Editing Magnetoencephalography (section)

==Comparison with related techniques==
MEG has been in development since the 1960s but has been greatly aided by recent advances in computing algorithms and hardware, and promises improved [[spatial resolution]] coupled with extremely high [[temporal resolution]] (better than 1 [[millisecond|ms]]). 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 [[fMRI]].  Its strengths consist in independence of head geometry compared to EEG (unless [[ferromagnetic]] [[implant (medicine)|implants]] are present), non-invasiveness, use of no ionizing radiation, as opposed to PET and high temporal resolution as opposed to fMRI.

=== MEG in comparison to EEG ===
Although EEG and MEG signals originate from the same neurophysiological processes, there are important differences.<ref>{{cite journal | vauthors = Cohen D, Cuffin BN | title = Demonstration of useful differences between magnetoencephalogram and electroencephalogram | journal = Electroencephalography and Clinical Neurophysiology | volume = 56 | issue = 1 | pages = 38–51 | date = July 1983 | pmid = 6190632 | doi = 10.1016/0013-4694(83)90005-6 }}</ref> Magnetic fields are less distorted than electric fields by the skull and scalp, which results in a better spatial resolution of the MEG. Whereas scalp EEG is sensitive to both tangential and radial components of a current source in a spherical volume conductor, MEG detects only its tangential components. Scalp EEG can, therefore, detect activity both in the sulci and at the top of the cortical gyri, whereas MEG is most sensitive to activity originating in sulci. EEG is, therefore, sensitive to activity in more brain areas, but activity that is visible in MEG can also be localized with more accuracy.

Scalp EEG is sensitive to extracellular volume currents produced by postsynaptic potentials. MEG detects intracellular currents associated primarily with these synaptic potentials because the field components generated by volume currents tend to cancel out in a spherical volume conductor.<ref>{{cite journal | vauthors = Barth DS, Sutherling W, Beatty J | title = Intracellular currents of interictal penicillin spikes: evidence from neuromagnetic mapping | journal = Brain Research | volume = 368 | issue = 1 | pages = 36–48 | date = March 1986 | pmid = 3955364 | doi = 10.1016/0006-8993(86)91040-1 | s2cid = 3078690 }}</ref> The decay of magnetic fields as a function of distance is more pronounced than for electric fields. Therefore, MEG is more sensitive to superficial cortical activity, which makes it useful for the study of neocortical epilepsy. Finally, MEG is reference-free, while scalp EEG relies on a reference that, when active, makes interpretation of the data difficult.