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) and event-Related Potentials (ERPs).
- First, we will establish how electroencephalograms (EEGs) and event-Related Potentials (ERPs) work, defining EEGs and ERPs.
- We will discuss the components of electroencephalograms (EEGs) and event-related potential (ERPs) components.
- Then, we will highlight the differences between event-related potential (ERPs) vs EEGs, covering various Event-related potential examples.
- Finally, we will discuss the electroencephalograms (EEGs) and event-Related Potentials (ERPs) strengths and weaknesses.
Fig. 1: EEGs and ERPs measure brain activity.
Electroencephalograms (EEGs) and Event-related Potential (ERPS): Preparations and Procedures
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:
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):
- Delta (0.5 to 4Hz)
- Theta (4 to 7Hz)
- Alpha (8 to 12Hz)
- Sigma (12 to 16Hz)
- Beta (13 to 30Hz)
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.
Conditions Diagnosed with an EEG
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.
What can affect EEGs and ERPs?
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):
- Participants age
- Consciousness (are participants awake or asleep?)
- Biological and environmental stimuli
- Physical and mental activity
Event-related Potentials (ERPs) vs EEGs: What are ERPs?
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.
Event-Related Potential Components: ERP Brain Scam
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.
- Miltner et al. (2005) investigated phobias using ERPs. Phobias included fear of snakes and spiders, and they specifically investigated cortical responses and valence/arousal ratings in response to these phobias, comparing phobics to healthy controls.
- They found larger amplitudes of late ERP components, including the P3 we discussed above, but not of the earlier ERP components, such as the N2, when phobics were looking at fear-inducing stimuli.
Electroencephalogram (EEGs) vs Event-Related Potentials (ERPs) Strengths and Weaknesses
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.
Strengths
First, let's explore the strengths of using EEGs and ERPs.
- Low cost: Compared to other brain scanning techniques, EEGs and ERPs are a low-cost alternatives. They do not require extensive equipment and are more accessible than machines such as fMRIs (functional magnetic resonance imaging).
- Useful for clinical diagnosis: They are helpful in diagnosing diseases such as epilepsy, a condition that results from disturbed electrical activity in the brain.
- High temporal resolution: both techniques have a high temporal resolution because they record activity within milliseconds of its occurrence, unlike fMRI, which has a delay. It is highly accurate in timing the electrical activity in the brain.
- ERPs are robust: Because ERPs use an averaging method, their results are more reliable and can be attributed to activity because random activations are filtered out that have nothing to do with the brain activity occurring as a result of the stimulus.
- Non-invasive: Electrodes are placed on the scalp to detect activity. It is a non-invasive method of detecting brain activity.
- Mobility: The subject can move during the EEG or ERP examination, unlike fMRI, which requires the subject to stand still. This procedure allows for a wider range of tests to be performed on participants than is the case with other forms of brain scans.
- Tracking cognitive development: Both of Bells studies show how helpful EEGs were in testing children in different situations; in memory tasks at 8 months of age, and how robust these tests were.¹
Weaknesses
Now, let's explore the weaknesses.
- Low spatial resolution: Because the electrodes are on the scalp, they can only detect electrical activity deep in the brain. For example, it cannot tell what the amygdala is doing, only what the surface activity is doing. The spatial resolution is lower compared to other techniques, such as fMRI.
- Not accurate: EEG electrodes can provide a good estimate of where the electrical activity is occurring, but it is not accurate. It tells you where the electrical activity is the strongest, but not exactly where it comes from. EEGs typically represent the activity of the whole brain, rather than neurones specifically.
- Uncomfortable: The many electrodes combined with the gel make the device uncomfortable for participants. Also, the gel stays in the hair until it is washed off, so it can be very inconvenient for participants.
- EEGs lack the robustness of ERPs: EEGs capture activity that occurs throughout the brain, and do not use the averaging technique, making ERPs robust in comparison.
- As a result, more EEG samples are needed to provide accurate results, which is both time-consuming and inconvenient, and sometimes increases costs.
- Confounding Variables: Factors such as age, consciousness and environmental stimuli need to be accounted for. When they are not, confounding variables affect results.
Electroencephalogram (EEGs) and Event-Related Potentials (ERPs) - Key takeaways
- EEGs and ERPs measure electrical activity in the brain using electrodes attached to the scalp. ERPs differ from EEGs as the stimulus is presented multiple times to the participant, and the response is measured.
- Neurones activate and cause small electrical charges the electrodes detect, and they are then displayed graphically in the form of waves.
- These waves are alpha, beta, theta, and delta. Components of ERPs refer to one of the waves in otherwise complex waveforms, such as N1, N2, and P3.
- EEGs and ERPs have a high temporal resolution, are non-invasive, useful for clinical diagnosis (epilepsy), and are cheap compared to other techniques. ERPs are particularly robust due to their averaging technique.
- EEGs and ERPs have a low spatial resolution, are inconvenient, and provide superficial data (do not penetrate deeply into the brain to detect activity). Also, EEGs do not have the robustness of ERPs because they do not average the results.
References
- Fig. 2: Ten seconds of simulated EEG data by Laurens R. Krol, CC0, via Wikimedia Commons
- Nayak, C. S., & Anilkumar, A. C. (2020). EEG Normal Waveforms. StatPearls.
- Wang, W., Qi, M., & Gao, H. (2021). An ERP investigation of the working memory stroop effect. Neuropsychologia, 152, 107752.
- Fig. 3: Components of ERP by Choms and Mononomic licensed under the Creative Commons Attribution-Share Alike 3.0 Unported https://creativecommons.org/licenses/by-sa/3.0/deed.en via Wikimedia Commons
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