Magnetoencephalography

Magnetoencephalography (MEG) is a noninvasive technique that measures magnetic fields generated by electrical activity in the brain. It maps neural activity with millisecond timing and millimeter-scale spatial resolution.

Magnetometers: Sensors that measure magnetic fields, including fields produced by neural currents. MEG systems use magnetometers to detect the brain’s exceptionally weak magnetic fields.
Electroencephalography: A technique that records voltage fluctuations from electrodes placed on the scalp. EEG detects the same broad class of neural currents, but measures scalp voltage rather than magnetic fields.
Epilepsy surgery: Surgical treatment intended to reduce or eliminate seizures by removing or disconnecting seizure-generating tissue. MEG can help localize epileptic activity when planning surgery for drug-resistant seizures.
Electrocorticography: A method that records electrical activity from electrodes placed directly on the surface of the brain. It provides direct, detailed measurements but requires surgery, unlike noninvasive MEG.
Gradiometer: A device that measures the difference in a field between two or more locations. MEG gradiometers suppress distant interference while retaining signals that vary across the head.
Action potential: A rapid, transient change in a cell’s membrane voltage that propagates along an excitable cell. Action potentials contribute to brain activity, though MEG primarily detects synchronized postsynaptic currents.
Auditory evoked field: A magnetic response measured outside the head after an auditory stimulus. Auditory evoked fields show how precisely MEG can time responses to sound.
Near-infrared spectroscopy: A technique that estimates tissue oxygenation by measuring near-infrared light absorption. It is portable and measures hemodynamic changes, whereas MEG records magnetic fields from neural currents.
Superconducting quantum interference device: A highly sensitive magnetometer that uses superconducting loops and quantum interference. SQUID sensors have traditionally enabled MEG systems to measure femtotesla-scale signals.
Postsynaptic potential: A change in a neuron’s membrane voltage caused by synaptic input from another cell. Synchronized postsynaptic currents are major contributors to the magnetic fields MEG records.

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