Miya Pearson
Electroencephalography (EEG) is a common tool used in sleep research to record brain activity. The placement of electrodes on the scalp is crucial for accurate EEG recordings. CZ (vertex) is a common reference point during wakefulness, but it is not recommended for sleep recordings. This is because certain brain wave patterns, such as sleep spindles, vertex waves, and K-complexes, appear falsely distributed across all EEG channels when using CZ as a reference during sleep. Sleep specialists may utilize alternative electrode placements, such as Fpz-Cz/Pz-Oz or C4-A1, to maintain the accuracy of sleep stage scoring without losing Rechtschaffen and Kales (R-K) balances.
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What You'll Learn
- CZ is an active reference, so it's not suitable for sleep recordings
- Sleep spindles, vertex waves, K-complexes, and saw-tooth waves appear falsely distributed across EEG channels
- The AASM Scoring Manual recommends a different EEG montage
- The FZ-CZ linkage may result in cancellation effects
- The earlobes are a more accurate reference point than the mastoid
CZ is an active reference, so it's not suitable for sleep recordings
The electroencephalogram (EEG) is the most common tool used in sleep research. It involves attaching electrodes to specific points on the head, which then record electrical activity in the brain. The placement of these electrodes is important, as it can affect the quality and accuracy of the recording.
CZ is an active reference electrode that can be placed on the centre line of the head. While it is a good choice of common reference during wakefulness, it is not suitable for sleep recordings. This is because certain brain activities, such as sleep spindles, vertex waves, K-complexes, and saw-tooth waves, are particularly prominent over the vertex (top of the head) and appear falsely distributed across all the EEG channels when using CZ as a reference. This means that the data recorded will not accurately reflect the brain activity during sleep, which is why CZ is not recommended as a reference electrode for sleep recordings.
The AASM Scoring Manual, which provides guidelines for EEG montage (the arrangement of electrodes), recommends a different montage for sleep recordings. It suggests linking right frontal, central, and occipital electrode placements to the left mastoid electrode (F4-M1, C4-M1, O2-M1). This montage ensures that the electrodes capture a comprehensive view of brain activity during sleep, including K-complexes, sleep spindles, and alpha waves, which are important for understanding sleep architecture and sleep quality.
It is worth noting that some researchers have explored alternative electrode placements, such as Fpz-Cz/Pz-Oz, which is an alternative to the international standard of C4-A1. These studies aim to determine if balances, such as the Rechtschaffen and Kales (R-K) balances, can be maintained while using different electrode placements. However, the standard recommendations and guidelines for electrode placement, such as those provided by the AASM Scoring Manual, are based on extensive research and are designed to optimize the accuracy and reliability of sleep recordings.
In summary, CZ is an active reference electrode that is not suitable for sleep recordings because it can lead to inaccurate distribution of brain activities across EEG channels. The AASM Scoring Manual and other standard protocols provide specific guidelines for electrode placement to ensure the accurate recording of sleep data.
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Sleep spindles, vertex waves, K-complexes, and saw-tooth waves appear falsely distributed across EEG channels
The electroencephalogram (EEG) is the most common tool used in sleep research. It is used to record and analyse sleep data. The placement of electrodes during EEG is important as it can affect the data recorded.
CZ is a good choice of common reference during wakefulness. However, it is not recommended during sleep as sleep spindles, vertex waves, K-complexes, and saw-tooth waves are particularly prominent over the vertex and appear falsely distributed across all the EEG channels. This is because CZ is an active reference.
The AASM Scoring Manual recommends an EEG montage that links right frontal, central, and occipital electrode placements to the left mastoid electrode (F4-M1, C4-M1, O2-M1). This montage helps to accurately record the dominant posterior rhythm, its posterior-anterior gradient, voltage asymmetries, and confirm and localize artifacts, malfunctioning electrodes, and asymmetries.
The placement of reference electrodes has been a topic of discussion, with some arguing for the use of mastoids over earlobes as reference points. The use of earlobes as reference points has been shown to significantly reduce EKG artifacts in the EEG. However, mastoids may be preferred due to the ease of attaching wires at this location.
Alternative electrode placements, such as Fpz-Cz/Pz-Oz versus C4-A1, have also been investigated in automatic sleep scoring. Studies have shown fair to good interobserver and interplacement agreement for both test and standard electrode placements.
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The AASM Scoring Manual recommends a different EEG montage
The American Academy of Sleep Medicine (AASM) published The AASM Manual for the Scoring of Sleep and Associated Events in 2007. This manual is a comprehensive and evolving resource that provides rules for scoring sleep stages, arousals, respiratory events during sleep, movements during sleep, and cardiac events. It also offers guidance on standard montages, electrode placements, and technical and digital specifications. The manual is considered the definitive reference for the scoring of polysomnography (PSG) and home sleep apnea tests (HSATs).
The recommended EEG montage by the AASM Scoring Manual is a common reference montage. It links right frontal, central, and occipital electrode placements to the left mastoid electrode (F4-M1, C4-M1, O2-M1). This montage is designed to be concordant with the International 10-10 System of electrode placement, which provides names and locations for additional electrodes by further dividing the distances between standard 10-20 placements.
The AASM Scoring Manual also allows for an alternative EEG montage, which is primarily a bipolar montage. For example, the 2-channel bipolar montage, FZ-CZ, CZ-OZ, can be used to confirm that sleep spindles are typically maximal over CZ. This montage can be useful when observing IEDs in an expanded EEG tracing, as it helps ensure that the reference does not involve the electrical field of the discharge.
The AASM Manual is regularly updated to incorporate new evidence and advancements in the field of sleep medicine. It is important for sleep specialists and technologists to be aware of these updates and take advantage of the flexibility offered by the manual in terms of EEG montages and derivations.
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The FZ-CZ linkage may result in cancellation effects
The electroencephalogram (EEG) is the most common tool used in sleep research. This tool is used to record and analyse sleep. The placement of electrodes is important, as distinct landmarks are identified on the head, and electrodes are placed at 10% or 20% intervals of the distance between the landmarks. The number of electrodes used depends on the purpose of the study.
The AASM Scoring Manual recommends an EEG montage that links right frontal, central, and occipital electrode placements to the left mastoid electrode. However, the FZ-CZ linkage is an alternative EEG montage that can be used to confirm that sleep spindles are typically maximal over CZ.
It is important to be aware of the potential for cancellation effects when using the FZ-CZ linkage, as it may impact the accuracy of the sleep recording and analysis.
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The earlobes are a more accurate reference point than the mastoid
The electroencephalogram (EEG) is the most common tool used in sleep research. It is used to record brain activity and is often used to study sleep patterns and disorders. The placement of electrodes on the scalp is crucial for accurate EEG readings.
The earlobes and the mastoid are both reference points for electrode placement in EEG recordings. The mastoid is the prominent bony projection behind the ear on the skull, while the earlobe is the soft, lower part of the ear.
While CZ (a point on the scalp between the top of the head and the forehead) is a suitable reference point during wakefulness, it is not recommended as a reference point for sleep recordings. This is because certain brain activities, such as sleep spindles, vertex waves, K-complexes, and saw-tooth waves, are prominent over the vertex and can appear falsely distributed across all EEG channels when using CZ as the reference.
The earlobes are considered a more accurate reference point than the mastoid for several reasons. Firstly, using the earlobes as reference points has been shown to significantly reduce EKG artifact in EEG recordings. This means that there is less interference or noise in the EEG signal, resulting in cleaner and more accurate data. Secondly, the earlobes are electrically 'silent' or less active compared to the mastoid. This is important because a reference point should ideally be electrically inactive to provide a neutral baseline for measuring brain activity.
Additionally, the classification of earlobes as either "free" or "attached" is a common misconception. In reality, earlobes exhibit continuous variation in attachment points, and their shape is likely influenced by multiple genes rather than a single gene with two alleles. This variation in earlobe morphology can impact the placement of electrodes and, consequently, the accuracy of EEG readings.
In conclusion, while CZ is suitable for wakefulness recordings, it is not the best choice for sleep studies due to its active nature. The earlobes are preferred over the mastoid as reference points because they reduce interference and provide a more electrically neutral baseline. Earlobe morphology can also impact electrode placement, highlighting the importance of accurate referencing in EEG recordings.
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Frequently asked questions
CZ is an active reference, and therefore a poor choice for common references during sleep because sleep spindles, vertex waves, K-complexes, and saw-tooth waves are particularly prominent over the vertex and appear falsely distributed across all the EEG channels.
CZ can be a good choice of a common reference during wakefulness.
The AASM Scoring Manual recommends an EEG montage, linking right frontal, central, and occipital electrode placements to the left mastoid electrode (F4-M1, C4-M1, O2-M1).
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