DC MEG fields during migraine

1 Introduction Recent studies of migraine-with-aura patients involving transmagnetic stimulation and visual stimulation have indicated enhanced excitability of the occipital cortex [1,2]. This hyperexcitability maybe the basis for Spreading Cortical Depression (SCD), which is thought to be the underlying mechanism of migraine-with-aura [3]. SCD and the resulting MEG signals are discussed in reference 4, and 5. The present study investigates the MEG waveforms arising during spontaneous migraine-with-aura and evoked migraine auras in humans, to ascertain whether similar signals suggestive of SCD occur, and to understand the relations between SCD and migraine [4,5,6]. Neuromagnetic fields were measured during visual stimulation of the occipital cortex in eight migraine patients: 3 men, 5 women and in six controls: 1 man, 5 women, with no history of migraine headaches. Migraine patients were classified based on the International Headache Society (IHS) criteria [7]. Five ictal migraine patients were studied during spontaneous migraine with aura. All subjects gave written informed consent. These studies were performed utilizing a 148-channel Neuromagnetometer (4D Neuroimaging WH2500). Migraine patients experiencing a unilateral headache and/or lateralized neurological symptoms at the time of the study were monitored for 15–20 minutes if their symptoms permitted. Migraine subjects not experiencing a headache and controls were monitored for 18 minutes during presentation of a visual stimulus. The stimulus consisted of a circular checkerboard pattern, with 50-degree radius and 5 degree check size that alternated black and white at 8 Hz. The pattern was projected onto an opaque white projection screen and delivered to the subject using a system of mirrors. Each subject was asked to focus on a black dot in the center of the oscillating image on the screen. All data were digitized at 290.64 samples per second, with a band pass of 0-50 Hz. The Neuromagnetic data collected during the passive viewing of circular checker board pattern stimulus were analyzed for DC MEG shifts that occur when neurons are depolarizing in a propagating manner. The alternating checkerboard stimulus has been used to successfully stimulate migraine auras in previous migraine studies [2]. Data were filtered at 0.001-50 Hz to remove any equipment drift which was coherent in all 148 channels. The data were then decimated from 254 to 11 samples per second to simplify computer manipulations. These two steps did not affect the slowly varying DC shifts, which occur over minutes. Data were normalized to compensate for difference in head sizes of the subjects and …