Phase-Locking Value
Also known as: PLV, phase synchronization, phase coupling
Phase-Locking Value (PLV) is a frequency-domain measure of neural synchronization that quantifies the stability of phase difference between two signals. Introduced by Lachaux and colleagues in 1999, PLV detects phase coupling between brain regions independent of signal amplitude, enabling researchers to characterize functional connectivity from EEG and MEG recordings.
Key highlights
- Amplitude-independent; detects phase synchronization even when signal amplitudes are uncorrelated
- Computationally efficient; can be calculated from continuous time series without epoching
- High temporal resolution (millisecond scale) enables detection of transient synchronization
- Frequency-specific; naturally captures band-limited oscillatory interactions (alpha, beta, gamma)
- Mathematically well-founded in oscillatory network theory
Intuition
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How it works
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When to use it
PLV is appropriate for detecting phase-based functional connectivity in EEG/MEG, when interest is in communication patterns independent of amplitude (robust to amplitude fluctuations), and when frequency-specific interactions are hypothesized. Use PLV for band-limited oscillations (alpha, beta, gamma). Avoid PLV when amplitude covariance is the primary interest or when signal quality is poor (high artifact).
Strengths & limitations
- Amplitude-independent; detects phase synchronization even when signal amplitudes are uncorrelated
- Computationally efficient; can be calculated from continuous time series without epoching
- High temporal resolution (millisecond scale) enables detection of transient synchronization
- Frequency-specific; naturally captures band-limited oscillatory interactions (alpha, beta, gamma)
- Mathematically well-founded in oscillatory network theory
- Sensitive to volume conduction and electrical cross-talk between nearby electrodes; may inflate connectivity estimates
- Does not directly reflect information flow; high PLV indicates synchronization, not causality
- Assumes meaningful oscillations exist; applicable primarily to frequency bands with strong oscillatory activity
- Circular statistics require specialized statistical tests; standard parametric tests inappropriate
Common pitfalls
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Applications
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Frequently asked
How is PLV different from coherence?
Coherence measures both amplitude and phase coupling (correlation in frequency domain). PLV measures only phase coupling independent of amplitude. If two signals oscillate together but at different amplitudes, coherence is moderate while PLV is high. Use PLV when phase synchronization is the hypothesis, coherence when joint amplitude-phase coupling is the hypothesis.
Why is volume conduction a problem for PLV?
Volume conduction is electrical spread: a source near electrode A spreads to electrode B through the head tissue. Both electrodes receive highly correlated signals from that source, inflating PLV artificially. Volume conduction is strongest for nearby electrodes, so comparing long-distance electrode pairs reduces this artifact.
What statistical test should I use with PLV?
PLV is a circular statistic (angle-based), so standard parametric statistics (t-test) are inappropriate. Use permutation testing or bootstrap approaches to construct null distributions. Circular statistics packages (CircStat) provide specialized tests for comparing PLV across conditions.
Which frequency bands should I analyze?
Common bands are delta (1–4 Hz), theta (4–8 Hz), alpha (8–12 Hz), beta (12–30 Hz), and gamma (>30 Hz). Choose bands based on your hypothesis and the task. Resting-state connectivity is typically strongest in alpha and beta; event-related synchronization often appears in theta and gamma. Visualize power spectra to confirm oscillations exist.
Sources
- 1.Lachaux, J. P., Rodriguez, E., Martinerie, J., & Varela, F. J. (1999). Measuring phase synchrony in brain signals. Human Brain Mapping, 8(4), 194–208.
- 2.Varela, F., Lachaux, J. P., Rodriguez, E., & Martinerie, J. (2001). The brainweb: phase synchronization and large-scale integration. Nature Reviews Neuroscience, 2(4), 229–239.
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Cite this page
ScholarGate. (2026, June 3). Phase-Locking Value. ScholarGate. https://scholargate.app/neuroimaging/phase-locking-value