Synchronization between motor cortex and spinal motoneuronal pool during the performance of a maintained motor task in man.

Abstract

Simultaneous recordings of cortical activity, recorded as the magnetoencephalogram (MEG),and the electromyogram (EMG) of the ipsilateral and contralateral first dorsal interosseous muscles (1DI) were made during maintained voluntary contractions. 2. The MEG recorded from a localized region of the sensorimotor cortex of the dominant hemisphere was coherent with the EMG from the contralateral 1DI muscle over a limited band of frequencies. The peak coherence was confined largely within the beta range of cortical activity (13-35 Hz). Significant cortical activity at 10 Hz and 40-50 Hz was not correlated with motor output. The MEG and EMG from the ipsilateral 1DI muscle were uncorrelated at all frequencies. 3. Significant coherence between the MEG and the EMG was associated with synchronous behaviour between the MEG and EMG in the time domain. 4. The results demonstrate that synchronized cortical activity contributing to MEG activity within the beta range of frequencies during maintained voluntary contractions is coupled to motor output at frequencies of motor-unit activity associated with motor-unit synchronization. This observation provides further evidence for the involvement of cortical neurones in the generation of motor-unit synchronization. 5. We suggest that the coherence between MEG and contralateral EMG observed during maintained isometric contractions may provide an example of binding within the motor system.

Corticospinal Beta-Band Synchronization Entails Rhythmic Gain Modulation

“…1). During isometric contraction, the motor system engages in rhythmic synchronization in the beta-frequency range (Conway et al, 1995;Schoffelen et al, 2005Schoffelen et al, , 2008. This beta-band synchronization involves also the muscle, as can be seen from the rhythmicity of the example EMG in Figure 1 B.…”

Source Separation and Clustering of Phase-Locked Subspaces

“…Note that this real-valued matrix is the elementwise absolute value of the complex synchronization matrix Q defined in (2). The matrix R is symmetric and its elements can only take real values between 0 and 1.…”

“…Note that Q is exactly the synchronization matrix defined in (2). The Lagrangian for the maximization of E is thus L = c H Qc − λ(c H c − 1), and the solutions of the problem must obey ∇ c L = 0.…”

“…As an example, it has been shown that muscle activity measured with an electromyogram (EMG) and the activity of the motor cortex measured with an electroencephalogram (EEG) or magnetoencephalogram (MEG) have coherent oscillations when a person engages in a motor task. Because these coherent oscillations occur mostly in the beta-band 1 [2]- [5], the cortico-muscular coherence (CMC) phenomena are also denominated "beta-band synchronization," although some studies have shown that they also occur in other frequency ranges [6], [7]. It was also found that, again during a motor task, several brain regions oscillate coherently with one another [5], [8].…”

“…On the other hand, perturbations orthogonal to this cycle decay exponentially. 2 For these reasons, a weak interaction can have a long-lasting effect on an oscillator's phase, but the influence on its amplitude can be disregarded.…”