Wave of the future.
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Electroencephalography↗
Biomedical subjects
N Tepley
Publications and source records attributed to N Tepley.
Magnetic fields associated with spreading depression in anaesthetised rabbits.
Magnetic fields were measured with SQUID magnetometry outside the skull of anaesthetised rabbits during initiation and propagation of spreading depression (SD) in the cortex. Slowly changing fields (up to 1.4 pT) were observed during the propagation phase, from 4-8.5 min after initiation of SD with KCl application, with maxima at about 6 min. The peak amplitude of the equivalent net dipole generators in the brain was ca. 28 microA.mm, substantially less than previously observed with SD in vitro, but large enough that similar signals might be detectable in man.
Anesthesia, General↗
Auditory evoked cortical magnetic field (M100-M200) measurements in tinnitus and normal groups.
Recently, Hoke et al. (1989) and Pantev et al. (1989) demonstrated that the auditory evoked cortical magnetic field (AECMF) M100 component was larger, and M200 was smaller and occurred later in subjects with unilateral tinnitus compared with normal subjects. These group amplitude differences resulted in an M200/M100 amplitude ratio that was smaller for the subjects with tinnitus. The purposes of the present investigation were to: 1) extend the observations of Hoke et al. (1989), and, 2) determine whether contralateral AECMF differences existed following stimulation of the non-tinnitus and tinnitus ears of patients with tinnitus. Neuromagnetic AECMF recordings were recorded from 25 young normal hearing and 14 patients with unilateral tinnitus and hearing loss. The results failed to support the findings of Hoke et al. (1989). Specifically, there is no evidence suggesting that the M100 amplitude is larger, the M200 latency later, or, the M200/M100 amplitude ratios smaller, when the two samples are compared. Additionally, there were no differences in the amplitudes or latencies of M100 or M200 when results from stimulation of the tinnitus and non-tinnitus ears of tinnitus subjects were compared.
Adult↗
Techniques for DC magnetoencephalography.
DC shifts are known to occur in association with a number of physiologic phenomena including spreading depression, hypoxia, epilepsy, and hypercapnia and possibly in migraine, closed head injury, and ischemia. Magnetoencephalography (MEG) makes it possible to record these shifts by prolonged DC monitoring of brain activity and offers several advantages over DC EEG and DC electrocorticography. Among the advantages of MEG is its non-invasive nature and the lack of impedance changes at the electrode-tissue interface that produce baseline shifts in DC EEG. In DC MEG measurements, great care must be taken in dealing with a variety of artifactual signals. Environmental noise can be reduced by magnetic shielding and recognized by use of reference magnetometers. Patient-generated artifacts are numerous and can be recognized and limited by a variety of methods.
Humans↗
Neuromagnetic fields in migraine: preliminary findings.
Neuromagnetic signals consistent with spreading cortical depression have been observed in 9 of 12 migraine patients studied, but not in normal controls (out of 8 studied) or in patients with non-migrainous headache (4 studied). These signals consist of large amplitude, usually biphasic waveforms presumably arising from the onset or offset of spreading cortical depression in a sulcus, and prolonged attenuation of magnetic amplitudes, associated with suppressed neuronal activity. Techniques are described which recognize various kinds of artefacts and which distinguish changes in state of arousal of the patient from the presumed spreading cortical depression signals.
Cortical Spreading Depression↗
Magnetoencephalographic studies of migraine.
We report for the first time the detection by magnetoencephalography (MEG) of signals observable in migraine patients during headache, but not in controls. These signals consisted of three features: suppression of spontaneous cortical activity, long duration field changes, and large amplitude waves (LAW) of several seconds duration. LAW were also seen during the interictal period. We discuss the possible relationship of these signals to spreading depression (SD), and why the LAW have not been observed in previous studies of SD.
Adolescent↗
The concept of migraine as a state of central neuronal hyperexcitability.
This article explores the hypothesis that migraine with aura is associated with a state of central neuronal hyperexcitability. The authors propose that this central neuronal hyperexcitability involves overactivity of the excitatory amino acids, glutamate, and possibly aspartate. Stimuli that activate the migraine attack evoke neuronal depolarization, slow depolarization shifts, and spreading suppression of spontaneous neuronal activity possible by glutamate and K+ dependent mechanisms. A low brain Mg2+ and consequent reduced gating of glutamatergic receptors may provide the link between the physiologic threshold for a migraine attack and the mechanisms of the attack itself by promoting glutamate hyperactivity, neuronal hyperexcitability, and susceptibility to glutamate-dependent spreading depression.
Adult↗
Neuromagnetism: a new approach for localizing brain function.
The physical origins of neuromagnetic signals are described from which it is concluded that magnetoencephalography is potentially much more applicable than electroencephalography for localizing the sources of a variety of neural activities in the brain. The magnitudes of typical neuromagnetic signals are discussed. Selected examples of MEG studies are given. Recent experiments which appear to indicate directly the association of spreading cortical depression with migraine headache are briefly described.
Brain↗