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Do you know the difference between electroencephalograms (EEGs) and event-Related Potentials (ERPs)? EEGs are used in many different studies, providing valuable data on brain wave activity that professionals and researchers can assess and analyse. Sleep studies are core examples of areas of research using EEGs, for instance. So, how do EEGs and ERPs work? We are going to explore electroencephalograms (EEGs)…
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Jetzt kostenlos anmeldenDo you know the difference between electroencephalograms (EEGs) and event-Related Potentials (ERPs)? EEGs are used in many different studies, providing valuable data on brain wave activity that professionals and researchers can assess and analyse. Sleep studies are core examples of areas of research using EEGs, for instance. So, how do EEGs and ERPs work?
Fig. 1: EEGs and ERPs measure brain activity.
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.
According to Nayak and Anilkumar (2020):
EEG activity reflects the temporal summation of the synchronous activity of millions of cortical neurons that are spatially aligned.
The electrical charges detected by electrodes are then graphed over time to give an indication of the level of activity occurring in that particular area of the brain. These waves indicate some form of functional activity in the brain, and in the case of ERPs (event-related potentials), 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.
The frequency is often the most cited aspect of waveforms, and each waveform has a general range (Nayak & Anilkumar, 2020):
Fig. 2: Ten seconds of EEG data highlights how brain waves appear¹.
The waves also change 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, waves can be synchronised or desynchronised.
Synchronised waveforms usually occur when the person is asleep or focused on a task.
Desynchronised waveforms are more the norm when people are awake, as their brain rapidly switches attention and function.
So measuring wave activity using an EEG can be a difficult process.
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 good for detecting diseases such as epilepsy in a person because epilepsy interrupts the signals normally sent through neurones 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.
It's important to account for confounding variables when conducting research, and this is still the case for EEGs and ERPs.
Confounding variables that can affect an EEG and ERP include (Nayak & Anilkumar, 2020):
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.
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.
Components of ERPs refer to one of the waves in waveforms, identified through their differences in polarity, timing, scalp distribution, sensitivity, and other factors (Woodman, 2010). As seen in the image below, examples of components include P1, N1, N2, and P3.
Fig. 3: The components of ERPs².
Examples of event-related potentials (ERPs) can be seen in research investigating different areas of psychology, such as memory.
Wang et al. (2021) conducted an ERP investigation of the working memory Stroop effect. It's helpful to refer to the image above to understand when components occur.
In relating to their ERP findings, they found greater N2 (second negative peak in the averaged ERP waveform, on average 190ms in) and P3 (an event-related potential related to the process of decision-making, on average 300ms in) activity for the incongruent than the congruent condition, and increased N2 but decreased P3 components for the neutral than the congruent and incongruent conditions.
ERPs can be used in other areas of research, too, beyond memory.
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.
First, let's explore the strengths of using EEGs and ERPs.
Now, let's explore the weaknesses.
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 are a technique used to measure the brain's electrical activity, using electrodes placed on the scalp. ERPs are a form of EEG; ERPs differ in that they present a stimulus multiple times to the participants to measure changes in brain activity to a specific response.
An electroencephalogram EEG is a measuring tool for detecting electrical activity within the brain by attaching electrodes to the scalp. They can be used in research to investigate brain activity, or in a medical setting to help diagnose disorders, such as epilepsy.
An event-related potential (ERP) measures electrical activity within the brain where a stimulus is presented multiple times to a participant. The results are averaged out, which eliminates ‘noise’ or random, unassociated brain activities, and links the brain activity response to the stimulus.
ERPs measure electrical activity in the brain, which occurs when action potentials ‘fire’ in a neurone, also known as nerve impulses.
EEGs have a low spatial resolution, they are not entirely accurate, the conductive gel used is uncomfortable, confounding variables may affect results if not accounted for, and EEGs lack the robustness of ERPs.
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