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Do you know the difference between electroencephalogram (EEGs) and event-Related Potentials (ERPs)?
EEGs (electroencephalograms) are a method of measuring brain activity using electrodes (from 25 to 34, and more for deeper insights into brain activity) placed on the scalp with a conductive gel. These electrodes are able to detect the tiny electrical activity that occurs when action potentials ‘fire’ in a neurone, also known as nerve impulses. This neuronal activity is detectable.
EEG performed on a person's head, Flaticon
These electrical charges are then graphed over time to give an indication of the level of activity occurring in that particular area of the brain, usually in response to a stimulus or test. These waves indicate some form of functional activity in a particular brain area, likely in response to the stimulus, event, or test the person is experiencing.This activity is then plotted as a result on a graph that provides the data in the form of 4 different types of waves known as:
Alpha.
Beta.
Theta.
Delta.
These waves differ in two points: amplitude and frequency.
The amplitude is the intensity and size of the waves.
The frequency is the speed and quantity of the waves.
Ten seconds of simulated EEG data, Wikimedia Commons
Sometimes the waves differ depending on whether a person is asleep or awake. The example above shows some recognisable patterns of waves. They are consistent and can be easily categorised.
However, these types of waves can be synchronised or desynchronized.
Synchronised waveforms usually occur when the person is asleep or focused on a task and can be categorised as alpha, beta, delta, and/or theta waves.
Desynchronized waveforms are more the norm when people are awake, as their brain rapidly switches attention and function. This usually results in a mixture of the above wave types, which is why amplitude and frequency vary so much.
Alpha waves are usually associated with sleep. However, they also occur when people are awake and relaxed. Beta waves occur when a person is awake and alert or at REM, and theta and delta waves occur when a person is in light and deep sleep, respectively.
EEGs are also good for detecting diseases such as epilepsy in a person because epilepsy interrupts the signals normally sent through neurons in the brain. This results in abnormal behaviours or responses such as muscle spasms and seizures.Identifying recognisable waveforms during sleep allows clinicians to determine if the person is suffering from a sleep disorder. EEGs are also used to detect brain activity in other diseases such as Alzheimer's disease.
Event-related potentials (ERPs) are very similar to EEG because they use electrodes placed on the scalp to measure electrical activity in the brain.ERPs differ, however, in the way they measure responses to a stimulus, namely by exposing the participant to the stimuli many times.
This process is called averaging, which produces a graph of average results showing recorded brain waves over time.
ERP averaging response times, GNU Free Documentation Licence, Wikimedia Commons
The graph above shows the neuron's activation potential and time after a stimulus.Latency is the time elapsing between showing the stimulus to the participant and their response to it. ERPs and EEGs usually have a short latency in the first 100ms, referred to as sensory ERPs because the senses respond reflexively to the stimulus.After 100ms comes the actual response to the stimulus, where the information has been processed cognitively.
Here we discuss the strengths and weaknesses of event-related potentials and electroencephalograms, as both are similar techniques with similar advantages and disadvantages.However, one of the major things we can suggest by using EEGs and ERPs is that these areas can be associated with specific responses and behaviours when measured.
¹Martha Ann Bell and Kimberly Cuevas, Using EEG to Study Cognitive Development: Issues and Practices, Journal of cognition and development: official journal of the Cognitive Development Society, 2012.
¹Martha Ann Bell, A psychobiological perspective on working memory performance at 8 months of age, Child Development, 2012.
They are both brain scanning techniques that use electrodes to measure brain electrical activity, providing data in the form of brain waves to suggest areas of activation.
EEGs and ERPs are both measuring techniques and are similar as they use electrodes to measure the brain's electrical activity. They do not measure each other.
An electroencephalogram EEG is a measuring tool for detecting electrical activity within the brain by attaching electrodes to the scalp.
An event-related potential (ERP) measures electrical activity within the brain, averaging out the results to eliminate ‘noise’ or random, unassociated brain activities.
Electrical (functional) activity in the brain.
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