Friday, 19 January 2018

MEG Evaluation of the Function of Alpha and Beta Rhythms After Visual Stimulation

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.

No comments:

Post a Comment