History of EEG
Electroencephalography Devices or EEG was discovered in 1929 by German psychiatrist and neurologist Hans Berger. Berger was the first person who successfully produced recordings of bioelectrical signals from a human brain using scalp electrodes. Initially, Berger faced skepticism from the scientific community regarding his discovery. However, his work laid the foundation for the development of EEG as a clinical tool. The first commercial EEG machine became available in the late 1930s. Since then, EEG has become a widely used diagnostic method in neurology and has helped improve our understanding of brain function.
How EEG Works
An Electroencephalography Devices detects and records the electrical signals produced by the firing of neurons within the brain. Nerve cells communicate via electrical and chemical signals. When a group of neurons fire together, tiny electric currents are produced. EEG devices use electrodes placed along the scalp to detect these currents. The electrodes are attached to thin wires that are connected to an EEG machine. The machine amplifies the brain's electrical activity and converts it into line tracings that can be examined by a neurophysiologist or neurologist.
EEG uses the differences in electric potentials between electrodes to localize the anatomical origin of the neural signals. The most widely used montage is the international 10-20 system where the electrodes are placed at standardized locations along the scalp. EEG provides excellent temporal resolution, with the precision to detect millisecond-scale changes in electrical activity. However, the spatial resolution is relatively poor compared to other neuroimaging techniques like MRI due to distortions introduced by scalp and skull.
Clinical Applications of EEG
Some common clinical uses of EEG include:
- Diagnosing epilepsy - EEG is very effective at detecting seizure activity and helping classify epileptic syndromes. It can detect interictal epileptiform discharges between seizures and ictal activity during seizures.
- Identifying brain tumors - Certain tumors, injuries, or malformations can alter normal EEG patterns. This helps localize lesions.
- Assessing coma and altered mental states - EEG findings are correlated with prognosis and extent of brain injury in comatose patients. It can differentiate between medical comas, medications effects, and neurological damage.
- Monitoring during surgery - Intraoperative EEG is used for functional mapping and to observe neural responses during procedures like tumor resection.
- Sleep studies - Polysomnographic EEG records brain waves together with other physiological signals during sleep. This aids diagnosis of sleep disorders.
- Dementia evaluation - Serial EEGs combined with clinical evaluations can support diagnosis and monitoring of dementias like Alzheimer's.
- Traumatic brain injury - EEG is helpful for assessing injury severity, prognosis, and monitoring post-injury complications like seizures.
Advances in EEG Technology
Modern digital EEG systems provide improved signal quality and analysis capabilities compared to older analog machines. Advances like high density EEG using more electrodes allow recording at higher spatial resolution. New analysis methods like connectivity analysis can study functional correlations between different brain regions. Other promising areas include wireless portable EEG devices, brain-computer interface systems, and combined EEG-fMRI to correlate brain activity with anatomy. Dry EEG electrodes not requiring gel are being developed for improved patient comfort and usability outside clinical settings. Ongoing research aims to expand clinical applications of EEG technology.
EEG provides a direct recording of brain electrical activity with excellent temporal resolution. Since its discovery 90 years ago, it has become an invaluable neurodiagnostic tool. Constant technological advances are helping realize the full potential of EEG to advance our understanding of brain health and disorders. As a noninvasive and portable technique, EEG will likely continue to play a key role alongside other neuroimaging modalities well into the future.
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