Magnetoencephalography (MEG) is a functional neuroimaging
technique for mapping brain activity by recording magnetic
fields produced by electrical brain currents, using very sensitive
magnetometers and it gives improved spatial resolution
with particularly high temporal resolution. Since the MEG signal
is a direct measure of neuronal activity, its temporal resolution
is comparable with that of intracranial electrodes. MEG
complements other brain activity measurement techniques
such as electroencephalography (EEG), positron emission
tomography (PET), and functional magnetic resonance imaging
(FMRI). It is a non-invasive method and uses no ionizing
radiation, as opposed to PET. MEG can resolve events with a
precision of greater than ten milliseconds (msec), while fMRI,
can at best resolve events with a precision of several hundred
milliseconds (msec). MEG is also being used to better localize
responses in the brain.
The responses in the brain before, during,
and after the introduction of stimuli can be mapped with
greater spatial resolution than was formerly potential used
with EEG.
The pineal gland controls the hormone system and at night
it is releasing one important hormone the melatonin in the blood stream and from the blood stream to the brain. Sandyk
reported a case of a patient with multiple sclerosis in whom
visual perception worsened throughout the course of the day
and improved at night. These changes in vision appeared
to correspond to the circadian secretion of melatonin which
is coupled to the circadian temperature rhythms. Ter Huurne
et al investigated whether aberrant modulation of alpha
oscillations contributes to attention problems in Attentiondeficit/hyperactivity
disorder (ADHD) patients with the use
of MEG.
They suggested that aberrant modulations of alpha
oscillations reflect attention problems because of ADHD and
might be related to the neurophysiological substrate of the
disorder. Babiloni et al investigated if simple delayed response
tasks affect latency and amplitude of MEG midline alpha
rhythms (6-12 Hz) in early dementia. They found that the
alpha peak was later in latency in the demented and normal
elderly subjects than in the normal young subjects and it was
stronger in amplitude in the demented patients than in the
normal subjects. Anninos et al in a MEG study discussed
the potential essential role of the pineal gland in the long term
anticonvulsant effects of external artificial magnetic stimulation
because the pineal gland has been shown to be a magnetosensitive
organ which forms part of a combined compasssolar
clock system and exerts an inhibitory action on seizure
activity. Sandyk et al based on MEG measurements suggested
that patients with nocturnal epilepsy or those experiencing
exacerbation of seizures premenstrually may benefit
from the administration of agents which block the secretion
or action of melatonin.
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