Connecting the brain's mu rhythm to multiple neural networks
The brain's sensorimotor mu rhythm is linked to several different neural networks, showing it is not just a simple indicator of movement control.
Source
Amplitude of Sensorimotor Mu Rhythm Is Correlated with BOLD from Multiple Brain Regions: A Simultaneous EEG-fMRI Study
Study at a glance
- Design
- Human experiment — Simultaneous resting-state EEG-fMRI correlating 8–12 Hz mu components with whole-brain BOLD
- N
- Healthy adults; N not stated as a single analytic total in the methods extract
- Population
- Healthy adults during resting-state simultaneous EEG-fMRI
- Outcome
- Correlation of sensorimotor mu-rhythm amplitude with BOLD across cortical and subcortical regions
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Connecting the brain's mu rhythm to multiple neural networks
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22 components
For each of the 22 components the mu power time series was estimated by the following steps.
8 Hz
Third, the EEG power spectrum for each epoch was calculated using a non-parametric multitaper approach with 3 tapers (), and the mu power of each epoch was estimated by averaging the power spectrum between 8 and 12 Hz.
What they did
Researchers recorded electrical brain activity and blood oxygen levels at the same time in healthy subjects resting in an fMRI scanner. They used a mathematical separation technique to isolate 22 specific mu rhythm components from the brain's electrical signals. They then mapped how fluctuations in these 8 to 12 Hz electrical waves over time matched up with blood flow changes across the entire brain.
What they found
The team discovered that higher mu rhythm power was associated with lower blood flow in networks responsible for movement planning, directing attention, and understanding others' perspectives. Conversely, higher mu rhythm power was linked to increased blood flow in the salience network, which notices important environmental events. These findings show that the mu rhythm is connected to a wide variety of brain networks rather than a single motor region.
The limits
What it doesn't show
Because this study looked at correlations during a resting state, it cannot prove that the mu rhythm directly causes changes in these brain networks, or vice versa. The researchers only looked at healthy participants, so these patterns might differ in clinical populations, such as individuals with autism. Additionally, the slow speed of fMRI imaging makes it impossible to determine the precise split-second timing of communication between the thalamus and the cortex during these oscillations.
Key terms
- mu rhythm
- A brain wave pattern of approximately 10 Hz detected over the motor cortex that is traditionally associated with physical movement.
- ICA (Independent Component Analysis)
- A statistical technique used to separate a mixed signal into its distinct, independent underlying sources.
- BOLD (Blood-Oxygen-Level-Dependent) signal
- An indirect measure of brain activity based on changes in blood oxygen levels detected by an fMRI scanner.
- mirror neuron system
- A network of brain cells that fires both when performing an action and when watching someone else perform that same action.
- salience network
- A collection of interconnected brain regions responsible for detecting and filtering important or unexpected environmental stimuli.
- theory of mind
- The cognitive ability to understand and attribute mental states, such as beliefs, desires, and intentions, to oneself and others.
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What was the main objective of this simultaneous EEG-fMRI study regarding the sensorimotor mu rhythm?
Common questions
Why is it important that the mu rhythm correlates with multiple brain systems?
Previously, scientists often assumed that changes in the mu rhythm only reflected motor system activity or mirror neuron activity. This study shows that mu rhythm fluctuations are tied to several systems at once, meaning researchers must be careful not to overinterpret what a change in this rhythm means during experiments.
What is the difference between the mu rhythm and the visual alpha rhythm?
Although both occur in the 10 Hz frequency range, the visual alpha rhythm is linked to visual processing areas and the default mode network, whereas the mu rhythm is tied to motor areas, the salience network, and social cognition networks.
How did the researchers make sure their results weren't just caused by participant movement?
They analyzed other brain wave frequencies, specifically the delta and beta bands. Since delta waves showed no correlation and beta waves showed distinct patterns, it confirmed that the mu rhythm correlations were reflecting genuine brain activity rather than general head movement.
What does a negative correlation between the mu rhythm and BOLD signal mean?
A negative correlation means that when the electrical mu rhythm gets stronger, the blood flow (activity) in those specific brain regions decreases, suggesting that the mu rhythm represents a resting or inhibited state of those networks.
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