Editing Magnetoencephalography (section)

== Use in the field ==
[[File:MEG map.png|thumb|371x371px|Over 100 MEG systems are known to operate worldwide, with Japan possessing the greatest number of MEG systems per capita and the United States possessing the greatest overall number of MEG systems. A very small number of systems worldwide are designed for infant and/or fetal recordings.]]
In research, MEG's primary use is the measurement of time courses of activity. MEG can resolve events with a precision of 10 milliseconds or faster, while [[functional magnetic resonance imaging]] (fMRI), which depends on changes in blood flow, can at best resolve events with a precision of several hundred milliseconds.  MEG also accurately pinpoints sources in primary auditory, somatosensory, and motor areas. For creating functional maps of human cortex during more complex cognitive tasks, MEG is most often combined with fMRI, as the methods complement each other. Neuronal (MEG) and [[hemodynamics|hemodynamic]] fMRI data do not necessarily agree, in spite of the tight relationship between local field potentials (LFP) and blood oxygenation level-dependent (BOLD) signals. MEG and BOLD signals may originate from the same source (though the BOLD signals are filtered through the hemodynamic response).

MEG is also being used to better localize responses in the brain. The openness of the MEG setup allows external auditory and visual stimuli to be easily introduced. Some movement by the subject is also possible as long as it does not jar the subject's head. The responses in the brain before, during, and after the introduction of such stimuli/movement can then be mapped with greater spatial resolution than was previously possible with EEG.<ref>{{cite journal | vauthors = Cui R, Cunnington R, Beisteiner R, Deecke L | title = Effects of force-load on cortical activity preceding voluntary finger movement|journal=Neurology, Psychiatry and Brain Research|volume=18|issue=3|year=2012|pages=97–104|doi=10.1016/j.npbr.2012.03.001}}</ref> Psychologists are also taking advantage of MEG neuroimaging to better understand relationships between brain function and behavior. For example, a number of studies have been done comparing the MEG responses of patients with psychological troubles to control patients. There has been great success isolating unique responses in patients with schizophrenia, such as auditory gating deficits to human voices.<ref>{{cite journal | vauthors = Hirano Y, Hirano S, Maekawa T, Obayashi C, Oribe N, Monji A, Kasai K, Kanba S, Onitsuka T | title = Auditory gating deficit to human voices in schizophrenia: a MEG study | journal = Schizophrenia Research | volume = 117 | issue = 1 | pages = 61–7 | date = March 2010 | pmid = 19783406 | doi = 10.1016/j.schres.2009.09.003 | s2cid = 7845180 }}</ref> MEG is also being used to correlate standard psychological responses, such as the emotional dependence of language comprehension.<ref>{{cite journal | vauthors = Ihara A, Wei Q, Matani A, Fujimaki N, Yagura H, Nogai T, Umehara H, Murata T | title = Language comprehension dependent on emotional context: a magnetoencephalography study | journal = Neuroscience Research | volume = 72 | issue = 1 | pages = 50–8 | date = January 2012 | pmid = 22001763 | doi = 10.1016/j.neures.2011.09.011 | s2cid = 836242 }}</ref>

Recent studies have reported successful classification of patients with [[multiple sclerosis]], [[Alzheimer's disease]], [[schizophrenia]], [[Sjögren's syndrome]], [[chronic alcoholism]], [[facial pain]] and [[thalamocortical dysrhythmia]]s. MEG can be used to distinguish these patients from healthy control subjects, suggesting a future role of MEG in diagnostics.<!----><ref name="pmid18057502">{{cite journal | vauthors = Georgopoulos AP, Karageorgiou E, Leuthold AC, Lewis SM, Lynch JK, Alonso AA, Aslam Z, Carpenter AF, Georgopoulos A, Hemmy LS, Koutlas IG, Langheim FJ, McCarten JR, McPherson SE, Pardo JV, Pardo PJ, Parry GJ, Rottunda SJ, Segal BM, Sponheim SR, Stanwyck JJ, Stephane M, Westermeyer JJ | title = Synchronous neural interactions assessed by magnetoencephalography: a functional biomarker for brain disorders | journal = Journal of Neural Engineering | volume = 4 | issue = 4 | pages = 349–55 | date = December 2007 | pmid = 18057502 | doi = 10.1088/1741-2560/4/4/001 | url = http://stacks.iop.org/1741-2560/4/349 | bibcode = 2007JNEng...4..349G | hdl = 10161/12446 | s2cid = 2836220 | hdl-access = free }}</ref><ref name="Montez2009">{{cite journal | vauthors = Montez T, Poil SS, Jones BF, Manshanden I, Verbunt JP, van Dijk BW, Brussaard AB, van Ooyen A, Stam CJ, Scheltens P, Linkenkaer-Hansen K | title = Altered temporal correlations in parietal alpha and prefrontal theta oscillations in early-stage Alzheimer disease | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 106 | issue = 5 | pages = 1614–9 | date = February 2009 | pmid = 19164579 | pmc = 2635782 | doi = 10.1073/pnas.0811699106 | bibcode = 2009PNAS..106.1614M | doi-access = free }}</ref>

A large part of the difficulty and cost of using MEG is the need for manual analysis of the data. Progress has been made in analysis by computer, comparing a patient's scans with those drawn from a large database of normal scans, with the potential to reduce cost greatly.<ref name=rose/>

=== Brain connectivity and neural oscillations ===
Based on its perfect temporal resolution, magnetoencephalography (MEG) is now heavily used to study oscillatory activity in the brain, both in terms of local neural synchrony and cross-area synchronisation. As an example for local neural synchrony, MEG has been used to investigate alpha rhythms in various targeted brain regions, such as in visual<ref>{{cite journal | vauthors = Bagherzadeh Y, Baldauf D, Pantazis D, Desimone R | title = Alpha Synchrony and the Neurofeedback Control of Spatial Attention | journal = Neuron | volume = 105 | issue = 3 | pages = 577–587.e5 | date = February 2020 | pmid = 31812515 | doi = 10.1016/j.neuron.2019.11.001 | hdl-access = free | s2cid = 208614924 | doi-access = free | hdl = 11572/252726 }}</ref><ref>{{cite journal | vauthors = de Vries E, Baldauf D | title = Attentional Weighting in the Face Processing Network: A Magnetic Response Image-guided Magnetoencephalography Study Using Multiple Cyclic Entrainments | journal = Journal of Cognitive Neuroscience | volume = 31 | issue = 10 | pages = 1573–1588 | date = October 2019 | pmid = 31112470 | doi = 10.1162/jocn_a_01428 | hdl-access = free | s2cid = 160012572 | hdl = 11572/252722 }}</ref> or auditory cortex.<ref>{{cite journal | vauthors = de Vries IE, Marinato G, Baldauf D | title = Decoding Object-Based Auditory Attention from Source-Reconstructed MEG Alpha Oscillations | journal = The Journal of Neuroscience | volume = 41 | issue = 41 | pages = 8603–8617 | date = October 2021 | pmid = 34429378 | pmc = 8513695 | doi = 10.1523/JNEUROSCI.0583-21.2021 }}</ref> Other studies have used MEG to study the neural interactions between different brain regions (e.g., between frontal cortex and visual cortex).<ref>{{cite journal | vauthors = Baldauf D, Desimone R | title = Neural mechanisms of object-based attention | journal = Science | volume = 344 | issue = 6182 | pages = 424–427 | date = April 2014 | pmid = 24763592 | doi = 10.1126/science.1247003 | s2cid = 34728448 | doi-access = free | bibcode = 2014Sci...344..424B }}</ref> Magnetoencephalography can also be used to study changes in neural oscillations across different stages of consciousness, such as in sleep.<ref>{{cite journal | vauthors = Brancaccio A, Tabarelli D, Bigica M, Baldauf D | title = Cortical source localization of sleep-stage specific oscillatory activity | journal = Scientific Reports | volume = 10 | issue = 1 | pages = 6976 | date = April 2020 | pmid = 32332806 | pmc = 7181624 | doi = 10.1038/s41598-020-63933-5 | bibcode = 2020NatSR..10.6976B }}</ref>

=== Focal epilepsy ===
The clinical uses of MEG are in detecting and localizing pathological activity in patients with [[epilepsy]], and in localizing [[eloquent cortex]] for surgical planning in patients with [[brain tumor]]s or intractable epilepsy. The goal of epilepsy surgery is to remove the epileptogenic tissue while sparing healthy brain areas.<ref>{{cite book | vauthors = Luders HO| title = Epilepsy Surgery|publisher=New York Raven Press|year=1992}}</ref> Knowing the exact position of essential brain regions (such as the [[primary motor cortex]] and [[primary sensory cortex]], [[visual cortex]], and areas involved in speech production and comprehension) helps to avoid surgically induced neurological deficits. Direct cortical stimulation and somatosensory evoked potentials recorded on [[electrocorticography]] (ECoG) are considered the gold standard for localizing essential brain regions. These procedures can be performed either intraoperatively or from chronically indwelling subdural grid electrodes. Both are invasive.

Noninvasive MEG localizations of the central sulcus obtained from somatosensory evoked magnetic fields show strong agreement with these invasive recordings.<ref>{{cite journal | vauthors = Sutherling WW, Crandall PH, Darcey TM, Becker DP, Levesque MF, Barth DS | title = The magnetic and electric fields agree with intracranial localizations of somatosensory cortex | journal = Neurology | volume = 38 | issue = 11 | pages = 1705–14 | date = November 1988 | pmid = 3185905 | doi = 10.1212/WNL.38.11.1705 | s2cid = 8828767 }}</ref><ref>{{cite journal | vauthors = Rowley HA, Roberts TP | title = Functional localization by magnetoencephalography | journal = Neuroimaging Clinics of North America | volume = 5 | issue = 4 | pages = 695–710 | date = November 1995 | pmid = 8564291 }}</ref><ref>{{cite journal | vauthors = Gallen CC, Hirschkoff EC, Buchanan DS | title = Magnetoencephalography and magnetic source imaging. Capabilities and limitations | journal = Neuroimaging Clinics of North America | volume = 5 | issue = 2 | pages = 227–49 | date = May 1995 | pmid = 7640886 }}</ref> MEG studies assist in clarification of the functional organization of primary somatosensory cortex and to delineate the spatial extent of hand somatosensory cortex by stimulation of the individual digits. This agreement between invasive localization of cortical tissue and MEG recordings shows the effectiveness of MEG analysis and indicates that MEG may substitute invasive procedures in the future.

=== Fetal ===
MEG has been used to study cognitive processes such as [[visual perception|vision]], [[Hearing (sense)|audition]], and [[language processing]] in fetuses and newborns.<ref>{{cite journal | vauthors = Sheridan CJ, Matuz T, Draganova R, Eswaran H, Preissl H | title = Fetal Magnetoencephalography - Achievements and Challenges in the Study of Prenatal and Early Postnatal Brain Responses: A Review | journal = Infant and Child Development | volume = 19 | issue = 1 | pages = 80–93 | year = 2010 | pmid = 20209112 | pmc = 2830651 | doi = 10.1002/icd.657 }}</ref> Only two bespoke MEG systems, designed specifically for fetal recordings, operate worldwide.<ref name="Frohlich_2023">{{cite journal | vauthors = Frohlich J, Bayne T, Crone JS, DallaVecchia A, Kirkeby-Hinrup A, Mediano PA, Moser J, Talar K, Gharabaghi A, Preissl H | title = Not with a "zap" but with a "beep": Measuring the origins of perinatal experience | journal = NeuroImage | volume = 273 | pages = 120057 | date = June 2023 | pmid = 37001834 | doi = 10.1016/j.neuroimage.2023.120057 | s2cid = 257807321 | doi-access = free | url = https://psyarxiv.com/65zsc/download }}</ref> The first was installed at the [[University of Arkansas at Little Rock|University of Arkansas]] in 2000, and the second was installed at the [[University of Tübingen]] in 2008. Both devices are referred to as [[Superconducting QUantum Interference Device|SQUID]] arrays for reproductive assessment (SARA) and utilize a concave sensor array whose shape compliments the abdomen of a pregnant woman. Fetal recordings of cortical activity are feasible with a SARA device from a gestational age of approximately 25 weeks onward until birth. Although built for fetal recordings, SARA systems can also record from infants placed in a cradle head-first toward the sensory array.<ref name="Frohlich_2023" /> A third high density custom-made unit with similar whole abdomen coverage has been installed in 2002 at the University of Kansas Medical Center to assess fetal electrophysiology.<ref>{{Cite web |date=2002-12-10 |title=CTF installs MEG system at KUMC |url=https://www.auntminnie.com/industry-news/article/15563780/ctf-installs-meg-system-at-kumc |access-date=2024-10-22 |website=AuntMinnie |language=en-us}}</ref><ref>{{cite journal | vauthors = Minai U, Gustafson K, Fiorentino R, Jongman A, Sereno J | title = Fetal rhythm-based language discrimination: a biomagnetometry study | journal = NeuroReport | volume = 28 | issue = 10 | pages = 561–564 | date = July 2017 | pmid = 28538518 | pmc = 5611858 | doi = 10.1097/WNR.0000000000000794 }}</ref> While only a small number of devices worldwide are capable of fetal MEG recordings as of 2023, the proliferation of [[Optically pumped atomic magnetometer|optically pumped magnetometers]] for MEG in neuroscience research<ref>{{cite journal | vauthors = Brookes MJ, Leggett J, Rea M, Hill RM, Holmes N, Boto E, Bowtell R | title = Magnetoencephalography with optically pumped magnetometers (OPM-MEG): the next generation of functional neuroimaging | journal = Trends in Neurosciences | volume = 45 | issue = 8 | pages = 621–634 | date = August 2022 | pmid = 35779970 | pmc = 10465236 | doi = 10.1016/j.tins.2022.05.008 | s2cid = 250122240 | doi-access = free }}</ref> will likely result in a greater number of research centers capable of recording and publishing fetal MEG data in the near future.<ref name="Frohlich_2023" />

===Traumatic brain injury===
MEG can be used to identify traumatic brain injury, which is particularly common among soldiers exposed to explosions. Such injuries are not easily diagnosed by other methods, as the symptoms (e.g. sleep disturbances, memory problems) overlap with those from frequent co-comorbidities such as [[post-traumatic stress disorder]] (PTSD).<ref name=rose>{{cite news |title=British army veterans denied treatment for brain injuries | vauthors = Rose D |newspaper=The Observer |date=20 February 2022 |url= https://www.theguardian.com/society/2022/feb/20/british-army-veterans-denied-treatment-for-brain-injuries}}</ref>