How EEG Works: Unlocking Mysteries Of The Mind
Electroencephalography (EEG) is a non-invasive way to measure electrical activity in the brain. By placing electrodes on the scalp, it records the signals produced when groups of neurons fire. Researchers, clinicians, and scientists use EEG to understand how the brain works during different activities, emotions, and states of health. From sleep disorders and epilepsy to attention and learning, EEG helps us explore what happens inside our heads.
How EEG Works
The Role of Neurons
Neurons are the brain’s basic building blocks. They send information to each other using small bursts of electrical and chemical signals. When many neurons fire together, they create patterns of electrical activity. These patterns pass through the skull and scalp. Although the signals weaken, sensitive electrodes can still pick them up.
Recording Electrical Activity
To record these signals, an EEG uses multiple electrodes placed at standard points on the scalp. We often rely on the “10-20 system” to ensure consistent placement. Each electrode picks up a tiny electrical voltage produced by the underlying brain tissue. Because these signals are very weak (measured in microvolts), we use amplifiers to boost them.
Transforming Signals into Waveforms
The EEG device converts the measured voltages into visual waveforms on a computer screen. These waveforms show how the brain’s electrical activity changes over time. Different types of brain waves—such as alpha, beta, delta, theta, and gamma—have their own characteristic patterns. Each pattern can reflect a certain state, like relaxation (alpha waves) or intense focus (beta waves).
What EEG Detects
Excitatory and Inhibitory Inputs
EEG does not measure single neurons firing. Instead, it picks up the combined effect of many neurons. These neurons send and receive signals at synapses, where chemical messengers (neurotransmitters) pass information. When one neuron excites another, it creates an excitatory post-synaptic potential (EPSP). This effect makes the next neuron more likely to fire.
In contrast, inhibitory post-synaptic potentials (IPSPs) make the next neuron less likely to fire. Both EPSPs and IPSPs contribute to the electrical currents that EEG detects. The balance of these signals shapes the overall rhythmic activity seen in the EEG. By analysing these rhythms, we gain insights into normal brain function and various disorders.
Brain Wave Patterns
The different frequency bands in the EEG—delta (up to 4 Hz), theta (4–8 Hz), alpha (8–13 Hz), beta (13–30 Hz), and gamma (above 30 Hz)—often link to specific brain states. For example, delta waves tend to dominate deep sleep, while alpha waves may appear during relaxed wakefulness. By studying these patterns, we can learn how the brain switches gears during different tasks or states.
How To Read EEG
Understanding Montages
A “montage” is a way of arranging EEG signals to compare different electrode sites. Using various montages helps us spot patterns or abnormalities. Consider montages as different “views” of the same data. Each view highlights certain features.
Bipolar Montage
In a bipolar montage, we compare the signal from one electrode to a nearby electrode. This approach emphasises differences in activity between two areas. It can help locate where unusual brain activity starts.
Referential Montage
A referential montage compares each electrode’s signal to a single reference electrode. This reference sits in a relatively “quiet” area of the scalp. The method offers a clearer look at how each brain region behaves compared to this baseline.
Average Reference Montage
In an average reference montage, we create a reference by averaging all the electrodes’ signals together. Then we compare each electrode to this average. This method can give a balanced overview of brain activity, reducing the impact of a single “noisy” site.
Laplacian Montage
A Laplacian montage compares each electrode’s signal to a weighted average of its neighbours. This sharpens the focus on local activity and reduces the influence of distant signals. It can make it easier to pinpoint where certain patterns come from.
Conclusion
EEG offers a practical, non-invasive way to study the brain’s electrical activity. It detects the combined signals from many neurons as they send excitatory and inhibitory messages. By recording these signals, EEG reveals patterns that correlate with different mental states, levels of alertness, or medical conditions. We can then analyse these signals using various montages, each providing a unique perspective.
The knowledge gained from EEG helps us understand conditions like epilepsy and sleep disorders. It also guides research into attention, learning, and emotion. As EEG technology advances, it becomes more portable and user-friendly, opening doors to new applications. By using EEG, we take another step towards unlocking the mysteries of the mind.
Thank you for reading and please comment on YouTube with any questions that you have! Click here to see the other blogs and associated videos I have about neuroscience! 🙂
If you want to support this educational neuroscience content, please consider becoming a Patreon 😊
References
Introduction to EEG – https://pubmed.ncbi.nlm.nih.gov/29673530/
Interpreting Findings – https://pubmed.ncbi.nlm.nih.gov/38116690/
EEG in epilepsy – https://pubmed.ncbi.nlm.nih.gov/19248841/