What is PLV value?

The PLV takes values on [0, 1] with 0 reflecting the case where there is no phase synchrony and 1 where the relative phase between the two signals is identical in all trials. PLV can therefore be viewed as a measure of trial to trial variability in the relative phases of two signals.

What is PLV EEG?

Phase Locking Value (PLV) is a statistic that can be used to investigate task-induced changes in long range synchronization of neural activity from EEG data. This method is introduced in Lachaux et al., (1999).

What is phase lag EEG?

Phase Lag Index is a tool to estimate connectivity in EEG in a way that eliminates volume conduction effects. However, it is also likely to discard a significant component of genuine interactions. In the previous blog posts I discussed coherence and phase locking value as measures of functional connectivity.

How to compute phase locking value?

Phase locking is an un-directed measure and is therefore symmetric [i.e., PLV(s1, s2) = PLV(s2, s1)]. Whole brain phase locking networks are computed between each pair of time series measurements on the cortical surface.

How does phase locking occur?

Phase locking refers to the tendency of a neuron to fire action potentials at particular phases of an ongoing periodic sound waveform, such as the sinusoidal waveforms that are typically used in physiological studies of the auditory system.

What is phase locking in the auditory system?

In the auditory system, phase locking refers to the fact that the probability of neuronal action potentials (spikes) varies as a function of the phase of low-frequency tones, low-frequency components of broadband sounds, or low-frequency fluctuations of the envelope (for review, see Joris et al., 2004; Heil and …

What is meant by phase lag?

Lagging phase refers to a wave that occurs “behind” another wave of the same frequency. When two signals differ in phase by -90 or +90 degrees, they are said to be in phase quadrature . When two waves differ in phase by 180 degrees (-180 is technically the same as +180), the waves are said to be in phase opposition .

How is functional connectivity measured?

1.2. Functional connectivity can be assessed with resting-state functional MRI (rs-fMRI), which measure the blood oxygenation level-dependent signal when subjects are positioned in the scanner in an awake-state without performing any particular task.

How do you do the Hilbert transform?

Hilbert transform of a signal x(t) is defined as the transform in which phase angle of all components of the signal is shifted by ±90o. x(t), ˆx(t) is called a Hilbert transform pair.

What is difference between PLL and FLL?

The FLL and PLL have similar structures that include discriminator, filter, and numerically controlled oscillator (NCO). However, their feedback parameters are different; namely, the FLL adjusts the frequency difference, and the PLL adjusts the phase difference. Hence, FLL and PLL have different performances.

What is meant by a Tonotopic map?

Tonotopic maps are a striking feature of the mammalian auditory cortex and underlie the representation of complex sounds, such as speech. This spatial separation of frequencies originates in the inner ear, where high frequencies are processed in the base of the cochlea and low frequencies in the apex.

What causes phase locking?

the tendency for a neural action potential to occur at a certain phase of a pure-tone stimulus. Typically, an action potential will not occur on every cycle, but when it is generated, it tends to occur at the same point or phase in the stimulus.

What causes phase lag?

It’s said that a capacitor causes a 90° lag of voltage behind current, while an inductor causes a 90° lag of current behind voltage. In phasor form, this is represented by the +j or -j in the inductive and capacitive reactance, respectively. But capacitance and inductance exist in all conductors to some extent.

What is fMRI functional connectivity?

Functional connectivity refers to the statistical relationship between specific physiological signals in time and are generally assessed using techniques such as functional magnetic resonance imaging (fMRI), electroencephalography (EEG) or magnetic electroencephalography (MEG).

What is FC fMRI?

Functional magnetic resonance imaging (fMRI)-based functional connectivity (FC) commonly characterizes the functional connections in the brain.

What are Hilbert transforms used for?

The Hilbert transform is a technique used to obtain the minimum-phase response from a spectral analysis. When performing a conventional FFT, any signal energy occurring after time t = 0 will produce a linear delay component in the phase of the FFT.

Is Hilbert transform real?

Analytic representation A Fourier transform property indicates that this complex heterodyne operation can shift all the negative frequency components of um(t) above 0 Hz. In that case, the imaginary part of the result is a Hilbert transform of the real part.

What is FLL in VLSI?

A frequency-lock, or frequency-locked loop (FLL), is an electronic control system that generates a signal that is locked to the frequency of an input or “reference” signal.