Measuring the brain’s intricate activity helps scientists and clinicians understand its functions and disorders. Two prominent non-invasive techniques used for this purpose are Magnetoencephalography (MEG) and Electroencephalography (EEG). These methods provide valuable insights into how our brains process information and respond to various stimuli, playing a significant role in both research and medical diagnosis.
Understanding Brain Activity Measurement
Neurons, the fundamental units of the brain, communicate through electrical signals. When many neurons fire synchronously, these electrical currents generate measurable phenomena. Electroencephalography (EEG) directly detects voltage fluctuations produced by this collective neuronal activity. Small electrodes placed on the head pick up these electrical potential differences, reflecting the summed activity of millions of neurons.
The same electrical currents that produce voltage changes also create faint magnetic fields. Magnetoencephalography (MEG) measures these magnetic fields from the brain. Because these magnetic fields are extremely weak, roughly one billionth the strength of the Earth’s magnetic field, Superconducting QUantum Interference Devices (SQUIDs) are the sensitive detectors used in MEG systems. MEG scans are conducted inside a magnetically shielded room to prevent external magnetic interference from overwhelming these weak brain signals.
Distinguishing MEG and EEG
MEG and EEG primarily differ in the signals they measure and how surrounding tissues affect them. EEG records electrical potentials on the scalp, which are distorted as they pass through surrounding tissues. These tissues distort the electrical signals, complicating their exact origin within the brain.
Magnetic fields, in contrast, pass through tissues unimpeded. This means MEG signals are less distorted than EEG, allowing more precise localization of neural sources. MEG offers superior spatial resolution, particularly for activity from deeper brain structures. Both techniques provide excellent temporal resolution, capturing brain activity changes within milliseconds, faster than other neuroimaging methods.
EEG systems are relatively portable and more affordable, typically costing thousands of dollars. MEG systems are large, stationary installations requiring a dedicated shielded room, often costing millions of dollars.
Applications in Neuroscience
Both MEG and EEG serve important roles in clinical settings and neuroscience research. In clinical practice, they are frequently used to diagnose and manage epilepsy by localizing the seizure onset zone. This localization is often a crucial step in planning surgical interventions to remove affected brain tissue. These techniques also assist in pre-surgical mapping for patients with brain tumors or lesions, helping neurosurgeons identify and preserve functional areas like those responsible for motor control or language. This mapping helps minimize neurological deficits after surgery.
In research, MEG and EEG are tools for studying cognitive processes like perception, memory, and attention. They allow investigation into how brain regions communicate and form networks during tasks. Researchers also use these methods to explore brain activity patterns associated with neurological and psychiatric conditions, such as Parkinson’s disease, depression, or schizophrenia. Often, MEG and EEG are used in combination for a more comprehensive understanding of brain function, leveraging their complementary strengths in spatial and temporal resolution.
What to Expect During a Scan
Undergoing an MEG or EEG scan is non-invasive, involving no injections, needles, or radiation. During an EEG, a technician will place a cap or individual electrodes on your scalp, often with conductive gel for good signal transmission. You will sit or lie comfortably, and the process is quiet and painless.
For an MEG scan, you will lie or sit in a comfortable chair, with your head positioned inside a helmet-like device containing sensors. The procedure takes place within a magnetically shielded room to block environmental magnetic noise. Scans can last from 30 minutes to a few hours, depending on the study or clinical question.