neuromagnetism

Neuromagnetism refers to magnetic fields produced by neuronal activity in the brain and nervous system. These fields arise from ionic currents during neural signaling and are strongest from synchronized postsynaptic currents in cortical pyramidal neurons. When many such neurons align in a common orientation, their fields add and become detectable outside the head. Brain-derived magnetic fields are extremely weak, typically femtotesla to picotesla, requiring sensitive sensors and magnetic shielding.

The principal measurement modality is magnetoencephalography (MEG), which uses arrays of superconducting quantum interference devices (SQUIDs) in a magnetically shielded chamber to detect neuromagnetic signals. Newer room-temperature sensors, such as optically pumped magnetometers (OPMs), enable more flexible or wearable configurations. MEG offers millisecond temporal resolution and high sensitivity to tangential sources, but spatial localization depends on solving the inverse problem and is affected by skull conductivity and sensor geometry. EEG is commonly used alongside MEG to complement localization.

Neuromagnetism supports functional brain mapping for presurgical planning, epilepsy localization, and cognitive neuroscience studies of perception, attention, language, and memory. It is used to characterize neural oscillations across frequency bands (alpha, beta, gamma) and to track rapid dynamics of brain activity with high temporal fidelity.

Development began in the mid-20th century, with early measurements of brain magnetic fields leading to the establishment of MEG. The term neuromagnetism is used to describe this area, though MEG is the standard measurement technique today. Challenges include accurate source localization and artifact rejection.

Emerging directions include wearable MEG with OPMs, improved source localization methods, and integration with MRI and diffusion imaging to enhance spatial accuracy.