Magnetoencephalography (MEG)

Magnetoencephalography (MEG) is a functional neuroimaging technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using very sensitive magnetometers.

Principle

MEG is based on the principle that every electrical current generates a magnetic field. When neurons in the brain are active, they produce electrical currents, which in turn generate magnetic fields. These magnetic fields are extremely weak and can be measured using superconducting quantum interference devices (SQUIDs) or other sensitive magnetometers.

Procedure

The MEG procedure typically involves the following steps:

• The patient is seated in a chair or lies on a bed inside a shielded room, which is designed to reduce external magnetic interference.
• A helmet-like device containing the SQUIDs or other magnetometers is placed over the patient's head. This device is usually cooled to very low temperatures using liquid helium to increase its sensitivity.
• The patient is then asked to perform specific tasks, such as reading, listening to sounds, or performing motor activities, while the MEG device records the magnetic fields produced by the brain's electrical activity.
• The recorded data are then analyzed using specialized software to reconstruct the sources of the magnetic fields in the brain and create detailed maps of brain activity.

Applications

MEG has a variety of applications, including:

• Research: MEG is used to study the neural basis of cognitive processes, such as perception, attention, memory, and language processing.
• Clinical diagnosis: MEG can be used to help diagnose and monitor neurological disorders, such as epilepsy, stroke, and brain tumors.
• Neurosurgery: MEG can be used to map the brain's functional areas before surgery, helping surgeons to avoid damaging critical areas during operations.
• Brain-computer interfaces (BCIs): MEG can be used to develop BCIs, which allow people to control devices with their thoughts.

Advantages and Limitations

MEG has several advantages, including:

• High temporal resolution: MEG can record brain activity with millisecond precision, allowing for detailed analysis of neural processes.
• Non-invasive: MEG is a non-invasive technique, which means it does not require any physical contact or insertion of devices into the brain.

However, MEG also has some limitations:

• High cost: MEG systems are expensive and require specialized equipment and expertise.
• Limited spatial resolution: While MEG can provide high temporal resolution, its spatial resolution is limited compared to other neuroimaging techniques, such as functional magnetic resonance imaging (fMRI).