the operation for the temporal lobe epilepsy by using a whole head magnetometer with 122-channel planar first-order gradiometers to clarify the possible brain areas involved in the cognitive processing.