ElectroEncephaloGram

Introduction

How it works

Electrical Activity of the Brain

Wave Frequency Bands

EEG Hardware, Equipment, and Setup

Typical EEG Setup Steps

Electrode Placement (10-20 system)

Summary Table

Standardized EEG Data Acquisition Protocol

Research in Happiness Science

Applications of EEG

Limitations

Videos

Introduction to EEG and BrainWave Analysis

EEG Demonstration with Emotiv EPOC X

EEG Experimentation with Stroop Test

References

Introduction

Electroencephalography (EEG) is a non-invasive technique for recording the brain’s electrical activity using electrodes placed on the scalp. Developed by Hans Berger in 1929, EEG captures the synchronized electrical impulses generated by millions of neurons, primarily in the cerebral cortex. These signals appear as wavy lines on a computer and reflect different brain states, such as wakefulness, relaxation, or sleep, with characteristic frequency bands: delta, theta, alpha, beta, and gamma.

Fig 1: Participant in EEG observation

EEG is widely used in both clinical and research settings. Clinically, it helps diagnose and monitor conditions like epilepsy, seizure disorders, sleep disorders, encephalitis, brain tumors, and brain dysfunction after injury or stroke. It is also used to assess coma and brain death, and to monitor brain activity during surgery. In research, EEG provides excellent temporal resolution, allowing scientists to study rapid brain processes and cognitive functions.

The EEG procedure is safe and painless. Electrodes, often arranged in standardized patterns, detect voltage differences caused by neural activity, which are then amplified and recorded. While EEG has limited spatial resolution compared to imaging techniques like MRI, it remains invaluable due to its ability to track real-time brain dynamics and detect abnormal patterns, such as those seen in epilepsy or sleep disorders.

How it works

Electrical Activity of the Brain

The brain’s electrical activity arises from billions of neurons communicating through rapid electrical and chemical signals. Here’s a concise explanation, accompanied by a diagrammatic representation:

How Electrical Activity Is Generated :

Neurons maintain a resting membrane potential by pumping ions (charged particles) in and out of the cell.
When a neuron is stimulated, it generates an action potential—a rapid change in electrical charge that travels along its axon.
At the synapse, this electrical signal can trigger the release of neurotransmitters (chemical messengers), which then excite or inhibit neighboring neurons, allowing the signal to propagate.
Large groups of neurons firing together, especially pyramidal neurons in the cortex, create synchronized electrical fields. These fields travel through brain tissue, skull, and scalp—a process called volume conduction—and can be detected by electrodes as EEG signals.

This collective neuronal activity forms the basis of the EEG, allowing us to see the brain’s electrical rhythms from outside the skull.

Fig. 1: Neural Communication and Signal Transmission

Wave Frequency Bands

EEG signals are categorized into distinct frequency bands, each associated with different brain states and functions. Here’s a concise overview:

Fig. 2: Frequency Wave Graph

EEG Hardware, Equipment, and Setup

Typical EEG Setup Steps

Prepare the scalp (clean and, if needed, part hair at electrode sites).
Apply conductive gel/paste to electrodes.
Place electrodes on the scalp according to the chosen system (e.g., 10-20).
Attach reference electrode (usually on earlobe or mastoid).
Connect electrodes to amplifier and data acquisition system.
Power on the amplifier and ensure all connections are secure.
Launch EEG software on the computer to monitor and record signals.
Check signal quality and adjust electrodes or gel as needed.
Begin recording and monitor data in real time.

Modern EEG systems can be stationary or portable, wired or wireless, and are scalable for different research or clinical needs. Proper setup ensures high-quality, artifact-free recordings essential for accurate brain activity analysis.

Fig. 3: Schematic Diagram of an EEG Machine

Electrode Placement (10-20 system)

The most widely used method for EEG electrode placement is the 10-20 system, which ensures standardized, reproducible, and anatomically meaningful positioning of electrodes across different individuals and studies.

Key Principles:

The "10" and "20" refer to the distances between adjacent electrodes, which are either 10% or 20% of the total front-back or right-left measurement of the skull.
Measurements are taken from anatomical landmarks: the nasion (bridge of the nose), inion (bump at the back of the skull), and preauricular points (just in front of the ears).
Electrodes are placed at intervals of 10% or 20% along these lines, ensuring proportional coverage of the entire scalp, regardless of head size or shape.

Electrode Naming:

Letters indicate the underlying brain region:
- Fp = Frontal pole
- F = Frontal
- C = Central
- T = Temporal
- P = Parietal
- O = Occipital
Numbers indicate hemisphere and distance from midline:
- Odd numbers = left hemisphere
- Even numbers = right hemisphere
- ‘z’ (zero) = midline

Example:

Fp1: Left frontal pole
Fz: Frontal midline
P4: Right parietal

Why Use the 10-20 System?

Ensures electrodes are placed over consistent brain regions for every subject.
Allows for reliable comparison across sessions and individuals.
Supports reproducibility in clinical and research applications.

Extensions:

Higher-density systems (10-10, 10-5) add more electrodes between standard positions for finer spatial resolution.

Summary Table

The 10-20 system is the foundation for consistent and accurate EEG recordings worldwide.

Fig. 4: The 10-20 System of Electrode Placement

Standardized EEG Data Acquisition Protocol

Preparation
- Greet the participant and explain the procedure to ensure they feel comfortable and informed.
- Ask the participant to remove any jewelry or accessories that might interfere with the electrodes.
- Measure the participant’s head using a flexible tape, marking key anatomical landmarks (nasion, inion, preauricular points) with a washable marker.
- Based on these measurements, mark electrode positions on the scalp according to the 10-20 system.
Electrode Placement
- Gently clean each marked spot on the scalp with an alcohol wipe or abrasive gel to reduce impedance and ensure good signal quality.
- Apply a small amount of conductive gel or paste to each electrode.
- Attach the electrodes to the scalp, either individually or using a pre-fitted electrode cap, making sure each is secure and comfortable for the participant.
- Attach a reference and ground electrode, usually on the earlobe or mastoid.
System Connection
- Connect the electrode wires to the EEG amplifier and data acquisition system.
- Check all connections and power up the equipment.
- On the computer, open the EEG recording software and verify that all channels are active and displaying signals.
Signal Quality Check
- Monitor the impedance levels for each electrode, ensuring they are within the acceptable range (usually below 10 kΩ).
- If any channels show high impedance or noise, reapply gel or adjust the electrode until the signal is clean.
- Ask the participant to relax and minimize movement to reduce muscle and movement artifacts.
Recording
- Instruct the participant on the tasks they may need to perform (e.g., open/close eyes, respond to stimuli, remain still).
- Begin the recording session, observing the EEG traces in real time for any artifacts or abnormalities.
- Throughout the session, note any events or participant movements that could affect the data.
Data Management
- Once recording is complete, carefully remove the electrodes and clean the participant’s scalp.
- Save and back up the EEG data, labeling the files with participant and session information.
- Document any observations or issues encountered during the session for the research team.

Research in Happiness Science

Study on Emotional Context, Temperament, and ERP Markers in Children

This study examined how emotional context (anticipation of public speaking) and temperament (shyness) influence attention and error monitoring in children (~7 years old). Participants completed a visual cueing task under neutral and emotionally salient conditions while EEG was recorded. ERP analysis focused on the N1 (early attention) and N2 (cognitive control) components. Results showed that shy children exhibited enhanced N2 amplitudes in the emotionally salient condition, suggesting greater sensitivity to emotional stress during cognitive tasks. ( Henderson, 2010 )

EEG Study on Emotional Face Processing in Children

This study examined how children process emotional facial expressions using EEG, focusing on early ERP components like N170 (linked to face perception) and LPP (late positive potential, associated with emotional salience). Children (ages 6–12) passively viewed images of happy, angry, and neutral faces while their brain activity was recorded via EEG. Results showed that emotional faces elicited greater LPP amplitudes, especially for angry faces, indicating increased attentional and emotional processing. The N170 component was larger for faces compared to non-face stimuli, confirming early face sensitivity. ( Batty, 2006 )

Fig: 5 Examples of stimuli used in this implicit emotional task. Women’s and men’s faces expressing anger, disgust, happiness, fear, surprise and sadness, as well as faces with neutral expression, were used.

Applications of EEG

Clinical Applications

Epilepsy and Seizure Disorders:
EEG is the gold standard for diagnosing epilepsy and differentiating between seizure types. It helps localize seizure foci and guides treatment decisions.
Sleep Disorders:
Used to diagnose conditions such as sleep apnea, narcolepsy, and insomnia by monitoring brain activity during different sleep stages.
Brain Tumors and Injuries:
EEG detects abnormal patterns linked to tumors, traumatic brain injury, or brain infections, aiding in diagnosis and monitoring.
Neurological Diseases:
Supports the diagnosis and management of conditions like Alzheimer’s, Parkinson’s, and rare genetic diseases. EEG can track disease progression and serve as a biomarker in clinical trials.
Stroke Analysis:
Assists in identifying regions affected by stroke and monitoring recovery.
Perioperative and Intensive Care Monitoring:
EEG is used during surgery and in intensive care units to monitor depth of anesthesia, detect cerebral insults (e.g., ischemia), and prevent postoperative delirium and cognitive decline.
Psychiatric and Cognitive Evaluation:
Assesses cognitive states, classifies psychiatric symptoms, and evaluates the effects of medical and psychological treatments, including cognitive-behavioral therapy.

Research and Experimental Applications

Neuroscience and Cognitive Research:
EEG is central to studies on perception, attention, learning, memory, and consciousness. It helps map how the brain responds to specific stimuli and tasks.
Emotion and Affective Science:
Researchers use EEG to investigate how the brain processes different emotional states and to develop emotion recognition systems.
Brain-Computer Interfaces (BCI):
Enables communication and control of external devices for individuals with severe motor impairments, such as locked-in syndrome or cerebral palsy.
Human Factors and Neuromarketing:
EEG tracks mental workload, decision-making, and consumer behavior, and is used in usability studies and marketing research.
Experimental Psychology:
EEG is used to study how the brain changes in response to specific visual, auditory, or cognitive stimuli, providing insights into mental processes.