ELECTROENCEPHALOGRAPHY(EEG)
1. Context
This year marks the centenary of the first human EEG, produced by German physiologist Hans Berger. EEG measures electrical activity in the brain generated by neurons. In research, scientists use EEG for neuroscience, cognitive psychology, neurolinguistics etc
2. What is EEG?
- EEG stands for electroencephalography. The term combines "electro" for electricity, "encephalo" for brain, and "graphy" meaning to represent or show.
- Neurons in the brain function by moving electrically charged particles, such as ions, which create electrical activity.
- This activity can be visualized using an EEG test. Researchers have been able to correlate EEG data with various levels and types of brain activity, distinguishing between normal and abnormal states.
- EEG is a common diagnostic tool in clinical settings. It is the gold standard for diagnosing epilepsy and can also reveal the effects of anesthesia, sleeping patterns, neurological activity during a coma, and oxygen availability. EEG can also confirm brain death, which is one of the two legally recognized forms of death in India.
- In research, EEG is used in fields such as neuroscience, cognitive psychology, neurolinguistics, neuromarketing, and in the development of brain-computer interfaces
3.Invention of EEG
The invention of the EEG (electroencephalography) is credited to Hans Berger, a German psychiatrist, who made significant contributions to the field in the early 20th century.
Here’s a brief overview of its development:
- Hans Berger is known for recording the first human EEG in 1924. He discovered that the brain's electrical activity could be recorded from the scalp using electrodes. Berger's initial experiments involved his son and himself, where he used a device called a galvanometer to measure the brain's electrical currents. His findings led to the identification of what is now known as the alpha wave, or Berger wave, a pattern of electrical activity in the brain.
- Berger's work was initially met with skepticism. However, his subsequent publications in the late 1920s and early 1930s provided more detailed accounts of his findings, which gradually gained acceptance in the scientific community. His work demonstrated that brain activity could be measured and correlated with various mental states and conditions.
- The development of more sophisticated equipment in the 1930s and 1940s, such as the cathode-ray oscilloscope, allowed for better visualization and recording of brain waves. This period saw a surge in research and clinical applications of EEG
- By the 1950s, EEG had become a standard tool in neurology and psychiatry. It was used to diagnose and monitor epilepsy, sleep disorders, and other neurological conditions. The ability to non-invasively measure brain activity revolutionized the understanding of brain function and disorders
- Over the decades, EEG technology has continued to evolve with advancements in digital recording, signal processing, and the development of portable and wearable EEG devices. Today, EEG is widely used in clinical practice, research, and even consumer applications, such as brain-computer interfaces and neurofeedback
4. What is Volume Conduction?
- Volume conduction refers to the process by which electrical signals, generated by active tissues such as neurons, travel through the surrounding conductive medium, typically biological tissues like the brain, scalp, and skull.
- This phenomenon is crucial in understanding how EEG (electroencephalography) works, as it affects the way electrical potentials recorded at the scalp reflect the underlying neural activity
- EEG records the brain's electrical activity produced by neurons. During the test, a healthcare professional places electrodes on the scalp. Between the electrodes and the neurons are multiple layers of skin, fluid, and bone.
- When neurons generate electrical activity, charged particles traverse these layers before reaching the electrodes, undergoing various transformations like reflection, refraction, and scattering along the way.
- Volume conduction describes the process by which electrical signals travel through this three-dimensional space.
- It also highlights that the electrical activity originates in one location while the detectors are positioned at a distance.
- The raw data captured by the electrodes must be adjusted to account for volume conduction effects and for noise from faulty electrodes or incidental physiological activities (like blinking or muscle movements). A clinician then interprets the cleaned and processed data
5. How does an EEG Work?
An electroencephalogram (EEG) is a method used to record electrical activity in the brain. Here's a concise explanation of how it works:
- Electrode placement: Small metal discs called electrodes are attached to specific locations on the scalp.
- Signal detection: These electrodes detect tiny electrical impulses produced by brain cells (neurons) when they communicate.
- Amplification: The signals are extremely weak, so they are amplified thousands of times.
- Recording: The amplified signals are then recorded as wavy lines on a computer screen or on paper.
- Analysis: Patterns in these waves can indicate normal or abnormal brain activity, helping diagnicians identify various conditions
6.Challenges with EEG
- The voltage changes detected by the electrodes are sent to a computer, which then plots these readings on a graph with voltage on one axis and time on the other. Health professionals typically focus on two key aspects of the graph: the voltage (measured in microvolts) and the frequency of the variations (measured in hertz).
- They also consider the location of the neurons generating the recorded electrical activity, such as in the neocortex or allocortex, the two main areas of the cerebral cortex.
- EEG excels at tracking rapid brain electrical activity, with a temporal resolution on the order of milliseconds.
- However, it is more sensitive to electrical signals from the surface of the cortex and particularly to currents generated by neurons’ dendrites, rather than those from axons. Determining the exact origin of electrical activity within the brain from EEG data is also complex.
- To address these challenges, researchers often combine EEG with other tests, like magnetic resonance imaging (MRI), and use advanced techniques for data acquisition, processing, and reconstruction
7.Way Forward
In addition to its measurement and diagnostic capabilities, an EEG setup is straightforward and cost-efficient.
The equipment is compact, does not emit high-energy radiation or loud noises, does not confine patients in small spaces like MRI machines, is non-invasive, and is portable (the invasive form of EEG is called electrocorticography, or ECoG).
However, despite these advantages, setting up an EEG test requires time. This includes applying a gel to the person's scalp and positioning the electrodes accurately according to the 10-20 System. Additionally, the readings can be influenced by factors such as the thickness of the person's hair
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For Prelims: Applications of EEG, Volume Conduction, EEG (Electroencephalography)
For Mains: GS III- Science& Technology -Detailed Mechanism of EEG
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Source: The Hindu
