Direct comparison
EEG vs MEG: Key Neuroimaging Differences
Compare EEG and MEG across biophysical sources, spatial smearing, sensor tech, and BIDS data standards to choose the right neuroimaging tool.
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How do EEG (Electroencephalography), MEG (Magnetoencephalography) compare side by side?
The table below compares EEG (Electroencephalography), MEG (Magnetoencephalography) across 12 procurement-relevant dimensions, from physical quantity measured through sources.
Side-by-side comparison
| Dimension | EEG (Electroencephalography) | MEG (Magnetoencephalography) |
|---|---|---|
| Physical Quantity Measured | Electric potential differences (voltage, typically 10 to 100 μV) across scalp locations. | Extremely weak magnetic flux densities (typically 50 to 500 fT) emerging outside the head. |
| Primary Neuronal Generators | Extracellular volume currents originating from postsynaptic potentials in cortical pyramidal cells. | Intracellular primary currents flowing along apical dendrites of cortical pyramidal cells. |
| Source Orientation Sensitivity | Sensitive to both radial sources (gyral crowns) and tangential sources (sulcal walls). | Selectively sensitive to tangential sources (sulcal walls); largely blind to radial dipoles. |
| Skull and Tissue Distortion | High spatial smearing and attenuation caused by low skull electrical conductivity (~0.004–0.01 S/m). | Negligible spatial distortion because intervening tissues are magnetically transparent. |
| Temporal Resolution | Sub-millisecond to millisecond-level precision matching rapid neuronal dynamics. | Sub-millisecond to millisecond-level precision matching rapid neuronal dynamics. |
| Spatial Resolution & Localization | Moderate (10–20 mm); requires complex realistic head models (BEM/FEM) to account for volume conduction. | High (2–5 mm for superficial cortical sources); straightforward spherical forward modeling. |
| Sensor Technology & Contact | Electrode arrays (Ag/AgCl) attached directly to the scalp using conductive gel, paste, or dry pins. | Non-contact helmet arrays containing 100–300 SQUIDs (or OPMs) positioned outside the scalp. |
| Facility & Shielding Needs | Operable in standard unshielded or lightly shielded rooms; highly mobile and portable configurations. | Requires a heavily magnetically shielded room (mu-metal/aluminum) and liquid helium cryogenic cooling. |
| Subject Mobility & Tolerance | Tolerates moderate head and body movements; well suited for pediatric, bedside, and ambulatory setups. | Requires rigid head stability within the fixed sensor dewar helmet to prevent motion artifacts. |
| Data Standards (BIDS) | BIDS EEG extension using _eeg.json sidecars, _channels.tsv, and electrode coordinate files (_electrodes.tsv). | BIDS MEG extension using _meg.json sidecars, _channels.tsv (MEGMAG/MEGGRAD), and headshape fiducials. |
| When to Choose | Choose EEG for budget-constrained projects, pediatric or bedside cohorts, mobile paradigms, or radial source detection. | Choose MEG for high-precision cortical source localization, presurgical sulcal spike mapping, or distortion-free frequency dynamics. |
| Sources | BIDS Specification v1.11.2 (EEG); PMC11367220 (electromagnetic head modeling). | BIDS Specification v1.11.2 (MEG); PMC13581884 (epilepsy multimodal neuroimaging); PMC11367220. |
Common questions
Common questions about EEG (Electroencephalography) vs MEG (Magnetoencephalography)
Why is MEG more spatially accurate than EEG?
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MEG achieves higher spatial localization accuracy because biological tissues like the skull and scalp have magnetic permeability virtually equal to empty space, allowing magnetic fields to pass through without blurring. EEG potentials, by contrast, are smeared and distorted by the high electrical resistance of skull bone.
Why is MEG blind to radial brain sources?
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In a spherically symmetric conductor model of the head, a purely radial current dipole produces no magnetic field outside the sphere because the magnetic fields produced by intracellular currents and extracellular volume currents cancel each other out. Only tangential currents produce detectable external magnetic fields.
Can EEG and MEG be used together?
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Yes. Simultaneous EEG and MEG recordings provide complementary coverage: MEG precisely localizes tangential sources in cortical sulci, while EEG captures radial sources on gyral crowns and deep subcortical structures. Both can be integrated into standard BIDS neuroimaging datasets.
Going deeper
