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Magnetoencephalography (MEG) is an electrophysiologic brain imaging technology that has been applied to the study of mental illness, particularly schizophrenia. Like electroencephalography, it provides excellent temporal resolution, and in combination with magnetic resonance imaging, can also provide good spatial resolution. Studies of the auditory system in schizophrenia using MEG have demonstrated an abnormality in functional cerebral asymmetry, in which persons with schizophrenia typically show reduced, or reversed, cerebral asymmetry compared with normal subjects. This abnormality is sex-specific; it is more pronounced in males with schizophrenia. These findings have not been demonstrated using other neuroimaging strategies. Thus, MEG appears to offer a unique and valuable contribution to psychiatric neuroimaging. Current research and clinical applications of MEG are limited, however, by the high cost of instrumentation. The cost of MEG systems should improve as more applications are developed, in schizophrenia as well as other neuropsychiatric conditions, and hospitals begin to invest in the technology.
Magnetoencephalography (MEG) systems use superconducting electronics and magnetic shielding to detect the magnetic fields generated by synaptic neuronal activity. This chapter focuses on two types of quantitative analyses of human electrophysiological data: spectral analysis methods and evoked potentials. Spectral analysis of Electroencephalography (EEG) and MEG signals across multiple sensor locations reveals clear spatial patterns. EEG and MEG activity can be subdivided into three major subdivisions: spontaneous activity, evoked responses, and induced responses. Evoked responses are time domain averages across multiple trials of a repeating stimulus or response. Electroencephalographic and MEG methods based on time-frequency transformation are usually concerned with capturing changes in the brain's oscillatory phenomena produced by stimuli, mental events, or responses. A valid measure of connectivity between regions of the brain engaged in the same cognitive process or behavior is among the most highly prized uses of EEG and MEG data.
Magnetoencephalography (MEG) provides extremely fine temporal resolution and reasonable spatial resolution within the same recording, which makes it fairly unique among the various imaging strategies. MEG is more comfortable for children than electroencephalography (EEG) since it does not involve scalp abrasion, which is particularly bothersome in studies using high sensor densities. MEG provides high temporal resolution and moderate spatial resolution in a relatively comfortable, nonthreatening environment, characteristics that should make it ideal for use in child psychiatry. This chapter talks about the neurophysiologic and neuroanatomic basis of MEG signals. Instrumentation in MEG has evolved significantly since the early 1980s from single channel neuromagnetometer systems to large, high-density whole-head arrays. The most common data analysis technique in MEG involves signal averaging to improve the signal-to-noise ratios (SNR). The chapter presents the comparison of MEG- and EEG. EEG reflects primarily extracellular current and MEG measures intracellular current.
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