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Muscle artifacts, also known as myogenic potentials, are electrical activities recorded by an EEG that arise from muscle movements rather than the brain. They are characterised by surges in high-frequency activity and are commonly caused by the frontalis and temporalis muscles, such as when clenching the jaw or chewing. Muscle artifacts can also be caused by disorders such as hemifacial spasm and are typically identified by their duration, morphology, and rate of firing. While muscle artifacts are ubiquitous, there has been limited research and understanding of their complex nature, with most papers ignoring or leaving them untreated.
| Characteristics | Values |
|---|---|
| Definition | Muscle artifacts are defined as electrical activities arising from sites other than the brain. |
| Cause | Clenching of jaw muscles, chewing, tongue movement, and movement of the eyeball. |
| Identification | Muscle artifacts can be identified by their duration, morphology, and rate of firing. |
| Frequency | Muscle artifacts have very fast frequencies, usually in the range of 26.25-32.0 Hz, with an overall range of 15-32 Hz. |
| Location | Muscle artifacts are most commonly found in the frontal or lateral temporal regions and are minimal at the vertex. |
| State | Muscle artifacts are usually most prominent in the awake state. |
| Reduction methods | Human visual rejection, digital filters, and low-pass filters can be used to reduce muscle artifacts. |
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What You'll Learn
- Muscle artifacts are caused by myogenic activity, such as chewing or clenching jaw muscles
- They are characterised by surges in high-frequency activity
- They are most commonly found in the frontal or lateral temporal regions
- They can be reduced using digital filters or a low-pass filter
- They are more frequent during non-REM sleep
Muscle artifacts are caused by myogenic activity, such as chewing or clenching jaw muscles
Muscle artifacts, or myogenic artifacts, are electrical activities arising from sites other than the brain that are recorded during EEG (Electroencephalography). EEGs are designed to record cerebral activity, but they also pick up on electrical activity from muscle tissue on the skull. These muscle artifacts are characterised by surges in high-frequency activity and are easily identified due to their prominent frontal location. They are most commonly found in the frontal or lateral temporal regions due to the frontalis and temporalis muscles.
Chewing and clenching jaw muscles are examples of myogenic activity that can cause muscle artifacts. Chewing artifacts arise from the myogenic activity of the temporalis muscles during chewing and are marked by bursts of fast activity. Clenching jaw muscles, or the frontalis muscles, are also a common cause of myogenic artifacts. These muscle artifacts are identified by their shorter duration, morphology, and rate of firing compared to brain-generated potentials.
Other sources of myogenic artifacts include the tongue (hypoglossal) and eye movements. Tongue artifacts are caused by the mechanical movement of the tongue and are seen as diffuse slow activity. Eye movements, such as blinks and lateral eye movements, generate large-amplitude alternating current fields that are detected by electrodes near the eye.
Muscle artifacts can be reduced using various methods, such as digital filters or low-pass filters, but they are challenging to address due to the complex nature of muscle artifacts and the lack of accessible reduction methods.
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They are characterised by surges in high-frequency activity
Muscle artifacts, or myogenic artifacts, are electrical activities recorded by EEGs that arise from sources other than the brain. They are characterised by surges in high-frequency activity, often with low amplitude, overlying normal cerebral rhythms.
Myogenic potentials are the most common type of artifact. They are typically generated by the frontalis and temporalis muscles, for example, when clenching the jaw. The potentials produced by these muscles are of shorter duration than those generated in the brain and can be identified by their duration, morphology, and rate of firing.
In the context of EEG recordings during sleep, muscle artifacts are particularly noticeable as cortical EEG signals are intermingled with the electrical activity of the muscle tissue on the skull. A study found that muscle artifacts made up a substantial part (20-70%) of all-night EEG power density, with a frequency range of 15-32 Hz.
The detection of muscle artifacts is important for interpreting quantitative EEG data and distinguishing it from cortical activity. A simple algorithm can be used to detect bursts of myogenic activity by comparing high-frequency activity in each 4-second epoch with the activity level in a local 3-minute window.
Furthermore, muscle artifacts can be reduced or removed using various methods, such as digital filters or low-pass filters. However, the complexity of muscle artifacts and the lack of accessible reduction methods pose challenges in this area.
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They are most commonly found in the frontal or lateral temporal regions
Muscle artifacts, or myogenic potentials, are electrical activities arising from sites other than the brain that are recorded by EEG. They are most commonly found in the frontal or lateral temporal regions due to the frontalis and temporalis muscles. This includes the clenching of jaw muscles, as well as eye movements, which are observed on all EEGs. Lateral eye movements appear as a positive frontal deflection on the side the patient looks towards and a negative frontal deflection on the other side.
Myogenic artifacts are caused by muscle movements and are characterised by high-frequency, often low-amplitude activity overlying normal cerebral rhythms. They are usually most prominent in the awake state and are more predominant frontally, with only minimal myogenic activity near the vertex.
Chewing artifacts are a type of myogenic artifact that arises from the temporalis muscle during chewing. They are marked by sudden onset, intermittent bursts of fast activity, which may be accompanied by hypoglossal artifacts from the tongue.
Hemifacial spasm is a disorder that can produce repetitive muscle artifacts, and photomyoclonic response is a type of EMG artifact that occurs during intermittent photic stimulation.
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They can be reduced using digital filters or a low-pass filter
Muscle artifacts, or myogenic artifacts, are electrical activities recorded by EEG that arise from muscle movements, rather than the brain. They are commonly caused by the frontalis and temporalis muscles, such as when a patient is chewing or clenching their jaw.
These artifacts are characterised by very fast activity that often overlies normal cerebral rhythms. They are usually most prominent when the patient is awake and frontal or lateral temporal leads are most affected.
Digital filters are often applied to EEG recordings to remove unwanted signals and increase the SNR of target signals. They can be used to remove frequency components unlikely to be of cortical origin, such as muscle activity, skin potentials, or electrical line noise.
Low-pass filters, in particular, can be used to remove unwanted high-frequency components from muscle artifacts. This is achieved by smoothing the data, which helps to increase the SNR of target signals. The use of low-pass filters can be crucial in enabling a confident clinical read that is not skewed by unwanted signals.
However, it is important to note that filters can also introduce artifacts and affect the look and shape of the EEG tracings. Therefore, a well-trained EEG reader should be vigilant about possible filter artifacts and their impact on the clinical assessment of a patient's brain states.
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They are more frequent during non-REM sleep
Muscle artifacts, or myogenic potentials, are electrical activities arising from sites other than the brain that are recorded during EEGs. They are caused by muscle movements, particularly the frontalis and temporalis muscles, and are identified by their shorter duration, morphology, and rate of firing. They are characterised by surges in high-frequency activity and are usually most prominent in the awake state.
During sleep, muscle artifacts are more frequent towards the end of non-REM sleep episodes when EEG slow-wave activity declines. Within and across REM sleep episodes, muscle artifacts are evenly distributed. This is likely because, during non-REM sleep, the brain is less active, and the electrical activity of the muscle tissue on the skull is more noticeable.
EEG recordings use scalp electrodes, which means that cortical EEG signals are often intermingled with the electrical activity of the muscle tissue on the skull. This is especially true during non-REM sleep, when the brain is less active and the muscle activity is more noticeable in the recording.
The detection of muscle artifacts is important for interpreting quantitative EEG data and distinguishing between cortical and myogenic activity. A simple algorithm can be used to detect bursts of myogenic activity by comparing high-frequency activity in each 4-second epoch with the activity level in a local 3-minute window.
In summary, muscle artifacts are more frequent during non-REM sleep due to the brain's reduced activity, allowing the electrical activity of the muscles to be more prominent in the EEG recording. This knowledge helps in understanding and interpreting EEG data accurately.
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Frequently asked questions
Muscle artifacts, or myogenic potentials, are electrical activities recorded by an EEG that arise from muscles in the body rather than the brain.
Muscle artifacts are caused by the electrical activity of muscle tissue, especially the frontalis and temporalis muscles. They are often caused by the clenching of jaw muscles or chewing.
Muscle artifacts are characterised by surges in high-frequency activity and are usually more prominent frontally and laterally. They are also identified by their shorter duration compared to brain-generated potentials.
Muscle artifact reduction methods include human visual rejection of EEG segments with strong muscle artifacts and the use of digital filters to automatically identify and reject these segments.
