[뇌 및 인지과학 개론] Electroencephalogram (EEG)

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1. Electroencephalography (EEG)

Electroencephalography (EEG) records the electrical activity of the brain. It is performed in a dark and quiet brainwave examination room. Electrodes are attached to various parts of the scalp surface using a paste, then the electric activity is recorded by the amplifier. This technique gives a complete picture of human or animal brain activity without having to cut the skull. The EEG electrodes do not record the activity of any single neuron. It records the regular average activity of a group of cells under the electrode. The current produced by a single neuron is too small to be measured because it is obscured by various noise occurring inside and outside of the brain wave measuring device. However, when the brain is engaged in certain activities, a number of adjacent nerve cells are activated simultaneously. The relatively large current flow produced is conducted along the inside of the head and then produced a potential difference of greater than the noise level on the head surface and measured using a pair of electrodes. The electrical activity measured by EEG is not the sum of the activity potential caused by the firing of a single nerve cell, but rather the sum of post-synaptic positives occurring in the synapses. The EEG of normal person represents an activity with an amplitude of between 20 and 100 μV at a frequency domain of 1 to 30Hz. The observed frequencies are divided into groups such as alpha, beta, delta, theta. Researchers can determine if a person is asleep, dreaming, awake, or excited through EEG records. Abnormalities in EEG recordings may suggest that there is epilepsy, tumor, or other medical problems. Additionally, by using a method called evoked potential, researchers can record brain activity as a result of sensory stimulation and percutaneous stimulation of peripheral nerves.
2. History of EEG

In 1875, electrical activity was first measured from the exposed cerebral cortex of monkeys and rabbits by Richard Caton. In 1924, Hans Berger first recorded human scalp activities. He expanded previous studies and named a brainwave measuring device the electroencephalogram. In the 1950s, William Grey Walter developed an EEG topography, enabling the mapping of brain wave activity. The number of papers published using EEG is about 4,480 in 2000, 5,990 in 2005, 11,600 in 2010, 19,700 in 2015 and 21,100 in 2018, showing a trend that EEG is more used over time.
3. Advantages and Limitations of EEG

EEG provides very high time resolution, often recording between 250 and 2000Hz, and up to 20000Hz in modern systems. However, it provides very low spatial resolution, only being able to measure the active site within a few centimeters. EEG is easy to implement, cheaper, and the brainwave sensors are small and easy to move. It is also better known for measured signals than for other tests, and measurements are less affected by the tester's response and movements. It is useful for studies involving auditory stimuli because there is no noise, and it does not aggravate claustrophobia. However, EEG has a low spatial resolution in contrast with its time resolution, making it difficult to identify the specific location of various neurotransmitters and drugs. The brainwave connection also takes a long time because electrodes should be attached in a sophisticated location, and it has a poor signal to noise ratio.
4. Applications of EEG

EEG provides both researchers and clinicians with beneficial tools, especially in the fields of sleep physiology and epilepsy. EEG can be useful for discovering, treating and researching neurological disorders. In addition, brain-computer interface is based on research using EEG.

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1. Electroencephalography (EEG)

Electroencephalography (EEG) is a non-invasive neuroimaging technique that measures the electrical activity of the brain. It has been a valuable tool in the field of neuroscience, providing insights into brain function and dysfunction. EEG records the electrical signals generated by the synchronous activity of thousands of neurons in the cerebral cortex, allowing researchers and clinicians to study various brain states, such as wakefulness, sleep, and cognitive processes. The high temporal resolution of EEG, which can capture brain activity in the millisecond range, makes it particularly useful for studying the dynamics of neural processes. EEG has a wide range of applications, including the diagnosis of neurological disorders, the monitoring of brain activity during surgical procedures, and the development of brain-computer interfaces. While EEG has limitations, such as its relatively low spatial resolution and sensitivity to artifacts, it remains a crucial tool in the field of neuroscience and clinical neurology.
2. History of EEG

The history of electroencephalography (EEG) dates back to the late 19th century, when the German physician Hans Berger first recorded the electrical activity of the human brain in 1924. Berger's pioneering work laid the foundation for the development of EEG as a diagnostic and research tool. In the following decades, EEG technology advanced rapidly, with the introduction of improved amplifiers, electrodes, and recording techniques. The 1930s and 1940s saw the widespread adoption of EEG in clinical settings, particularly for the diagnosis of epilepsy and other neurological disorders. The 1950s and 1960s witnessed further advancements, including the development of quantitative EEG (qEEG) and the use of EEG in the study of sleep and cognitive processes. The advent of digital signal processing and computer technology in the 1970s and 1980s revolutionized EEG, enabling more sophisticated analysis and the integration of EEG with other neuroimaging modalities. Today, EEG remains an essential tool in both clinical and research settings, contributing to our understanding of the brain and its functions.
3. Advantages and Limitations of EEG

Electroencephalography (EEG) has several key advantages and limitations that make it a valuable yet complex tool in the field of neuroscience and clinical neurology. Advantages of EEG: 1. High temporal resolution: EEG can capture brain activity with millisecond-level precision, allowing for the study of rapid neural processes. 2. Non-invasive: EEG is a non-invasive technique, making it relatively safe and comfortable for participants, especially in clinical and research settings. 3. Portability: Modern EEG systems are portable, enabling the study of brain activity in natural environments and during everyday activities. 4. Cost-effectiveness: Compared to other neuroimaging techniques, such as functional magnetic resonance imaging (fMRI), EEG is generally more cost-effective, making it accessible to a wider range of researchers and clinicians. Limitations of EEG: 1. Low spatial resolution: EEG has relatively poor spatial resolution, as the electrical signals recorded at the scalp are the result of the summed activity of many neurons. This makes it challenging to pinpoint the precise location of neural activity. 2. Sensitivity to artifacts: EEG recordings can be contaminated by various artifacts, such as muscle movements, eye blinks, and electrical interference, which can complicate data analysis and interpretation. 3. Limited depth penetration: EEG is primarily sensitive to the activity of the cerebral cortex, as the electrical signals generated by deeper brain structures are attenuated and distorted by the intervening tissues. 4. Interpretation complexity: Interpreting EEG data requires specialized knowledge and expertise, as the patterns observed can be influenced by a variety of factors, including individual differences, task demands, and neurological conditions. Despite these limitations, EEG remains a valuable tool in the study of brain function and the diagnosis of neurological disorders, particularly when combined with other neuroimaging techniques and advanced data analysis methods.
4. Applications of EEG

Electroencephalography (EEG) has a wide range of applications in both clinical and research settings, making it a versatile and indispensable tool in the field of neuroscience. Clinical Applications: 1. Diagnosis of neurological disorders: EEG is widely used in the diagnosis and monitoring of various neurological conditions, such as epilepsy, brain tumors, head injuries, and neurodegenerative diseases. 2. Sleep studies: EEG is a crucial component of polysomnography, which is used to diagnose and study sleep disorders, such as sleep apnea, insomnia, and REM sleep behavior disorder. 3. Intraoperative monitoring: EEG is used during surgical procedures to monitor brain function and detect any potential complications or abnormalities. 4. Brain-computer interfaces: EEG-based brain-computer interfaces (BCIs) are being developed to assist individuals with physical disabilities, allowing them to control external devices or communicate through their brain activity. Research Applications: 1. Cognitive neuroscience: EEG is extensively used in cognitive neuroscience research to study the neural correlates of various cognitive processes, such as attention, memory, decision-making, and language. 2. Neuromarketing: EEG is employed in neuromarketing research to understand consumer behavior and preferences by measuring brain activity in response to marketing stimuli. 3. Neurofeedback: EEG-based neurofeedback techniques are used in research and clinical settings to train individuals to self-regulate their brain activity, with potential applications in the treatment of various neurological and psychiatric disorders. 4. Brain-computer interfaces: EEG-based BCIs are also used in research to develop new communication and control systems, as well as to study the neural mechanisms underlying brain-computer interactions. The versatility and non-invasive nature of EEG make it an invaluable tool in both clinical and research settings, contributing to our understanding of the brain and its functions, as well as the development of new diagnostic and therapeutic approaches.