Hyperexcitability of the primary somatosensory cortex in migraine—a magnetoencephalographic study

Author： Lang Eberhard Kaltenhäuser Martin Neundörfer Bernhard Seidler Sia

ISSN： 1460-2156

Source： Brain, Vol.127, Iss.11, 2004-11, pp. : 2459-2469

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Abstract

The excitability of the cerebral cortex in the interictal state of migraine appears to be fundamental in the brain's susceptibility to migraine attacks. Subpopulations of cortical neurons are reported to have different physiological response properties to different interstimulus intervals (ISIs) and, hence, may be differentially altered or modulated in migraine. The aim of this study therefore was to evaluate response characteristics of temporally and spatially defined neuronal subpopulations in the cortex of migraineurs. To this end, we measured, by means of magnetoencephalography (37-channel neuromagnetometer), the response properties of the early components of the somatosensory evoked magnetic fields following electrical stimulation of the median nerve, the N20m and P35m, at ISIs ranging between 0.3 and 6 s. As a measure of the number of excited neurons underlying the N20m and P35m, we evaluated the root mean square (r.m.s.) of the deflections across all 37 channels at the corresponding latencies and the corresponding dipole moment of the equivalent current dipole (ECD strength). Twenty consecutive women with at least three migraine attacks/month (range 3–8/month) fulfilling the International Headache Society criteria and 20 age-matched healthy women were included in the study. In migraineurs, the r.m.s. and ECD strength of N20m was increased at all ISIs (r.m.s., P < 0.05;="" ecd="" strength,="">P < 0.01)="" and="" positively="" related="" to="" the="" mean="" attack="" frequency="" (r.m.s.,="">Rs = 0.6, P < 0.01;="" ecd="" strength,="">Rs = 0.5, P < 0.05).="" in="" contrast,="" the="" r.m.s.="" and="" ecd="" strength="" of="" p35m="" did="" not="" differ="" significantly="" between="" migraineurs="" and="" control="" subjects="" and="" did="" not="" correlate="" significantly="" with="" the="" frequency="" of="" migraine="" attacks.="" responses="" to="" different="" isis="" did="" not="" differ="" significantly="" between="" migraineurs="" and="" control="" subjects.="" the="" r.m.s.="" of="" n20m="" was="" stable="" for="" isis="" between="" 0.5="" and="" 6="" s="" and="" decreased="" significantly="" at="" an="" isi="" of="" 0.3="" s.="" in="" contrast,="" the="" r.m.s.="" of="" p35m="" decreased="" continuously="" as="" the="" isi="" was="" decreased="" below="" 6="" s="" and="" this="" reached="" significance="" for="" an="" isi="" of="" ≤1="" s.="" habituation="" of="" n20m="" or="" p35m,="" i.e.="" a="" decrease="" in="" response="" magnitude="" following="" repetitive="" stimulation="" over="" time,="" was="" not="" found="" in="" either="" the="" control="" subjects="" or="" in="" the="" migraineurs.="" it="" is="" concluded="" that="" the="" population="" of="" neurons="" in="" the="" primary="" somatosensory="" cortex="" underlying="" the="" n20m="" are="" hyperexcitable="" and="" that="" this="" hyperexcitability="" is="" linked="" to="" the="" frequency="" of="" migraine="" attacks.="" this="" hyperexcitability="" appears="" not="" to="" be="" related="" to="" habituation="" since="" habituation="" was="" not="" found="" in="" the="" control="" subjects.="" in="" contrast,="" the="" magnitude="" of="" p35m="" is="" not="" pathophysiologically="" linked="" to="" the="" interictal="" state="" of="" migraine.="" furthermore,="" the="" cellular="" mechanisms="" causing="" isi-dependent="" depression="" of="" n20m="" and="" p35m="" are="" not="" altered="" in="" migraine.="">