Context: EEG, or electroencephalography, measures brain electrical activity and celebrates its 100th anniversary. Invented by Hans Berger in 1924, EEG captures neuron activity via scalp electrodes, essential for diagnosing epilepsy and assessing brain states like sleep or coma.
Though limited by volume conduction and surface bias, it remains cost-effective, non-invasive, and useful in clinical and research settings, especially when combined with other technologies like MRI.
Introduction to EEG
- EEG (Electroencephalography): A diagnostic test used to detect electrical activity in the brain. It records the brain’s spontaneous electrical activity over a period of time using multiple electrodes placed on the scalp.
- Historical Background: The first human EEG was produced by Hans Berger in 1924, marking the centenary of its invention.
Invention and Development:
- Pioneering Studies:
- Richard Caton (1875): Discovered electrical activity in the brains of animals.
- Adolf Beck (1890): Found fluctuating brain activity in response to sensory stimulation in dogs and rabbits.
- Vladimir Pravdich-Neminsky (1912): Created the first mammalian EEG on a dog’s brain.
- Hans Berger (1924): Produced the first human EEG, named it, and demonstrated its clinical utility.
Working Principle
- Mechanism: EEG measures voltage fluctuations resulting from ionic current within the neurons of the brain.
- Neurons communicate by exchanging ions, generating electrical activity.
- Electrodes: Small, flat metal discs attached to the scalp that detect this activity.
- Recording: The detected signals are amplified and recorded on a computer as wavy lines.
Clinical Applications:
- Diagnosis:
- Epilepsy: Primary diagnostic tool for epilepsy.
- Anesthesia Effects: Monitors brain activity during surgery.
- Sleep Disorders: Evaluates sleep patterns and disorders.
- Coma and Brain Death: Assesses neurological function in coma patients and confirms brain death.
- Research Uses:
- Neuroscience: Studies brain function and cognition.
- Cognitive Psychology and Neurolinguistics: Investigates brain processes related to language and cognition.
- Neuromarketing: Analyzes consumer behavior and brain responses to marketing stimuli.
- Brain-Computer Interfaces: Develops systems that allow direct communication between the brain and external devices.
Technical Aspects
- Volume Conduction: The process of electrical signals passing through the brain’s tissues to reach the electrodes. This necessitates correction for accurate interpretation.
- Electrode Placement:
- International 10-20 System: Standardized method for placing electrodes on the scalp, ensuring consistent and comparable results.
Advantages and Limitations:
- Advantages:
- Non-invasive, relatively simple, and cost-effective.
- Portable and doesn’t require confinement in a small space.
- Does not emit radiation.
- Limitations:
- Bias towards detecting signals near the scalp.
- Difficulty in pinpointing the exact origin of deeper brain activity.
- Requires correction for volume conduction and noise.
Procedure
- Preparation: Patients should wash their hair without using conditioners or styling products. They may need to avoid caffeine and certain medications.
- During the Test:
- Electrodes are attached to the scalp, and the patient is asked to relax and remain still.
- The procedure typically lasts 20-40 minutes, but can be longer for specific conditions.
- After the Test: Electrodes are removed, and any sedatives administered during the test are allowed to wear off.
Affordability and Accessibility
- EEG is accessible and affordable compared to other neuroimaging techniques like MRI. It is widely used in clinical and research settings due to its simplicity and effectivenes.
Additional Points
- Risks: EEG is generally safe, though in rare cases it might trigger seizures in patients with epilepsy due to flashing lights or deep breathing during the test.
- Data Interpretation: The EEG data requires careful interpretation to account for noise and the effects of volume conduction, ensuring accurate diagnostic outcomes.
- Technological Integration: Modern EEGs often integrate with other imaging modalities such as MRI to improve spatial resolution and diagnostic accuracy.
Conclusion:
- Significance: EEG remains a crucial tool in both clinical diagnostics and scientific research, providing invaluable insights into brain function without invasive procedures. Its historical development and continued advancements underscore its importance in medical science.
Q) With reference to the applications of Electroencephalography (EEG), consider the following statements:
- EEG is the reference standard to diagnose epilepsy.
- EEG can confirm brain death, one of the two legally recognized forms of death in India.
- EEG can be used to detect abnormalities in brain structure similar to MRI.
Which of the statements given above is/are correct?
a) 1 and 2 only
b) 1 and 3 only
c) 2 and 3 only
d) 1, 2, and 3
Answer: (a)
Explanation
Statement 1 is correct.
- Definition and Role of EEG: Electroencephalography (EEG) is a non-invasive test that measures electrical activity in the brain. It involves placing electrodes on the scalp to detect and record brain wave patterns.
- Diagnosis of Epilepsy: EEG is considered the reference standard for diagnosing epilepsy because it can capture abnormal electrical activity in the brain, such as seizures. During a seizure, there are often distinct changes in brain wave patterns that can be detected by EEG. These patterns can help differentiate between different types of seizures and other conditions that might mimic epilepsy.
- Clinical Guidelines and Usage: The Indian Clinical Establishments Act and various medical guidelines underscore the importance of EEG in diagnosing epilepsy. It is the most reliable tool for detecting the electrical disturbances in the brain associated with epilepsy, making it essential in clinical practice for diagnosing and managing the condition.
Statement 2 is correct.
- Brain Death Definition: Brain death is defined as the irreversible cessation of all brain activity. It is one of the two legally recognized forms of death in India, the other being cardiac death.
- Role of EEG in Confirming Brain Death: EEG can be used to confirm brain death by showing a lack of electrical activity in the brain. This test is critical because it provides objective evidence of the absence of brain function, which is necessary for a brain death diagnosis.
- Clinical Protocols and Legal Framework: In India, the Transplantation of Human Organs and Tissues Act (THOTA) outlines the procedures for diagnosing brain death. EEG is listed as one of the confirmatory tests in these guidelines. The presence of a flat-line EEG (isoelectric line) is indicative of brain death.
Statement 3 is incorrect.
- Functional vs. Structural Imaging: EEG and MRI serve different purposes in medical diagnostics. EEG measures electrical activity and is primarily used to study brain function. In contrast, MRI (Magnetic Resonance Imaging) provides detailed images of brain structures.
- EEG’s Limitations in Structural Detection: While EEG is excellent for detecting functional abnormalities (e.g., seizure activity), it cannot provide detailed images of brain anatomy. It cannot identify structural abnormalities such as tumors, hemorrhages, or anatomical anomalies, which are detectable by MRI.
- Complementary Use: In clinical practice, EEG is often used in conjunction with MRI to provide a comprehensive view of a patient’s brain health. While EEG identifies functional abnormalities, MRI can reveal structural issues.